iphone viewWillAppear

viewWillAppear: 
Called when the view is about to made visible. Default does nothing
視圖即將可見時調用。默認情況下不執行任何操作
viewDidAppear: 
Called when the view has been fully transitioned onto the screen. Default does nothing
視圖已完全過渡到屏幕上時調用
viewWillDisappear:
Called when the view is dismissed, covered or otherwise hidden. Default does nothing
視圖被駁回時調用，覆蓋或以其他方式隱藏。默認情況下不執行任何操作
viewDidDisappear:
Called after the view was dismissed, covered or otherwise hidden. Default does nothing
視圖被駁回後調用，覆蓋或以其他方式隱藏。默認情況下不執行任何操作

loadView; 
This is where subclasses should create their custom view hierarchy if they aren't using a nib. Should never be called directly.
這是當他們沒有正在使用nib視圖頁面，子類將會創建自己的自定義視圖層。絕不能直接調用。
viewDidLoad;
Called after the view has been loaded. For view controllers created in code, this is after -loadView. For view controllers unarchived from a nib, this is after the view is set.
在視圖加載後被調用，如果是在代碼中創建的視圖加載器，他將會在loadView方法後被調用，如果是從nib視圖頁面輸出，他將會在視圖設置好後後被調用。