Adding a view controller as a subview in another view controller

Question

I have found few posts for this problem but none of them solved my issue   Say like I ve     ViewControllerA ViewControllerB   I tried to add ViewControllerB as a subview in ViewControllerA but  it s throwing an error like  fatal error  unexpectedly found nil while unwrapping an Optional value    Below is the code     ViewControllerA  var testVC  ViewControllerB   ViewControllerB     override func viewDidLoad         super viewDidLoad       self testVC view frame   CGRectMake 0  0  350  450       self view addSubview testVC view          Do any additional setup after loading the view      ViewControllerB is just a simple screen with a label in it   ViewControllerB    IBOutlet weak var test  UILabel   override func viewDidLoad         super viewDidLoad       test text    Success     Throws ERROR here  fatal error  unexpectedly found nil while unwrapping an Optional value      EDIT  With the suggested solution from the user answers  ViewControllerB in ViewControllerA is going off the screen  Grey border is the frame I have created for the subview

User · Answer

func callForMenuView              if  isOpen                 isOpen   true          let menuVC   MenuViewController   self storyboard  instantiateViewController withIdentifier   menu   as  MenuViewController         self view addSubview menuVC view          self addChildViewController menuVC          menuVC view layoutIfNeeded            menuVC view frame CGRect x  0 - UIScreen main bounds size width  y  0  width  UIScreen main bounds size width-90  height  UIScreen main bounds size height            UIView animate withDuration  0 3  animations       - gt  Void in             menuVC view frame CGRect x  0  y  0  width  UIScreen main bounds size width-90  height  UIScreen main bounds size height          completion nil        else if isOpen                isOpen   false       let viewMenuBack   UIView   view subviews last           UIView animate withDuration  0 3  animations       - gt  Void in             var frameMenu   CGRect   viewMenuBack frame             frameMenu origin x   -1   UIScreen main bounds size width             viewMenuBack frame   frameMenu             viewMenuBack layoutIfNeeded               viewMenuBack backgroundColor   UIColor clear            completion     finished  - gt  Void in             viewMenuBack removeFromSuperview

User · Answer

For Add and Remove ViewController  var secondViewController  SecondViewController        Adding   func add ViewController         let controller    self storyboard  instantiateViewController withIdentifier   quot secondViewController quot  as  SecondViewController     controller view frame   self view bounds     self view addSubview controller view      self addChild controller      controller didMove toParent  self      self secondViewController   controller       Removing func remove ViewController secondViewController SecondViewController         if secondViewController    nil           if self view subviews contains secondViewController  view                 secondViewController  view removeFromSuperview

User · Answer

Please also check the official documentation on implementing a custom container view controller   https   developer apple com library content featuredarticles ViewControllerPGforiPhoneOS ImplementingaContainerViewController html   apple ref doc uid TP40007457-CH11-SW1  This documentation has much more detailed information for every instruction and also describes how to do add transitions   Translated to Swift 3   func cycleFromViewController oldVC  UIViewController                 newVC  UIViewController          Prepare the two view controllers for the change     oldVC willMove toParentViewController  nil     addChildViewController newVC         Get the start frame of the new view controller and the end frame       for the old view controller  Both rectangles are offscreen r    newVC view frame   view frame offsetBy dx  view frame width  dy  0     let endFrame   view frame offsetBy dx  -view frame width  dy  0         Queue up the transition animation     self transition from  oldVC  to  newVC  duration  0 25  animations             newVC view frame   oldVC view frame         oldVC view frame   endFrame              Bool  in         oldVC removeFromParentViewController           newVC didMove toParentViewController  self

User · Answer

A couple of observations    When you instantiate the second view controller  you are calling ViewControllerB    If that view controller programmatically creates its view  which is unusual  that would be fine  But the presence of the IBOutlet suggests that this second view controller s scene was defined in Interface Builder  but by calling ViewControllerB    you are not giving the storyboard a chance to instantiate that scene and hook up all the outlets  Thus the implicitly unwrapped UILabel is nil  resulting in your error message   Instead  you want to give your destination view controller a  storyboard id  in Interface Builder and then you can use instantiateViewController withIdentifier   to instantiate it  and hook up all of the IB outlets   In Swift 3   let controller   storyboard  instantiateViewController withIdentifier   scene storyboard id     You can now access this controller s view  But if you really want to do addSubview  i e  you re not transitioning to the next scene   then you are engaging in a practice called  view controller containment   You do not just want to simply addSubview  You want to do some additional container view controller calls  e g    let controller   storyboard  instantiateViewController withIdentifier   scene storyboard id   addChild controller  controller view frame           or  better  turn off  translatesAutoresizingMaskIntoConstraints  and then define constraints for this subview view addSubview controller view  controller didMove toParent  self    For more information about why this addChild  previously called addChildViewController  and didMove toParent    previously called didMove toParentViewController    are necessary  see WWDC 2011 video  102 - Implementing UIViewController Containment  In short  you need to ensure that your view controller hierarchy stays in sync with your view hierarchy  and these calls to addChild and didMove toParent   ensure this is the case   Also see Creating Custom Container View Controllers in the View Controller Programming Guide      By the way  the above illustrates how to do this programmatically  It is actually much easier if you use the  container view  in Interface Builder      Then you don t have to worry about any of these containment-related calls  and Interface Builder will take care of it for you   For Swift 2 implementation  see previous revision of this answer

User · Answer

Thanks to Rob  Updated Swift 4 2 syntax let controller WalletView   self storyboard  instantiateViewController withIdentifier   quot MyView quot   as  WalletView controller view frame   self view bounds self view addSubview controller view  self addChild controller  controller didMove toParent  self

User · Answer

This code will work for Swift 4 2   let controller SecondViewController    self storyboard  instantiateViewController withIdentifier   quot secondViewController quot   as   SecondViewController controller view frame   self view bounds  self view addSubview controller view  self addChild controller  controller didMove toParent  self

User · Answer

Thanks to Rob  Adding detailed syntax for your second observation   let controller MyView   self storyboard  instantiateViewControllerWithIdentifier  quot MyView quot   as  MyView controller ANYPROPERTY THEVALUE    If you want to pass value controller view frame   self view bounds self view addSubview controller view  self addChildViewController controller  controller didMoveToParentViewController self   And to remove the viewcontroller   self willMoveToParentViewController nil  self view removeFromSuperview   self removeFromParentViewController

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