A viewcontroller push b viewController
B loadView()
B viewDidLoad()
A viewWillDisappear
B viewWillAppear
B viewWillLayoutSubviews()
B viewDidLayoutSubviews()
A viewDidDisappear
B viewDidAppear
B vc back to A vc
B viewWillDisappear
A viewWillAppear
B viewDidDisappear
A viewDidAppear
從來沒認真過這個順序，考過之後，才發現跟認知有點距離。我應該也背不下來。XD
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