Explain why this method is needed?

Question

Objective-C

When I add childController as a child controller, why do I need to execute the didMoveToParentViewController:self method at the end? Here is part of the code

[self addChildViewController: childController];
[self.view insertSubview: childController.view atIndex:0];
[childController didMoveToParentViewController:self];

Answer 1

This method signals to the child ViewController that its "transition" to the parent container is complete.
This way you can react to the end of adding your controller to the hierarchy. Now, it seems like this method does nothing for the base UIViewController. However, YOU MUST call it when implementing your custom container. Firstly, no one guarantees that in ios> 9 he will not start doing something. Secondly, there are a lot of third-party libraries / pods where these methods can be overridden in custom components. And now, if you shove them into your custom container and do not call didMoveToParentViewController, then there will be undefined behavior