Passing data between view controllers

Question

I m new to iOS and Objective-C and the whole MVC paradigm and I m stuck with the following  I have a view that acts as a data entry form and I want to give the user the option to select multiple products  The products are listed on another view with a UITableViewController and I have enabled multiple selections  How do I transfer the data from one view to another  I will be holding the selections on the UITableView in an array  but how do I then pass that back to the previous data entry form view so it can be saved along with the other data to Core Data on submission of the form  I have surfed around and seen some people declare an array in the app delegate  I read something about singletons  but I don t understand what these are and I read something about creating a data model  What would be the correct way of performing this and how would I go about it

User · Answer

I was searching this solution for long time, and at last I found it. First of all, declare all the objects in your SecondViewController.h file like

@interface SecondViewController: UIviewController
{
    NSMutableArray *myAray;
    CustomObject *object;
}

Now in your implementation file, allocate the memory for those objects like this:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
     self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
     if (self)
     {
         // Custom initialization
         myAray=[[NSMutableArray alloc] init];
         object=[[CustomObject alloc] init];
     }
     return self;
}

Now you have allocated the memory for Array and object. Now you can fill that memory before pushing this ViewController.

Go to your SecondViewController.h and write two methods:

-(void)setMyArray:(NSArray *)_myArray;
-(void)setMyObject:(CustomObject *)_myObject;

In the implementation file, you can implement the function:

-(void)setMyArray:(NSArray *)_myArray
{
     [myArra addObjectsFromArray:_myArray];
}

-(void)setMyObject:(CustomObject *)_myObject
{
     [object setCustomObject:_myObject];
}

Expecting that your CustomObject must have a setter function with it.

Now your basic work is done. Go to the place where you want to push the SecondViewController and do the following stuff:

SecondViewController *secondView= [[SecondViewController alloc] initWithNibName:@"SecondViewController " bundle:[NSBundle MainBundle]] ;
[secondView setMyArray:ArrayToPass];
[secondView setMyObject:objectToPass];
[self.navigationController pushViewController:secondView animated:YES ];

Take care for spelling mistakes.

User · Answer

Passing data between FirstViewController to SecondViewController as below For example  FirstViewController String value as StrFirstValue     quot first quot    So we can pass this value in the second class using the below steps   We need to create a string object in the SecondViewController h file  NSString  strValue    Need to declare a property as the below declaration in the  h file   property  strong  nonatomic   NSString  strSecondValue    Need synthesize that value in the FirstViewController m file below the header declaration   synthesize strValue   And in file FirstViewController h    property  strong  nonatomic   NSString  strValue    In FirstViewController  from which method we navigate to the second view  please write the below code in that method   SecondViewController  secondView    SecondViewController alloc   initWithNibName   quot SecondViewController  quot  bundle  NSBundle MainBundle       secondView setStrSecondValue StrFirstValue      self navigationController pushViewController secondView animated YES

User · Answer

This is not the way to do it  You should use delegates  I ll assume we have two view controllers  ViewController1 and ViewController2  and this check thing is in the first one and when its state changes  you want to do something in ViewController2  To achieve that in the proper way  you should do the below  Add a new file to your project  Objective-C Protocol  menu File   New  Now name it ViewController1Delegate or whatever you want and write these between the  interface and  end directives   optional  -  void checkStateDidChange  BOOL checked   Now go to ViewController2 h and add   import  quot ViewController1Delegate h quot   Then change its definition to   interface ViewController2  UIViewController lt ViewController1Delegate gt   Now go to ViewController2 m and inside the implementation add  -  void checkStateDidChange  BOOL checked        if  checked                  Do whatever you want here            NSLog   quot Checked quot                else                 Also do whatever you want here            NSLog   quot Not checked quot              Now go to ViewController1 h and add the following property   property  weak  nonatomic  id lt ViewController1Delegate gt  delegate   Now if you are creating ViewController1 inside ViewController2 after some event  then you should do it this way using NIB files  ViewController1  controller     NSBundle mainBundle  loadNibNamed   quot ViewController1 quot  owner self options nil  0   controller delegate   self   self presentViewController controller animated YES completion nil    Now you are all set  Whenever you detect the event of check changed in ViewController1  all you have to do is the below   delegate checkStateDidChange checked      You pass here YES or NO based on the check state of your control

User · Answer

Create the property in the next view controller  h file and define getters and setters  Add this property in NextVC h on nextVC   property  strong  nonatomic  NSString  indexNumber   Add  synthesize  indexNumber            in NextVC m And last NextVC  vc     NextVC alloc init    vc indexNumber     quot 123 quot     self navigationController vc animated YES

User · Answer

After more research it seemed that protocols and delegates were the correct Apple preferred way of doing this  I ended up using this example  in the iPhone development SDK   Sharing data between view controllers and other objects It worked fine and allowed me to pass a string and an array forward and back between my views

User · Answer

This is a very old answer and this is anti pattern  Please use delegates  Do not use this approach   1  Create the instance of the first view controller in the second view controller and make its property  property  nonatomic assign   2  Assign the SecondviewController instance of this view controller  2  When you finish the selection operation  copy the array to the first View Controller  When you unload the second view  the first view will hold the array data

User · Answer

I prefer to make it without delegates and segues  It can be done with custom init or by setting optional values   1  Custom init  class ViewControllerA  UIViewController     func openViewControllerB         let viewController   ViewControllerB string   Blabla   completionClosure    success in       print success             navigationController  pushViewController animated  true         class ViewControllerB  UIViewController     private let completionClosure    Bool  - gt  Void    init string  String  completionClosure    Bool  - gt  Void         self completionClosure   completionClosure     super init nibName  nil  bundle  nil      title   string        func finishWork         completionClosure           2  Optional vars  class ViewControllerA  UIViewController     func openViewControllerB         let viewController   ViewControllerB       viewController string    Blabla      viewController completionClosure     success in       print success            navigationController  pushViewController animated  true         class ViewControllerB  UIViewController     var string  String        didSet         title   string             var completionClosure    Bool  - gt  Void      func finishWork         completionClosure

User · Answer

Well  we have a few ways we can work with the delegates system or using storyboardSegue   As working with setter and getter methods  like in viewController h   property  retain  nonatomic  NSString  str   Now  in viewController m  synthesize str   Here I have a PDF URL and a segue to another viewController like this and pdfObject is my pdfModel  It is basically an NSOBJECT class   str    NSString stringWithFormat   quot    quot   pdfObject objPath    NSLog   quot pdfUrl                quot   pdfUrl      self performSegueWithIdentifier   quot programPDFViewController segue quot  sender self      pragma mark - Navigation      In a storyboard-based application  you will often want to do a little preparation before navigation   -  void prepareForSegue  UIStoryboardSegue   segue sender  id sender          if    segue identifier  isEqualToString   quot programPDFViewController segue quot                programPDFViewController  pdfVC    segue destinationViewController              pdfVC setRecievedPdfUrl str               Now successfully I received my PDF URL string and other ViewController and use that string in webview     As working with delegates like this I have one NSObject class of utilities containing my methods of dateFormatter  sharedInstance  EscapeWhiteSpaceCharacters  convertImageToGrayScale and more method I worked with throughout the application so now in file utilities h  In this  you don   t need to create variables every time parsing data from one to another view controller  One time  you create a string variable in file utilities h  Just make it nil and use it again    interface Utilities   NSObject  File Utilities h     Utilities  sharedInstance     property nonatomic  retain NSString  strUrl   Now in file utilities m    implementation utilities     utilities  sharedInstance         static utilities  sharedObj   nil       if  sharedObj    nil             sharedObj     utilities alloc  init               return sharedObj      Now it s done  come to your file firstViewController m and call the delegate NSString str    NSString stringWithFormat   quot    quot   pdfObject objPath    Connection sharedInstance  strUrl   nil   Connection sharedInstance  strUrl   str  Now go to you file secondViewController m directly  and use it without creating a variable In viewwillapear what I did   - void viewWillAppear  BOOL animated         super viewWillAppear YES          self webViewMethod  Connection sharedInstance  strUrl         - void WebViewMethod  NSString Url            Working with webview  Enjoy coding  D       This delegate work is reliable with memory management

User · Answer

I like the idea of model objects and mock objects based on NSProxy to commit or discard data if what the user selects can be cancelled  It s easy to pass data around since it s a single object or couple of objects and if you have  let s say  a UINavigationController controller  you can keep the reference to the model inside and all pushed view controllers can access it directly from the navigation controller

User · Answer

There are tons of ways to do this and it s important to pick the right one  Probably one of the biggest architectural decisions lies on how the model code will be shared or accessed throughout the app  I wrote a blog post about this a while back  Sharing Model Code  Here s a brief summary  Shared data One approach is to share pointers to the model objects between view controllers   Brute force iteration on view controllers  in Navigation or Tab Bar Controller  to set the data Set data in prepareForSegue  if storyboards  or init  if programmatic   Since prepare for segue is the most common here is an example  override func prepareForSegue segue  UIStoryboardSegue  sender  AnyObject         var next   segue destinationViewController as NextViewController     next dataSource   dataSource    Independent access Another approach is to handle a screen full of data at a time and instead of coupling the view controllers to each other couple each view controller to single data source that they can get to independently  The most common way I ve seen this done is a singleton instance  So if your singleton object was DataAccess you could do the following in the viewDidLoad method of UIViewController  func viewDidLoad         super viewDidLoad       var data   dataAccess requestData      There are addition tools that also help pass along data   Key-Value Observing NSNotification Core Data NSFetchedResultsController Data Source  Core Data The nice thing about Core Data is that it has inverse relationships  So if you want to just give a NotesViewController the notes object you can because it ll have an inverse relationship to something else like the notebook  If you need data on the notebook in the NotesViewController you can walk back up the object graph by doing the following  let notebookName   note notebook name  Read more about this in my blog post  Sharing Model Code

User · Answer

Use notification center to pass data from one view to another  The observer listener pattern works the best  The other workaround can be create the same objects in both classes  Create a class 2 object in class one  Access the data objects to be passed  set them  and then push the view controller

User · Answer

Pure Combine solution for UIKit and AppKit Let s take a simple example of passing an Int value of count between ViewControllers  A parent ViewController  VC  has a variable named count  and child ViewController can let the user change the value of count  Once the user is done changing the value  they will dismiss the child controller and parent VC should have the updated value after that   Parent View Controller ParentVC gets the updated value of count from the ChildVC class ParentVC  UIViewController       var count   1     var countObserver  AnyCancellable     1      override func prepare for segue  UIStoryboardSegue  sender  Any             let childVC   segue destination as  ChildVC         childVC sliderValue   count    2         countObserver   childVC  sliderValue    3              assign to    count  on  self            countObserver will retain the observer that would observe changes made by ChildVC  When the child appears  we assign the current count value from parent to a control  here UISlider  in the ChildVC  which becomes a starting point for modifying the value of count   We observe sliderValue  which is a publisher  that would emit the value of count that the user would change by dragging the slider  Note that we used  sliderValue instead of just sliderValue     Child View Controller ChildVC is the one that would emit values that ParentVC is interested in  class ChildVC  UIViewController        Published var sliderValue  Int   0    1       IBOutlet var sliderOutlet  UISlider        IBAction func slided   sender  UISlider            sliderValue   Int sender value             Published is Publisher that stores value and emits a signal when the value changes  It behaves just like a regular var but can publish values that can be accessed by prepending   sign to it    CurrentValueSubject and PassthroughSubject vs  Published  CurrentValueSubject can also be used instead of  Published  The only difference is  you would have to manually emit the signal  It is useful in cases where you want to control when to emit  For example  you can emit the value  but only if it falls in a specific range   PassthroughSubject also can be used instead of  Published or CurrentValueSubject  Here  the difference is PassthroughSubject cannot hold a value  it can just emit a signal  This can be useful when the value cannot be concretely represented in a variable

User · Answer

The OP didn t mention view controllers but so many of the answers do  that I wanted to chime in with what some of the new features of the LLVM allow to make this easier when wanting to pass data from one view controller to another and then getting some results back   Storyboard segues  ARC and LLVM blocks make this easier than ever for me   Some answers above mentioned storyboards and segues already but still relied on delegation   Defining delegates certainly works but some people may find it easier to pass pointers or code blocks   With UINavigators and segues  there are easy ways of passing information to the subservient controller and getting the information back   ARC makes passing pointers to things derived from NSObjects simple so if you want the subservient controller to add change modify some data for you  pass it a pointer to a mutable instance   Blocks make passing actions easy so if you want the subservient controller to invoke an action on your higher level controller  pass it a block   You define the block to accept any number of arguments that makes sense to you   You can also design the API to use multiple blocks if that suits things better   Here are two trivial examples of the segue glue   The first is straightforward showing one parameter passed for input  the second for output      Prepare the destination view controller by passing it the input we want it to work on    and the results we will look at when the user has navigated back to this controller s view   -  void prepareForSegue  UIStoryboardSegue   segue sender  id sender         segue destinationViewController           This parameter gives the next controller the data it works on       segueHandoffWithInput self dataForNextController          This parameter allows the next controller to pass back results         by virtue of both controllers having a pointer to the same object       andResults self resultsFromNextController       This second example shows passing a callback block for the second argument   I like using blocks because it keeps the relevant details close together in the source - the higher level source      Prepare the destination view controller by passing it the input we want it to work on    and the callback when it has done its work   -  void prepareForSegue  UIStoryboardSegue   segue sender  id sender         segue destinationViewController           This parameter gives the next controller the data it works on       segueHandoffWithInput self dataForNextController          This parameter allows the next controller to pass back results       resultsBlock   id results                This callback could be as involved as you like              It can use Grand Central Dispatch to have work done on another thread for example           self setResultsFromNextController results

User · Answer

You can create a push segue from the source viewcontroller to the destination viewcontroller and give an identifier name like below   You have to perform a segue from didselectRowAt like this  func tableView   tableView  UITableView  didSelectRowAt indexPath  IndexPath        performSegue withIdentifier   quot segue quot   sender  self     And you can pass the array of the selected item from the below function  override func prepare for segue  UIStoryboardSegue  sender  Any         let index   CategorytableView indexPathForSelectedRow     let indexNumber   index  row     print indexNumber       let VC   segue destination as  AddTransactionVC     VC val   CategoryData indexNumber        Here you can pass the entire array instead of an array element     And you have to check the value in viewdidload of destination viewcontroller and then store it into the database  override func viewDidLoad      if val     quot  quot           btnSelectCategory setTitle val  for   normal

User · Answer

I have seen a lot of people over complicating this using the didSelectRowAtPath method  I am using Core Data in my example  -  void tableView  UITableView   tableView didSelectRowAtIndexPath  NSIndexPath   indexPath          This solution is for using Core Data     YourCDEntityName   value    YourCDEntityName     self fetchedResultsController  objectAtIndexPath  indexPath        YourSecondViewController   details    self storyboard instantiateViewControllerWithIdentifier   quot nameOfYourSecondVC quot       Make sure in storyboards you give your second VC an identifier         Make sure you declare your value in the second view controller     details selectedValue   value          Now that you have said to pass value all you need to do is change views      self navigationController pushViewController  details animated YES       Four lines of code inside the method and you are done

User · Answer

I find simplest and most elegant version with passing blocks  Let s name view controller that waits for returned data as  quot A quot  and returning view controller as  quot B quot   In this example we want to get 2 values  first of Type1 and second of Type2  Assuming we use Storyboard  first controller sets callback block  for example during segue preparation  -  void prepareForSegue  UIStoryboardSegue   segue sender  id sender       if   segue destinationViewController isKindOfClass  BViewController class                  BViewController  viewController   segue destinationViewController           viewController callback     Type1  value1  Type2  value2                   optionally  close B                self navigationController popViewControllerAnimated YES                   let s do some action after with returned values             action1 value1               action2 value2                        and  quot B quot  view controller should declare callback property  BViewController h     it is important to use  quot copy quot   property  copy  void  callback  Type1  value1  Type2  value2    Than in implementation file BViewController m after we have desired values to return our callback should be called  if  self callback      self callback value1  value2    One thing to remember is that using block often needs to manage strong and   weak references  like explained here

User · Answer

I am currently contributing to an open source solution to this problem through a project called MCViewFactory  which may be found here  Manticore iOS View Factory The idea is imitate Android s intent paradigm  using a global factory to manage which view you are looking at and using  quot intents quot  to switch and pass data between views  All the documentation is on the GitHub page  but here are some highlights  You setup all your views in  XIB files and register them in the app delegate  while initializing the factory     Register activities  MCViewFactory  factory    MCViewFactory sharedFactory       The following two lines are optional   factory registerView   quot YourSectionViewController quot     Now  in your view controller  VC   anytime you want to move to a new VC and pass data  you create a new intent and add data to its dictionary  savedInstanceState   Then  just set the current intent of factory  MCIntent  intent    MCIntent intentWithSectionName   quot YourSectionViewController quot     intent setAnimationStyle UIViewAnimationOptionTransitionFlipFromLeft     intent savedInstanceState  setObject   quot someValue quot  forKey   quot yourKey quot      intent savedInstanceState  setObject   quot anotherValue quot  forKey   quot anotherKey quot             MCViewModel sharedModel  setCurrentSection intent    All of your views that conform to this need to be subclasses of MCViewController  which allow you to override the new onResume  method  allowing you access to the data you ve passed in  - void onResume  MCIntent   intent       NSObject  someValue    intent savedInstanceState objectForKey   quot yourKey quot        NSObject  anotherValue    intent savedInstanceState objectForKey   quot anotherKey quot                        Ensure the following line is called  especially for MCSectionViewController      super onResume intent

User · Answer

If you want to send data from one to another viewController  here s a way to do it  Say we have viewControllers  viewControllerA and viewControllerB Now in file viewControllerB h  interface viewControllerB   UIViewController      NSString  string    NSArray  array      -  id initWithArray  NSArray a andString  NSString s   In file viewControllerB m   import  quot viewControllerB h quot    implementation viewControllerB  -  id initWithArray  NSArray a andString  NSString s       array     NSArray alloc  init      array   a      string     NSString alloc  init      string   s      In file viewControllerA m   import  quot viewControllerA h quot   import  quot viewControllerB h quot    implementation viewControllerA  -  void someMethod      someArray    NSArray arrayWithObjects   quot One quot     quot Two quot     quot Three quot   nil     someString    NSString stringWithFormat   quot Hahahahaha quot       viewControllerB  vc     viewControllerB alloc  initWithArray someArray andString someString       self navigationController pushViewController vc animated YES      vc release      So this is how you can pass data from viewControllerA to viewControllerB without setting any delegate

User · Answer

Swift 5 Well Matt Price s answer is perfectly fine for passing data  but I am going to rewrite it  in the latest Swift version because I believe new programmers find it quit challenging due to new syntax and methods frameworks  as original post is in Objective-C   There are multiple options for passing data between view controllers   Using Navigation Controller Push Using Segue Using Delegate Using Notification Observer Using Block  I am going to rewrite his logic in Swift with the latest iOS framework   Passing Data through Navigation Controller Push  From ViewControllerA to ViewControllerB  Step 1  Declare variable in ViewControllerB var isSomethingEnabled   false  Step 2  Print Variable in ViewControllerB  ViewDidLoad method override func viewDidLoad         super viewDidLoad          Print value received through segue  navigation push     print  quot Value of  isSomethingEnabled  from ViewControllerA   quot   isSomethingEnabled     Step 3  In ViewControllerA Pass Data while pushing through Navigation Controller if let viewControllerB   UIStoryboard name   quot Main quot   bundle  nil  instantiateViewController withIdentifier   quot ViewControllerB quot   as  ViewControllerB       viewControllerB isSomethingEnabled   true     if let navigator   navigationController           navigator pushViewController viewControllerB  animated  true           So here is the complete code for  ViewControllerA import UIKit  class ViewControllerA  UIViewController         override func viewDidLoad             super viewDidLoad                 MARK  Passing data through navigation PushViewController      IBAction func goToViewControllerB   sender  Any             if let viewControllerB   UIStoryboard name   quot Main quot   bundle  nil  instantiateViewController withIdentifier   quot ViewControllerB quot   as  ViewControllerB               viewControllerB isSomethingEnabled   true             if let navigator   navigationController                   navigator pushViewController viewControllerB  animated  true                                   ViewControllerB import UIKit  class ViewControllerB  UIViewController           MARK   - Variable for Passing Data through Navigation push     var isSomethingEnabled   false      override func viewDidLoad             super viewDidLoad              Print value received through navigation push         print  quot Value of  isSomethingEnabled  from ViewControllerA   quot   isSomethingEnabled             Passing Data through Segue  From ViewControllerA to ViewControllerB  Step 1  Create Segue from ViewControllerA to ViewControllerB and give Identifier   showDetailSegue in Storyboard as shown below  Step 2  In ViewControllerB Declare a viable named isSomethingEnabled and print its value  Step 3  In ViewControllerA pass isSomethingEnabled s value while passing Segue So here is the complete code for  ViewControllerA import UIKit  class ViewControllerA  UIViewController         override func viewDidLoad             super viewDidLoad                 MARK   - - Passing Data through Segue  - -      IBAction func goToViewControllerBUsingSegue   sender  Any            performSegue withIdentifier   quot showDetailSegue quot   sender  nil                Segue Delegate Method     override func prepare for segue  UIStoryboardSegue  sender  Any             if  segue identifier     quot showDetailSegue quot                 let controller   segue destination as  ViewControllerB             controller  isSomethingEnabled   true  passing data                    ViewControllerB import UIKit  class ViewControllerB  UIViewController       var isSomethingEnabled   false      override func viewDidLoad             super viewDidLoad              Print value received through segue         print  quot Value of  isSomethingEnabled  from ViewControllerA   quot   isSomethingEnabled             Passing Data through Delegate  From ViewControllerB to ViewControllerA  Step 1  Declare Protocol ViewControllerBDelegate in the ViewControllerB file  but outside the class protocol ViewControllerBDelegate  NSObjectProtocol           Classes that adopt this protocol MUST define        this method -- and hopefully do something in        that definition      func addItemViewController   controller  ViewControllerB   didFinishEnteringItem item  String      Step 2  Declare Delegate variable instance in ViewControllerB var delegate  ViewControllerBDelegate   Step 3  Send data for delegate inside viewDidLoad method of ViewControllerB delegate  addItemViewController self  didFinishEnteringItem   quot Data for ViewControllerA quot    Step 4  Confirm ViewControllerBDelegate in ViewControllerA class ViewControllerA  UIViewController  ViewControllerBDelegate       to do    Step 5  Confirm that you will implement a delegate in ViewControllerA if let viewControllerB   UIStoryboard name   quot Main quot   bundle  nil  instantiateViewController withIdentifier   quot ViewControllerB quot   as  ViewControllerB       viewControllerB delegate   self  confirming delegate     if let navigator   navigationController           navigator pushViewController viewControllerB  animated  true           Step 6  Implement delegate method for receiving data in ViewControllerA func addItemViewController   controller  ViewControllerB   didFinishEnteringItem item  String         print  quot Value from ViewControllerB s Delegate quot   item      So here is the complete code for  ViewControllerA import UIKit  class ViewControllerA  UIViewController  ViewControllerBDelegate         override func viewDidLoad             super viewDidLoad                 Delegate method     func addItemViewController   controller  ViewControllerB   didFinishEnteringItem item  String             print  quot Value from ViewControllerB s Delegate quot   item               IBAction func goToViewControllerForDelegate   sender  Any             if let viewControllerB   UIStoryboard name   quot Main quot   bundle  nil  instantiateViewController withIdentifier   quot ViewControllerB quot   as  ViewControllerB               viewControllerB delegate   self             if let navigator   navigationController                   navigator pushViewController viewControllerB  animated  true                                   ViewControllerB import UIKit    Protocol decleare protocol ViewControllerBDelegate  NSObjectProtocol          Classes that adopt this protocol MUST define        this method -- and hopefully do something in        that definition      func addItemViewController   controller  ViewControllerB   didFinishEnteringItem item  String      class ViewControllerB  UIViewController       var delegate  ViewControllerBDelegate       override func viewDidLoad             super viewDidLoad              MARK   - - - -  Set Data for Passing Data through Delegate  - - - - - -         delegate  addItemViewController self  didFinishEnteringItem   quot Data for ViewControllerA quot              Passing Data through Notification Observer  From ViewControllerB to ViewControllerA  Step 1  Set and post data in the notification observer in ViewControllerB let objToBeSent    quot Test Message from Notification quot          NotificationCenter default post name  Notification Name  quot NotificationIdentifier quot    object  objToBeSent   Step 2  Add Notification Observer in ViewControllerA NotificationCenter default addObserver self  selector   selector self methodOfReceivedNotification notification     name  Notification Name  quot NotificationIdentifier quot    object  nil   Step 3  Receive Notification data value in ViewControllerA  objc func methodOfReceivedNotification notification  Notification        print  quot Value of notification   quot   notification object     quot  quot      So here is the complete code for  ViewControllerA import UIKit  class ViewControllerA  UIViewController       override func viewDidLoad             super viewDidLoad               Add observer in controller s  where you want to receive data         NotificationCenter default addObserver self  selector   selector self methodOfReceivedNotification notification     name  Notification Name  quot NotificationIdentifier quot    object  nil                MARK  Method for receiving Data through Post Notification      objc func methodOfReceivedNotification notification  Notification            print  quot Value of notification   quot   notification object     quot  quot            ViewControllerB import UIKit  class ViewControllerB  UIViewController        override func viewDidLoad             super viewDidLoad               MARK Set data for Passing Data through Post Notification         let objToBeSent    quot Test Message from Notification quot          NotificationCenter default post name  Notification Name  quot NotificationIdentifier quot    object  objToBeSent             Passing Data through Block  From ViewControllerB to ViewControllerA  Step 1  Declare block in ViewControllerB var authorizationCompletionBlock   Bool - gt           in  Step 2  Set data in block in ViewControllerB if authorizationCompletionBlock    nil       authorizationCompletionBlock  true     Step 3  Receive block data in ViewControllerA    Receiver Block controller  authorizationCompletionBlock     isGranted in     print  quot Data received from Block is   quot   isGranted     So here is the complete code for  ViewControllerA import UIKit  class ViewControllerA  UIViewController         override func viewDidLoad             super viewDidLoad                 MARK Method for receiving Data through Block     override func prepare for segue  UIStoryboardSegue  sender  Any             if  segue identifier     quot showDetailSegue quot                 let controller   segue destination as  ViewControllerB             controller  isSomethingEnabled   true                 Receiver Block             controller  authorizationCompletionBlock     isGranted in                 print  quot Data received from Block is   quot   isGranted                                   ViewControllerB import UIKit  class ViewControllerB  UIViewController           MARK  Variable for Passing Data through Block     var authorizationCompletionBlock   Bool - gt           in       override func viewDidLoad             super viewDidLoad               MARK  Set data for Passing Data through Block         if authorizationCompletionBlock    nil                       authorizationCompletionBlock  true                     You can find complete sample Application at my GitHub Please let me know if you have any question s  on this

User · Answer

A simpler way is here  Just use a global variable  Declare the object or variable needed to pass to the next class  For example  we have two classes - classA and classB respectively  In classA  normally it contains   import  quot classA h quot    interface classA     end   implementation classA  - void viewDidLoad             - void didReceiveMemoryWarning              And classB contains   import  quot classB h quot    interface classB     end   implementation classB  - void viewWillLoad             - void didReceiveMemoryWarning              Now  import the second class classB to classA   import  quot classA h quot   import  quot classB h quot      --- Import classB to classA   interface classA     end   implementation classA  - void viewDidLoad             - void didReceiveMemoryWarning              Now we have a bridge to go to the second class classB  Now  for declaring a variable or object as global  declare it in the  m file of the first class as below  In classA h  import  quot classA h quot   import  quot classB h quot   interface classA     end NSString  temp      ---- Declare any object variable as global   implementation classA  - void viewDidLoad               temp   quot Hello quot             - void didReceiveMemoryWarning              Here the object temp is a global object of class NSString  For accessing the global object or variable in any class  just redeclare the object or variable in the second class  For example  as given below  In classB m  import  quot classB h quot    interface classB     end extern NSString  temp     ----use  extern  keyword for using the global object variable in classB that was declared in classA   implementation classB  - void viewDidLoad               LabeL text temp            - void didReceiveMemoryWarning              Now the value can be accessed by the second class  Simple     This method can be followed for any number of classes  Note  You should import  the h file of the second class to the first class  But there isn t any need to import the  h file of the first class to the second class  Remember the bridge  If there is a bridge  it should be able to go on both sides

User · Answer

Using Notification Center For Swift 3 let imageDataDict  String  UIImage      quot image quot   image      Post a notification NotificationCenter default post name  NSNotification Name rawValue   quot notificationName quot    object  nil  userInfo  imageDataDict      default  is now a property  not a method call     Register to receive notification in your class NotificationCenter default addObserver self  selector   selector self showSpinningWheel       name  NSNotification Name rawValue   quot notificationName quot    object  nil      Handle notification func showSpinningWheel   notification  NSNotification        print notification userInfo     quot  quot       if let dict   notification userInfo as NSDictionary            if let id   dict  quot image quot   as  UIImage                  Do something with your image                    For Swift 4 let imageDataDict  String  UIImage      quot image quot   image      Post a notification NotificationCenter default post name  NSNotification Name rawValue   quot notificationName quot    object  nil  userInfo  imageDataDict      default  is now a property  not a method call     Register to receive notification in your class NotificationCenter default addObserver self  selector   selector self showSpinningWheel       name  NSNotification Name rawValue   quot notificationName quot    object  nil      Handle notification  objc func showSpinningWheel   notification  NSNotification        print notification userInfo     quot  quot       if let dict   notification userInfo as NSDictionary            if let id   dict  quot image quot   as  UIImage                  Do something with your image

User · Answer

There are 3 types for passing data one ViewController to another   ViewController     Programatically Segue UserDefaults   Demo Project Link Here - https   github com kamanijasmin13 Swift-Pass-data-between-viewcontrollers  Programatically   Segue   UserDefaults   Demo Project Link Here - https   github com kamanijasmin13 Swift-Pass-data-between-viewcontrollers

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This question seems to be very popular here on Stack  Overflow so I thought I would try and give a better answer to help out people starting in the world of iOS like me  I hope this answer is clear enough for people to understand and that I have not missed anything  Passing Data Forward Passing data forward to a view controller from another view controller  You would use this method if you wanted to pass an object value from one view controller to another view controller that you may be pushing on to a navigation stack  For this example  we will have ViewControllerA and ViewControllerB To pass a BOOL value from ViewControllerA to ViewControllerB we would do the following   in ViewControllerB h create a property for the BOOL   property  nonatomic  assign  BOOL isSomethingEnabled    in ViewControllerA you need to tell it about ViewControllerB so use an   import  quot ViewControllerB h quot     Then where you want to load the view  for example  didSelectRowAtIndex or some IBAction  you need to set the property in ViewControllerB before you push it onto the navigation stack      ViewControllerB  viewControllerB     ViewControllerB alloc  initWithNib   quot ViewControllerB quot  bundle nil       viewControllerB isSomethingEnabled   YES       self pushViewController viewControllerB animated YES    This will set isSomethingEnabled in ViewControllerB to BOOL value YES  Passing Data Forward using Segues If you are using Storyboards you are most likely using segues and will need this procedure to pass data forward  This is similar to the above but instead of passing the data before you push the view controller  you use a method called - void prepareForSegue  UIStoryboardSegue   segue sender  id sender  So to pass a BOOL from ViewControllerA to ViewControllerB we would do the following   in ViewControllerB h create a property for the BOOL   property  nonatomic  assign  BOOL isSomethingEnabled    in ViewControllerA you need to tell it about ViewControllerB  so use an   import  quot ViewControllerB h quot    Create the segue from ViewControllerA to ViewControllerB on the storyboard and give it an identifier  In this example we ll call it  quot showDetailSegue quot   Next  we need to add the method to ViewControllerA that is called when any segue is performed  Because of this we need to detect which segue was called and then do something  In our example  we will check for  quot showDetailSegue quot  and if that s performed  we will pass our BOOL value to ViewControllerB  - void prepareForSegue  UIStoryboardSegue   segue sender  id sender       if  segue identifier isEqualToString   quot showDetailSegue quot              ViewControllerB  controller    ViewControllerB   segue destinationViewController           controller isSomethingEnabled   YES               If you have your views embedded in a navigation controller  you need to change the method above slightly to the following     - void prepareForSegue  UIStoryboardSegue   segue sender  id sender          if  segue identifier isEqualToString   quot showDetailSegue quot                 UINavigationController  navController    UINavigationController   segue destinationViewController              ViewControllerB  controller    ViewControllerB   navController topViewController              controller isSomethingEnabled   YES                   This will set isSomethingEnabled in ViewControllerB to BOOL value YES  Passing Data Back To pass data back from ViewControllerB to ViewControllerA you need to use Protocols and Delegates or Blocks  the latter can be used as a loosely coupled mechanism for callbacks  To do this we will make ViewControllerA a delegate of ViewControllerB  This allows ViewControllerB to send a message back to ViewControllerA enabling us to send data back  For ViewControllerA to be a delegate of ViewControllerB it must conform to ViewControllerB s protocol which we have to specify  This tells ViewControllerA which methods it must implement   In ViewControllerB h  below the  import  but above  interface you specify the protocol    class ViewControllerB     protocol ViewControllerBDelegate  lt NSObject gt   -  void addItemViewController  ViewControllerB   controller didFinishEnteringItem  NSString   item    end   Next still in the ViewControllerB h  you need to set up a delegate property and synthesize in ViewControllerB m   property  nonatomic  weak  id  lt ViewControllerBDelegate gt  delegate    In ViewControllerB we call a message on the delegate when we pop the view controller   NSString  itemToPassBack     quot Pass this value back to ViewControllerA quot     self delegate addItemViewController self didFinishEnteringItem itemToPassBack     That s it for ViewControllerB  Now in ViewControllerA h  tell ViewControllerA to import ViewControllerB and conform to its protocol    import  quot ViewControllerB h quot     interface ViewControllerA   UIViewController  lt ViewControllerBDelegate gt    In ViewControllerA m implement the following method from our protocol  -  void addItemViewController  ViewControllerB   controller didFinishEnteringItem  NSString   item         NSLog   quot This was returned from ViewControllerB    quot   item        Before pushing viewControllerB to navigation stack we need to tell  ViewControllerB that ViewControllerA is its delegate  otherwise we will get an error   ViewControllerB  viewControllerB     ViewControllerB alloc  initWithNib   quot ViewControllerB quot  bundle nil    viewControllerB delegate   self    self navigationController  pushViewController viewControllerB animated YES       References  Using Delegation to Communicate With Other View Controllers in the View Controller Programming Guide Delegate Pattern  NSNotification center It s another way to pass data     Add an observer in controller s  where you want to receive data   NSNotificationCenter defaultCenter  addObserver self selector  selector handleDeepLinking   name   quot handleDeepLinking quot  object nil    - void  handleDeepLinking  NSNotification    notification       id someObject   notification object    Some custom object that was passed with notification fire        Post notification id someObject   NSNotificationCenter defaultCenter postNotificationName   quot handleDeepLinking quot  object someObject    Passing Data back from one class to another  A class can be any controller  Network session manager  UIView subclass or any other class  Blocks are anonymous functions  This example passes data from Controller B to Controller A Define a block  property void  selectedVoucherBlock  NSString        in ContollerA h  Add block handler  listener  Where you need a value  for example  you need your API response in ControllerA or you need ContorllerB data on A     In ContollerA m  -  void viewDidLoad        super viewDidLoad         unsafe unretained typeof self  weakSelf   self      self selectedVoucherBlock     NSString  voucher            weakSelf- gt someLabel text   voucher            Go to Controller B UIStoryboard  storyboard    UIStoryboard storyboardWithName   quot Main quot  bundle nil   ControllerB  vc    storyboard instantiateViewControllerWithIdentifier   quot ControllerB quot    vc sourceVC   self       self navigationController pushViewController vc animated NO    Fire block - void tableView  UITableView   tableView didSelectRowAtIndexPath   NSIndexPath   indexPath       NSString  voucher   vouchersArray indexPath row       if  sourceVC selectVoucherBlock            sourceVC selectVoucherBlock voucher              self navigationController popToViewController sourceVC animated YES      Another Working Example for Blocks

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In my case  I used a singleton class which could work as a global object allowing accesses to the data from almost everywhere in the app  The first thing is to build a singleton class  Please refer to the page What should my Objective-C singleton look like   And to make the object globally accessible  I simply imported it in appName Prefix pch which was for applying import statement in every classes  To access this object and to use it  I simply implemented a class method to return the shared instance  which contains its own variables

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If you want to pass data from one controller to other  try this code  File FirstViewController h  property  nonatomic  retain  NSString  str   SecondViewController h  property  nonatomic  retain  NSString  str1   File FirstViewController m -  void viewDidLoad              Message for the second SecondViewController      self str     quot text message quot          super viewDidLoad         - IBAction ButtonClicked       SecondViewController  secondViewController     SecondViewController alloc  initWithNibName   quot SecondViewController quot  bundle nil      secondViewController str1   str     self navigationController pushViewController secondViewController animated YES

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An Apple way to do this is to use Segues  You need to use the prepareForSegue   function  There are lots of great tutorials around  and here is one  Unleash Your Inner App Developer Part 21  Passing Data Between Controllers Also  read up the Apple documentation on using segues  Using Segues

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With a Swift slant and want a bare-bones example  here is my go-to method for passing data if you are using a segue to get around  It is similar to the above but without the buttons  labels and such  Just simply passing data from one view to the next  Setup The Storyboard There are three parts   The Sender The Segue The Receiver  This is a very simple view layout with a segue between them     Here is the setup for the sender    Here is the setup for the receiver     Lastly  the setup for the segue     The View Controllers We are keeping this simple so no buttons and not actions  We are simply moving data from the sender to the receiver when the application loads and then outputting the transmitted value to the console  This page takes the initially loaded value and passes it along  import UIKit   class ViewControllerSender  UIViewController           THE STUFF - put some information into a variable     let favoriteMovie    quot Ghost Busters quot       override func viewDidAppear animated  Bool               PASS IDENTIFIER - go to the receiving view controller          self performSegueWithIdentifier  quot goToReciever quot   sender  self             override func prepareForSegue segue  UIStoryboardSegue  sender  AnyObject                 GET REFERENCE -    to the receiver view          var viewControllerReceiver   segue destinationViewController as  ViewControllerReceiver             PASS STUFF - pass the variable along to the target          viewControllerReceiver  yourFavMovie   self favoriteMovie           This page just sends the value of the variable to the console when it loads  By this point  our favorite movie should be in that variable  import UIKit  class ViewControllerReceiver  UIViewController           Basic empty variable waiting for you to pass in your fantastic favorite movie      var yourFavMovie    quot  quot       override func viewDidLoad             super viewDidLoad               And now we can view it in the console          println  quot The Movie is   self yourFavMovie  quot             That is how you can tackle it if you want to use a segue and you don t have your pages under a navigation controller  Once it is run  it should switch to the receiver view automatically and pass the value from the sender to the receiver  displaying the value in the console

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If you want to pass data from ViewControlerOne to ViewControllerTwo  try these    Do these in ViewControlerOne h    property  nonatomic  strong  NSString  str1   Do these in ViewControllerTwo h    property  nonatomic  strong  NSString  str2   Synthesize str2 in ViewControllerTwo m   interface ViewControllerTwo     end  implementation ViewControllerTwo  synthesize str2   Do these in ViewControlerOne m   -  void viewDidLoad        super viewDidLoad          Data or string you wants to pass in ViewControllerTwo       self str1     quot hello world quot       O the buttons click event  do this  - IBAction ButtonClicked        Navigation on buttons click event from ViewControlerOne to ViewControlerTwo with transferring data or string     ViewControllerTwo  objViewTwo    self storyboard instantiateViewControllerWithIdentifier   quot ViewControllerTwo quot      obj str2   str1     self navigationController pushViewController  objViewTwo animated YES      Do these in ViewControllerTwo m  -  void viewDidLoad      super viewDidLoad     NSLog   quot    quot   str2

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This is a really great tutorial for anyone that wants one  Here is the example code  -  void prepareForSegue  UIStoryboardSegue   segue sender  id sender       if   segue identifier isEqualToString   quot myIdentifer             NSIndexPath  indexPath    self tableView indexPathForSelectedRow           myViewController  destViewController   segue destinationViewController          destViewController name    object objectAtIndex indexPath row

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There are many answers to this questions offering many different ways to perform view controller communication that would indeed work  but I don t see anywhere mentioned which one are actually best to use and which ones to avoid   In practice  in my opinion only a few solutions are recommended    To pass data forward    override the prepare for sender   method of UIViewController when using a storyboard and segues pass data through an initializer or through properties when performing view controller transitions thtough code  To pass data backwards   update the app shared state  which you can pass forward between view controllers with either one of the methods above  use delegation use an unwind segue    Solutions I recommend NOT to use    Referencing the previous controller directly instead of using delegation Sharing data through a singleton Passing data through the app delegate Sharing data through the user defaults Passing data through notifications   These solutions  although working in the short term  introduce too many dependencies that will garble the architecture of the app and create more problems later   For those interested  I wrote some articles that address these points more in depth and highlight the various drawbacks    How iOS View Controllers Communicate With Each Other How to Structure the Code of iOS Apps Understanding the Core Architectural Principles of iOS Development with a Practical Example

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Swift There are tons and tons of explanations here and around Stack  Overflow  but if you are a beginner just trying to get something basic to work  try watching this YouTube tutorial  It s what helped me to finally understand how to do it    YouTube tutorial  How to send data through segue  Swift   Passing data forward to the next View Controller The following is an example based on the video  The idea is to pass a string from the text field in the First View Controller to the label in the Second View Controller   Create the storyboard layout in the Interface Builder  To make the segue  you just Control click on the button and drag over to the Second View Controller  First View Controller The code for the First View Controller is import UIKit  class FirstViewController  UIViewController         IBOutlet weak var textField  UITextField          This function is called before the segue     override func prepare for segue  UIStoryboardSegue  sender  Any                 Get a reference to the second view controller         let secondViewController   segue destination as  SecondViewController             Set a variable in the second view controller with the String to pass         secondViewController receivedString   textField text            Second View Controller And the code for the Second View Controller is import UIKit  class SecondViewController  UIViewController         IBOutlet weak var label  UILabel          This variable will hold the data being passed from the First View Controller     var receivedString    quot  quot       override func viewDidLoad             super viewDidLoad               Used the text from the First View Controller to set the label         label text   receivedString           Don t forget  Hook up the outlets for the UITextField and the UILabel  Set the first and second View Controllers to the appropriate Swift files in Interface Builder   Passing data back to the previous View Controller To pass data back from the second view controller to the first view controller  you use a protocol and a delegate  This video is a very clear walk though of that process   YouTube tutorial  iOS Swift Basics Tutorial  Protocols and Delegates But also read this post to make sure you don t get into a strong reference cycle   The following is an example based on the video  with a few modifications    Create the storyboard layout in the Interface Builder  Again  to make the segue  you just Control drag from the button to the Second View Controller  Set the segue identifier to showSecondViewController  Also  don t forget to hook up the outlets and actions using the names in the following code  First View Controller The code for the First View Controller is import UIKit  class FirstViewController  UIViewController  DataEnteredDelegate         IBOutlet weak var label  UILabel       override func prepare for segue  UIStoryboardSegue  sender  Any             if segue identifier     quot showSecondViewController quot                let secondViewController   segue destination as  SecondViewController             secondViewController delegate   self                      func userDidEnterInformation info  String            label text   info          Note the use of our custom DataEnteredDelegate protocol  Second View Controller and Protocol The code for the second view controller is import UIKit     Protocol used for sending data back protocol DataEnteredDelegate  AnyObject       func userDidEnterInformation info  String     class SecondViewController  UIViewController           Making this a weak variable  so that it won t create a strong reference cycle     weak var delegate  DataEnteredDelegate    nil       IBOutlet weak var textField  UITextField        IBAction func sendTextBackButton sender  AnyObject                Call this method on whichever class implements our delegate protocol         delegate  userDidEnterInformation info  textField text               Go back to the previous view controller             self navigationController  popViewController animated  true           Note that the protocol is outside of the View Controller class  That s it  Running the app now  you should be able to send data back from the second view controller to the first

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There are many solutions for passing data in Swift  Passing data forward My two favorite ways to pass data forwardly is dependency injection  DI  and Property Observers Dependency Injection class CustomView   UIView       init   with model   Model               Do what you want with data          Property Observers class CustomView   UIView       var model   Model            didSet                  Do what you want with data after assign data to model                   willSet                  Do what you want with data before assign data to model                    Passing data backward Also favorite ways to passing data to the previous VC view  Protocol and Delegate protocol CustomViewDelegate   class       func addItemViewController   with data  Model      weak var delegate   CustomViewDelegate   class AnotherCustomView  UIView         let customView   AnotherCustomView         init              customView delegate   self           extention AnotherCustomView   CustomViewDelegate       func addItemViewController   with data  Model                Do what you want with data          Closure class AnotherCustomView   UIView        init addItem   escaping    value   Model   - gt                   Do what you want with data           class CustomView   UIView        init             let customView   AnotherCustomView    weak self  model in                Do what you want with data

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Passing data back from ViewController 2  destination  to viewController 1  source  is the more interesting thing  Assuming you use storyBoard  these are all the ways I found out   Delegate Notification User defaults Singleton  Those were discussed here already  I found there are more ways  Using Block callbacks  Use it in the prepareForSegue method in the VC1 NextViewController  destinationVC    NextViewController    segue destinationViewController   destinationVC setDidFinishUsingBlockCallback   NextViewController  destinationVC        self blockLabel text   destination blockTextField text       Using storyboards Unwind  Exit  Implement a method with a UIStoryboardSegue argument in  VC 1 like this one  - IBAction UnWindDone  UIStoryboardSegue   segue      In the storyBoard  hook the  quot return quot  button to the green Exit button  Unwind  of the vc  Now you have a segue that  quot goes back quot  so you can use the destinationViewController property in the prepareForSegue of VC2 and change any property of VC1 before it goes back   Another option of using storyboards Undwind  Exit   - you can use the method you wrote in VC1  - IBAction UnWindDone  UIStoryboardSegue   segue        NextViewController  nextViewController   segue sourceViewController       self unwindLabel text   nextViewController unwindPropertyPass        And in the prepareForSegue of VC1 you can change any property you want to share  In both unwind options  you can set the tag property of the button and check it in the prepareForSegue

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There are multiple methods for sharing data    You can always share data using NSUserDefaults  Set the value you want to share with respect to a key of your choice and get the value from NSUserDefault associated to that key in the next view controller      NSUserDefaults standardUserDefaults  setValue value forKey key    NSUserDefaults standardUserDefaults  objectForKey key   You can just create a property in viewcontrollerA  Create an object of viewcontrollerA in viewcontrollerB and assign the desired value to that property  You can also create custom delegates for this

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I recommend blocks closures and custom constructors   Suppose you have to pass string from FirstViewController to SecondViewController   Your First View Controller    class FirstViewController   UIViewController        func moveToViewControllerB              let second screen   SecondViewController screen string   DATA TO PASS   call back                 weak self   updated data  in                This closure will be called by second view controller when it updates something                    self navigationController  pushViewController second screen  animated  true              Your Second View Controller  class SecondViewController   UIViewController        var incoming string   String      var call back     String  - gt  Void        class func screen string  String   call back     String  - gt  Void    - gt  SecondViewController            let me   SecondViewController nibName  String describing  self   bundle  Bundle main           me incoming string   string         me call back   call back         return me               Suppose its called when you have to update FirstViewController with new data      func updatedSomething                Executing block that is implemented assigned by the FirstViewController          self call back   UPDATED DATA

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There is some good information in many of the answers given  but none address the question fully  The question asks about passing information between view controllers  The specific example given asks about passing information between views  but given the self-stated newness to iOS  the original poster likely meant between viewControllers  not between views  without any involvement from the ViewControllers   It seems that all the answers focus on two view controllers  but what if the app evolves to need to involve more than two view controllers in the information exchange  The original poster also asked about Singletons and the use of the AppDelegate  These questions need to be answered  To help anyone else looking at this question  who wants a full answer  I m going to attempt to provide it  Application Scenarios Rather than having a highly hypothetical  abstract discussion  it helps to have concrete applications in mind  To help define a two-view-controller situation and a more-than-two-view-controller situation  I am going to define two concrete application scenarios  Scenario one  maximum two view controllers ever need to share information  See diagram one   There are two view controllers in the application  There is a ViewControllerA  Data Entry Form   and View Controller B  Product List   The items selected in the product list must match the items displayed in the text box in the data entry form  In this scenario  ViewControllerA and ViewControllerB must communicate directly with each other and no other view controllers  Scenario two  more than two view controllers need to share the same information  See diagram two   There are four view controllers in the application  It is a tab-based application for managing home inventory  Three view controllers present differently filtered views of the same data   ViewControllerA - Luxury Items ViewControllerB - Non-insured Items ViewControllerC - Entire Home Inventory ViewControllerD - Add New Item Form  Any time an individual item is created or edited  it must also synchronize with the other view controllers  For example  if we add a boat in ViewControllerD  but it is not yet insured  then the boat must appear when the user goes to ViewControllerA  Luxury Items   and also ViewControllerC  Entire Home Inventory   but not when the user goes to ViewControllerB  Non-insured Items   We need be concerned with not only adding new items  but also deleting items  which may be allowed from any of the four view controllers   or editing existing items  which may be allowed from the  quot Add New Item Form quot   repurposing the same for editing   Since all the view controllers do need to share the same data  all four view controllers need to remain in synchronization  and therefore there needs to be some sort of communication to all other view controllers  whenever any single view controller changes the underlying data  It should be fairly obvious that we do not want each view controller communicating directly with each other view controller in this scenario  In case it is not obvious  consider if we had 20 different view controllers  rather than just 4   How difficult and error-prone would it be to notify each of the other 19 view controllers any time one view controller made a change  The Solutions  Delegates and the Observer Pattern  and Singletons In scenario one  we have several viable solutions  as other answers have given  segues delegates setting properties on view controllers directly NSUserDefaults  actually a poor choice   In scenario two  we have other viable solutions   Observer Pattern Singletons  A singleton is an instance of a class  that instance being the only instance in existence during its lifetime  A singleton gets its name from the fact that it is the single instance  Normally developers who use singletons have special class methods for accessing them     HouseholdInventoryManager   sharedManager        static dispatch once t onceQueue      static HouseholdInventoryManager   sharedInstance          dispatch once is guaranteed to only be executed        once in the lifetime of the application     dispatch once  amp onceQueue              sharedInstance     self alloc  init               return  sharedInstance     Now that we understand what a singleton is  let s discuss how a singleton fits into the observer pattern  The observer pattern is used for one object to respond to changes by another object  In the second scenario  we have four different view controllers  who all want to know about changes to the underlying data  The  quot underlying data quot  should belong to a single instance  a singleton  The  quot know about changes quot  is accomplished by observing changes made to the singleton  The home inventory application would have a single instance of a class which is designed to manage a list of inventory items  The manager would manage a collection of household items  The following is a class definition for the data manager   import  lt Foundation Foundation h gt    class JGCHouseholdInventoryItem    interface HouseholdInventoryManager   NSObject      The global singleton for accessing application data        HouseholdInventoryManager   sharedManager    -  NSArray    entireHouseholdInventory  -  NSArray    luxuryItems  -  NSArray    nonInsuredItems   -  void  addHouseholdItemToHomeInventory  JGCHouseholdInventoryItem  item  -  void  editHouseholdItemInHomeInventory  JGCHouseholdInventoryItem  item  -  void  deleteHoueholdItemFromHomeInventory  JGCHouseholdInventoryItem  item   end  When the collection of home inventory items changes  the view controllers need to be made aware of this change  The class definition above does not make it obvious how this will happen  We need to follow the observer pattern  The view controllers must formally observe the sharedManager  There are two ways to observe another object   Key-Value-Observing  KVO  NSNotificationCenter   In scenario two  we do not have a single property of the HouseholdInventoryManager which could be observed using KVO  Because we do not have a single property which is easily observable  the observer pattern  in this case  must be implemented using NSNotificationCenter  Each of the four view controllers would subscribe to notifications  and the sharedManager would send notifications to the notification center when appropriate  The inventory manager does not need to know anything about the view controllers or instances of any other classes which may be interested in knowing when the collection of inventory items changes  the NSNotificationCenter takes care of these implementation details  The View Controllers simply subscribe to notifications  and the data manager simply posts notifications  Many beginner programmers take advantage of the fact that there is always exactly one Application Delegate in the lifetime of the application  which is globally accessible  Beginning programmers use this fact to stuff objects and functionality into the appDelegate as a convenience for access from anywhere else in the application  Just because the AppDelegate is a singleton doesn t mean it should replace all other singletons  This is a poor practice as it places too much burden on one class  breaking good object-oriented practices  Each class should have a clear role that is easily explained  often just by the name of the class  Any time your Application Delegate starts to get bloated  start to remove functionality into singletons  For example  the Core Data Stack should not be left in the AppDelegate  but should instead be put in its own class  a coreDataManager class  References  Managing Data Flow Between View Controllers Passing Data Between View Controllers Asynchronous JSON Requests in Objective-C

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You can save data in an App delegate to access it across view controllers in your application  All you have to do is create a shared instance of an app delegate  AppDelegate  appDelegate    AppDelegate    UIApplication sharedApplication  delegate   For Example If you declare a NSArray object  arrayXYZ  then you can access it in any view controller by appDelegate arrayXYZ

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NewsViewController  -  void tableView  UITableView   tableView didSelectRowAtIndexPath  NSIndexPath   indexPath      tbl View deselectRowAtIndexPath indexPath animated YES     News  newsObj    newstitleArr objectAtIndex indexPath row     NewsDetailViewController  newsDetailView     NewsDetailViewController alloc  initWithNibName   NewsDetailViewController  bundle nil      newsDetailView newsHeadlineStr   newsObj newsHeadline      self navigationController pushViewController newsDetailView animated YES       NewsDetailViewController h   interface NewsDetailViewController   UIViewController  property nonatomic retain  NSString  newsHeadlineStr   end   NewsDetailViewController m   synthesize newsHeadlineStr

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The M in MVC is for  quot Model quot  and in the MVC paradigm the role of model classes is to manage a program s data  A model is the opposite of a view -- a view knows how to display data  but it knows nothing about what to do with data  whereas a model knows everything about how to work with data  but nothing about how to display it  Models can be complicated  but they don t have to be -- the model for your app might be as simple as an array of strings or dictionaries  The role of a controller is to mediate between view and model  Therefore  they need a reference to one or more view objects and one or more model objects  Let s say that your model is an array of dictionaries  with each dictionary representing one row in your table  The root view for your app displays that table  and it might be responsible for loading the array from a file  When the user decides to add a new row to the table  they tap some button and your controller creates a new  mutable  dictionary and adds it to the array  In order to fill in the row  the controller creates a detail view controller and gives it the new dictionary  The detail view controller fills in the dictionary and returns  The dictionary is already part of the model  so nothing else needs to happen

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There are various ways by which data can be received by a different class in iOS  For example -  Direct initialization after the allocation of another class  Delegation - for passing data back Notification - for broadcasting data to multiple classes at a single time Saving in NSUserDefaults - for accessing it later Singleton classes Databases and other storage mechanisms  like p-list files  etc   But for the simple scenario of passing a value to a different class whose allocation is done in the current class  the most common and preferred method would be the direct setting of values after allocation  This is done as follows  We can understand it using two controllers - Controller1 and Controller2 Suppose in Controller1 class you want to create the Controller2 object and push it with a String value being passed  This can be done as this  -  void pushToController2        Controller2  obj     Controller2 alloc  initWithNib   quot Controller2 quot  bundle nil        obj passValue   quot String quot         self pushViewController obj animated YES      In the implementation of the Controller2 class there will be this function as   interface Controller2    NSObject   property  nonatomic  strong  NSString  stringPassed    end   implementation Controller2   synthesize stringPassed    stringPassed   -  void  passValue  NSString   value         stringPassed   value     Or self stringPassed   value     end  You can also directly set the properties of the Controller2 class in the similar way as this  -  void pushToController2        Controller2  obj     Controller2 alloc  initWithNib   quot Controller2 quot  bundle nil        obj setStringPassed   quot String quot         self pushViewController obj animated YES      To pass multiple values  you can use the multiple parameters like  Controller2  obj     Controller2 alloc  initWithNib   quot Controller2 quot  bundle nil    obj passValue     String1    andValues objArray withDate date    Or if you need to pass more than three parameters which are related to a common feature  you can store the values in a model class and pass that modelObject to the next class ModelClass  modelObject     ModelClass alloc  init   modelObject property1    property1  modelObject property2    property2  modelObject property3    property3   Controller2  obj     Controller2 alloc  initWithNib   quot Controller2 quot  bundle nil    obj passmodel  modelObject    So in short  if you want to -  set the private variables of the second class initialise the values by calling a custom function and passing the values  setProperties do it by directlyInitialising it using the setter method  pass more that 3-4 values related to each other in some manner  then create a model class and set values to its object and pass the object using any of the above process

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Delegation is the only one solution to perform such operations when you are using  xib files  However  all previous answers are for storyboard for  xibs files   You need to use delegation  That s the only solution you can use  Another solution is use the singleton class pattern  Initialize it once and use it in your entire app

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You have to always follow the MVC concept when creating apps for iOS  There are two scenarios where you may want to pass data from a ViewController to another   When there is an  quot A quot  ViewContoller in the hierarchy and you want to send some data to  quot B quot  which is the next viewcontroller  In this case you have to use Segue  Just set an identifier for the segue and then in the  quot A quot  VC  write the following code  override func prepare for segue  UIStoryboardSegue  sender  Any         if segue identifier     quot A to B segue identifier quot            let bViewController   segue destination as  UIDocumentBrowserViewController         bViewController data   someData           When there is an A which opened B upon itself as modal  or embed   Now the B viewcontroller should be blind about its parent  So the best way to send data back to A is to use Delegation  Create a delegate protocol in the B viewcontroller and a delegate property  So B will report  send data back  to it s delegate  In the A viewcontroller  we implement the B viewcontroller s delegate protocol and will set self as the delegate property of B viewcontroller in prepare forSegue   method    This is how it should be implemented correctly

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To send the data from one view controller  VC  to the other  use this simple approach  YourNextVC  nxtScr    YourNextVC   self storyboard  instantiateViewControllerWithIdentifier   quot YourNextVC quot     Set this identifier from your storyboard  nxtScr comingFrom     quot PreviousScreen quot l  self navigationController nxtScr animated YES

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For SwiftUI  Think of  EnvironmentObject as a smarter  simpler way of using  ObservedObject on lots of views  Rather than creating some data in view A  then passing it to view B  then view C  then view D before finally using it  you can create it in view and put it into the environment so that views B  C  and D will automatically have access to it   Note  Environment objects must be supplied by an ancestor view     if SwiftUI can   t find an environment object of the correct type you   ll get a crash  This applies for previews too  so be careful   As an example  here   s an observable object that stores user settings   class UserSettings  ObservableObject         Published var score   0

[ios] Passing data between view controllers

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