iOS开发--控制器的生命周期

[ViewController viewDidLoad]->[ViewController viewWillAppear]->[ViewController viewDidAppear]->[ViewController viewWillDisappear]->[ViewController viewDidDisappear]

viewDidLoad 只调用一次（加载子控件/网络加载数据）

viewWillAppear、viewDidAppear、viewWillDisappear、viewDidDisappear 每次进入都会调用