在实际出现之前调用过viewDidAppear吗？

问题描述

| 我知道这个问题听起来与此类似，但是我已经知道解决方法。这更多是一个分析问题。 上面的链接是特定于

UITabBarController

的问题，但是当我I2ѭ时，我也观察到

UINavigationController

的行为。没有动画。 所以我的问题是，为什么视图在

viewDidAppear

方法之后出现，但其名称暗示并定义说该视图已经出现（定义说视图已添加到窗口中）。 我已经在方法中标记了一个断点以查看调用堆栈，这是推送到

UINavigationController

的日志：

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

这是日志：

(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 -[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 CALayerLayoutIfNeeded,which has no line number information.

    

解决方法

        我发现以下内容： ViewWillAppear：我通常使用ViewWillAppear只是为了更新表单上的数据。因此，对于上面的示例，我将使用它来将域中的数据实际加载到表单中。创建UIView相当昂贵，您应该避免在ViewWillAppear方法上执行尽可能多的操作，因为调用该方法时，它意味着iPhone已经准备好向用户显示UIView，而您在此处所做的任何繁重的工作将以非常明显的方式影响性能（例如动画被延迟等）。 ViewDidAppear：最后，我使用ViewDidAppear为需要很长时间才能执行的事情启动新线程，例如进行webservice调用以获取上述表单的额外数据，这是因为视图已经存在并且正在向用户显示，您可以在获取数据的同时向用户显示一个很好的“正在等待”消息 从SO问题中窃取：-viewWillAppear：和-viewDidAppear：有什么区别？