uiviewcontroller_lifecycle

平時在講ViewController的生命周期時，我們只大多只關(guān)注以下六個方法：

• viewDidLoad
  *viewWillAppear
• viewDidAppear
• viewWillDisappear
• viewDidDisappear
• viewDidUnload

其實ViewController的生命周期如下：

• loadView^[1]
• viewDidLoad^[1]
• viewWillAppear
• viewWillLayoutSubviews ^[2]

  Called to notify the view controller that its view is about to layout its subviews.

• viewDidLayoutSubviews^[2]

Called to notify the view controller that its view has just laid out its subviews.

• viewDidAppear
• viewWillLayoutSubviews
• viewDidLayoutSubviews
• viewWillDisappear
• viewDidDisappear
• viewDidUnload

1. If you manually nil out your view during didReceiveMemoryWarning, loadView and viewDidLoad will be called again. That is, by default loadView and viewDidLoad only gets called once per view controller instance. ? ?

2. May be called an additional 0 or more times .viewWillLayoutSubviews and viewDidLayoutSubviews will also be called at other times when subviews of the main view are loaded, for example when cells of a table view or collection view are loaded. ? ?