viewDidAppear調用BEFORE它實際上出現了嗎？

Question

我知道這個問題聽起來很像this，但我已經意識到了解決方法。這更多的是一個分析問題。

上面的鏈接是UITabBarController的具體問題，但我也觀察到UINavigationController的行爲，當我，即。沒有動畫。

所以我的問題是爲什麼視圖會在viewDidAppear方法後出現，儘管它的名字暗示了，而且定義說這個視圖已經出現了（定義說視圖已被添加到窗口中）。

我標誌着在方法中設置斷點，看看調用堆棧，這裏是日誌推到UINavigationController：

- (void)viewDidAppear:(BOOL)animated { 
    [super viewDidApear:animated]; 
    NSLog("...");    // <<<<<Breakpoint here 
} 

這裏是日誌：

(gdb) next 
Single stepping until exit from function -[UINavigationController navigationTransitionView:didEndTransition:fromView:toView:], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UINavigationTransitionView _notifyDelegateTransitionDidStopWithContext:], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UINavigationTransitionView _navigationTransitionDidStop], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UIViewAnimationState sendDelegateAnimationDidStop:finished:], which has no line number information. 
(gdb) next 
Single stepping until exit from function +[UIViewAnimationState popAnimationState], which has no line number information. 
(gdb) next 
Single stepping until exit from function dyld_stub_objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function -[NSObject(NSObject) release], which has no line number information. 
(gdb) next 
Single stepping until exit from function dyld_stub_objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UIViewAnimationState dealloc], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UINavigationTransitionView transition:fromView:toView:], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UINavigationTransitionView transition:toView:], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UINavigationController _startDeferredTransitionIfNeeded], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[UILayoutContainerView layoutSubviews], which has no line number information. 
(gdb) next 
Single stepping until exit from function -[CALayer layoutSublayers], which has no line number information. 
(gdb) next 
Single stepping until exit from function dyld_stub_objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function objc_msgSend, which has no line number information. 
(gdb) next 
Single stepping until exit from function -[NSObject(NSObject) release], which has no line number information. 
(gdb) next 
Single stepping until exit from function CALayerLayoutIfNeeded, which has no line number information. 

Answer 1

我發現下面的：

• ViewWillAppear：我使用ViewWillAppear通常只是爲了更新表格上的數據。因此，對於上面的示例，我將使用它實際將我的域中的數據加載到表單中。創建UIViews相當昂貴，你應該儘可能地避免在ViewWillAppear方法上做這件事，因爲當它被調用時，這意味着iPhone已經準備好向用戶展示UIView，並且你在這裏做的任何事情都很重會以非常明顯的方式影響性能（如動畫被延遲等）。

• ViewDidAppear：最後，我使用ViewDidAppear來開始處理需要很長時間才能執行的事情的新線程，例如執行web服務調用以獲取上述表單的額外數據。好處是，因爲視圖已經存在，並顯示給用戶，則可以顯示一個漂亮的「等待」的信息給用戶，而你得到的數據

被盜從SO-問題：What is the difference between -viewWillAppear: and -viewDidAppear:?