Where should I be setting autolayout constraints when creating views programmatically

Question

I see different examples where constraints are set. Some set them in viewDidLoad / loadView (after the subview was added). Others set them in the m

Answer 1

I have this solution to change constraints before those who are in the storyboard are loaded. This solution removes any lags after the view is loaded.

-(void)updateViewConstraints{

    dispatch_async(dispatch_get_main_queue(), ^{

            //Modify here your Constraint -> Activate the new constraint and deactivate the old one

            self.yourContraintA.active = true;
            self.yourContraintB.active= false;
            //ecc..
           });

    [super updateViewConstraints]; // This must be the last thing that you do here -> if! ->Crash!
}

Answer 2

Following example is to pass any view to another class. create my view from storyboard

Swift 5.0

    override func viewWillAppear(_ animated: Bool) {
        
      super.viewWillAppear(animated) 
        DispatchQueue.main.async {
            self.abcInstance = ABC(frame: self.myView.frame)
          } 
      }

 

If you miss DispatchQueue.main.async , it will take time to update constraints in viewWillAppear. Create myView in storyboard and give constraints same as screen width & height , then try printing frame of myView. it will give accurate value in DispatchQueue.main.async or in viewDidAppear but not give accurate value in viewWillAppear without DispatchQueue.main.async.