Delegates in swift

Question

How does one go about making a delegate  i e  NSUserNotificationCenterDelegate in swift

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DELEGATES IN SWIFT 2 I am explaining with example of Delegate with two viewControllers In this case  SecondVC Object is sending data back to first View Controller  Class with Protocol Declaration protocol  getDataDelegate        func getDataFromAnotherVC temp  String      import UIKit class SecondVC  UIViewController        var delegateCustom   getDataDelegate      override func viewDidLoad             super viewDidLoad               override func didReceiveMemoryWarning             super didReceiveMemoryWarning              Dispose of any resources that can be recreated             IBAction func backToMainVC sender  AnyObject            calling method defined in first View Controller with Object         self delegateCustom  getDataFromAnotherVC temp   quot I am sending data from second controller to first view controller Its my first delegate example  I am done with custom delegates  quot           self navigationController  popViewControllerAnimated true                In First ViewController Protocol conforming is done here  class ViewController  UIViewController  getDataDelegate  Protocol method definition in First View Controller ViewController  func getDataFromAnotherVC temp   String         dataString from SecondVC    lblForData text   dataString    During push the SecondVC from First View Controller  ViewController  let objectPush   SecondVC   objectPush delegateCustom   self self navigationController pushViewController objectPush  animated  true

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Here s a gist I put together  I was wondering the same and this helped improve my understanding  Open this up in an Xcode Playground to see what s going on   protocol YelpRequestDelegate       func getYelpData   - gt  AnyObject     func processYelpData data  NSData  - gt  NSData    class YelpAPI       var delegate  YelpRequestDelegate       func getData             println  data being retrieved              let data  AnyObject    delegate  getYelpData              func processYelpData data  NSData            println  data being processed              let data   delegate  processYelpData data           class Controller  YelpRequestDelegate       init             var yelpAPI   YelpAPI           yelpAPI delegate   self         yelpAPI getData             func getYelpData   - gt  AnyObject           println  getYelpData called           return NSData             func processYelpData data  NSData  - gt  NSData           println  processYelpData called           return NSData            var controller   Controller

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Delegates are a design pattern that allows one object to send messages to another object when a specific event happens  Imagine an object A calls an object B to perform an action  Once the action is complete  object A should know that B has completed the task and take necessary action  this can be achieved with the help of delegates  Here is a tutorial implementing delegates step by step in swift 3  Tutorial Link

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The solutions above seemed a little coupled and at the same time avoid reuse the same protocol in other controllers  that s why I ve come with the solution that is more strong typed using generic type-erasure    noreturn public func notImplemented        fatalError  not implemented yet       public protocol DataChangedProtocol  class      typealias DataType      func onChange t DataType     class AbstractDataChangedWrapper lt DataType gt    DataChangedProtocol       func onChange t  DataType            notImplemented             class AnyDataChangedWrapper lt T  DataChangedProtocol gt    AbstractDataChangedWrapper lt T DataType gt        var base  T      init   base  T            self base   base            override func onChange t  T DataType            base onChange t            class AnyDataChangedProtocol lt DataType gt    DataChangedProtocol       var base  AbstractDataChangedWrapper lt DataType gt       init lt S  DataChangedProtocol where S DataType    DataType gt    s  S           self base   AnyDataChangedWrapper s             func onChange t  DataType            base onChange t             class Source   DataChangedProtocol       func onChange data  String            print   got new value   data               class Target       var delegate  AnyDataChangedProtocol lt String gt        func reportChange data String            delegate  onChange data            var source   Source   var target   Target    target delegate   AnyDataChangedProtocol source  target reportChange  newValue         output  got new value newValue

User · Answer

It is not that different from obj-c  First  you have to specify the protocol in your class declaration  like following   class MyClass  NSUserNotificationCenterDelegate   The implementation will look like following      NSUserNotificationCenterDelegate implementation func userNotificationCenter center  NSUserNotificationCenter  didDeliverNotification notification  NSUserNotification          implementation    func userNotificationCenter center  NSUserNotificationCenter  didActivateNotification notification  NSUserNotification          implementation    func userNotificationCenter center  NSUserNotificationCenter  shouldPresentNotification notification  NSUserNotification  - gt  Bool         implementation     return true     Of course  you have to set the delegate  For example   NSUserNotificationCenter defaultUserNotificationCenter   delegate   self

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First class   protocol NetworkServiceDelegate  class        func didCompleteRequest result  String      class NetworkService  NSObject        weak var delegate  NetworkServiceDelegate       func fetchDataFromURL url   String            delegate  didCompleteRequest url            Second class    class ViewController  UIViewController  NetworkServiceDelegate        let network   NetworkService        override func viewDidLoad             super viewDidLoad           network delegate   self         network fetchDataFromURL  Success                 func didCompleteRequest result  String            print result

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Here s a little help on delegates between two view controllers    Step 1  Make a protocol in the UIViewController that you will be removing will be sending the data   protocol FooTwoViewControllerDelegate class       func myVCDidFinish   controller  FooTwoViewController  text  String      Step2   Declare the delegate in the sending class  i e  UIViewcontroller   class FooTwoViewController  UIViewController       weak var delegate  FooTwoViewControllerDelegate       snip         Step3   Use the delegate in a class method to send the data to the receiving method  which is any method that adopts the protocol    IBAction func saveColor   sender  UIBarButtonItem            delegate  myVCDidFinish self  text  colorLabel text    assuming the delegate is assigned otherwise error     Step 4  Adopt the protocol in the receiving class  class ViewController  UIViewController  FooTwoViewControllerDelegate     Step 5  Implement the delegate method  func myVCDidFinish   controller  FooTwoViewController  text  String        colorLabel text    The Color is      text     controller navigationController popViewController animated  true      Step 6  Set the delegate in the prepareForSegue   override func prepare for segue  UIStoryboardSegue  sender  Any         if segue identifier     mySegue            let vc   segue destination as  FooTwoViewController         vc colorString   colorLabel text         vc delegate   self           And that should work  This is of course just code fragments  but should give you the idea  For a long explanation of this code you can go over to my blog entry here    segues and delegates    If you are interested in what s going on under the hood with a delegate I did write on that here    under the hood with delegates

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Very easy step by step  100  working and tested   step1  Create method on first view controller    func updateProcessStatus isCompleted   Bool       if isCompleted          self labelStatus text    Process is completed       else          self labelStatus text    Process is in progress            step2  Set delegate while push to second view controller   IBAction func buttonAction   sender  Any         let secondViewController   self storyboard  instantiateViewController withIdentifier   secondViewController   as  secondViewController     secondViewController delegate   self     self navigationController  pushViewController secondViewController  animated  true      step3  set delegate like  class ViewController  UIViewController ProcessStatusDelegate    step4  Create protocol  protocol ProcessStatusDelegate NSObjectProtocol  func updateProcessStatus isCompleted   Bool      step5  take a variable  var delegate ProcessStatusDelegate    step6  While go back to previous view controller call delegate method so first view controller notify with data   IBAction func buttonActionBack   sender  Any        delegate  updateProcessStatus isCompleted  true      self navigationController  popViewController animated  true      IBAction func buttonProgress   sender  Any        delegate  updateProcessStatus isCompleted  false      self navigationController  popViewController animated  true

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In swift 4 0  Create a delegate on class that need to send some data or provide some functionality to other classes  Like  protocol GetGameStatus       var score  score   get       func getPlayerDetails       After that in the class that going to confirm to this delegate  class SnakesAndLadders  GetGameStatus       func getPlayerDetails

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I got few corrections to post of  MakeAppPie  First at all when you are creating delegate protocol it should conform to Class protocol  Like in example below   protocol ProtocolDelegate  class       func myMethod controller ViewController  text String      Second  your delegate should be weak to avoid retain cycle   class ViewController  UIViewController       weak var delegate  ProtocolDelegate      Last  you re safe because your protocol is an optional value  That means its  nil  message will be not send to this property  It s similar to conditional statement with respondToselector in objC but here you have everything in one line    if   self delegate respondsToSelector  selector myMethod text            self delegate myMethod self text   you Text        Above you have an obj-C example and below you have Swift example of how it looks   delegate  myMethod self  text  your Text

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Delegates always confused me until I realized that a delegate is just a class that does some work for another class  It s like having someone else there to do all the dirty work for you that you don t want to do yourself  I wrote a little story to illustrate this  Read it in a Playground if you like  Once upon a time       MARK  Background to the story     A protocol is like a list of rules that need to be followed  protocol OlderSiblingDelegate  class          The following command  ie  method  must be obeyed by any         underling  ie  delegate  of the older sibling      func getYourNiceOlderSiblingAGlassOfWater         MARK  Characters in the story  class BossyBigBrother               I can make whichever little sibling is around at         the time be my delegate  ie  slave      weak var delegate  OlderSiblingDelegate           func tellSomebodyToGetMeSomeWater                The delegate is optional because even though             I m thirsty  there might not be anyone nearby             that I can boss around          delegate  getYourNiceOlderSiblingAGlassOfWater               Poor little sisters have to follow  or at least acknowledge      their older sibling s rules  ie  protocol  class PoorLittleSister  OlderSiblingDelegate        func getYourNiceOlderSiblingAGlassOfWater                Little sis follows the letter of the law  ie  protocol              but no one said exactly how she had to respond          print  quot Go get it yourself  quot               MARK  The Story     Big bro is laying on the couch watching basketball on TV  let bigBro   BossyBigBrother       He has a little sister named Sally  let sally   PoorLittleSister       Sally walks into the room  How convenient  Now big bro     has someone there to boss around  bigBro delegate   sally     So he tells her to get him some water  bigBro tellSomebodyToGetMeSomeWater       Unfortunately no one lived happily ever after        The end   In review  there are three key parts to making and using the delegate pattern   the protocol that defines what the worker needs to do the boss class that has a delegate variable  which it uses to tell the worker class what to do the worker class that adopts the protocol and does what is required  Real life In comparison to our Bossy Big Brother story above  delegates are often used for the following practical applications   Communication  one class needs to send some information to another class   Code example 1  sending data from one view controller to another Code example 2  sending text input from a custom keyboard to a text field   Customization  one class wants to allow another class to customize it   The great part is that these classes don t need to know anything about each other beforehand except that the delegate class conforms to the required protocol  I highly recommend reading the following two articles  They helped me understand delegates even better than the documentation did   What is Delegation      A Swift Developer   s Guide How Delegation Works     A Swift Developer   s Guide  One more note Delegates that reference other classes that they do not own should use the weak keyword to avoid strong reference cycles  See this answer for more details

User · Answer

Simple Example   protocol Work  class       func doSomething      class Manager       weak var delegate  Work      func passAlong             delegate  doSomething            class Employee  Work       func doSomething             print  Working on it            let manager   Manager   let developer   Employee   manager delegate   developer manager passAlong      PRINTS  Working on it

[delegates] Delegates in swift?

Examples related to delegates

Examples related to swift

Examples related to delegation