View生命週期之viewWill/DidAppear()， viewWill/DidDissappear() &解決問題Fatal error: Unexpectedly found nil

發生順序：viewDidLoad() -> viewWillAppear() -> viewDidAppear() -> viewWillDissappear() -> viewDidDisappear() 有ViewController1和ViewController2.兩個關係如下，點擊click, view1 -> view2, 點擊back, view2 -> view1 view1代碼如

>>阅读原文<<