UIViewController 生命周期

- (void)loadView{}
// viewController 会在view的property被请求并且当前view值为nil时调用。如果是手动创建view，你应该重载这个函数，切记不要在重载的时候调用[super loadView]

- (void)viewDidLoad {}
// 进一步初始化你的views。负责view及其子view被加载进内存之后的数据初始化

- (void)viewWillAppear:(BOOL)animated{}

- (void)viewWillLayoutSubviews{}

- (void)viewDidLayoutSubviews{}

- (void)viewDidAppear:(BOOL)animated{}

- (void)viewWillDisappear:(BOOL)animated{}

- (void)viewDidDisappear:(BOOL)animated{}

- (void)dealloc{}