1. 实例化 alloc/init, initWithNibName
2.awakeFromNib 从nib创建Controller对象
3.get/set outlets
4. viewDidLoad
5.(几何内容确定时 才进入)viewWill/DidLayoutSubViews
6.viewWill/DidAppear 进入屏幕时
7.(可见内容有变化时 才有)viewWill/DidLayoutSubViews
8.viewWill/DidDisappear 退出屏幕时
9.(内存不足时)didReceivedMemoryWarning