What method is called after tap back button in ios?

Ans : 

When you go back the following methods will be called:

Notifies the view controller that its view is about to be added to a view hierarchy : 

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
}


Notifies the view controller that its view was added to a view hierarchy : 

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

}