1.viewDidLoad 里調(diào)用presentViewController(presentModalViewController)無效果的問題

場景：在viewDidLoad里面調(diào)用了presentViewController 發(fā)現(xiàn)沒有預(yù)期效果，最終放棄在該方法里面操作視圖控制器（用push 可以有預(yù)期的效果，why ?）,放在了viewWillAppear里面去present

參考：When viewDidLoad is called, there is no guarantee that the view controller hierarchy is loaded in the navigation tree. Moving the logic to a later stage (for example: viewWillAppear) should resolve that issue as presentingController should be loaded by then.