blocks|key|3760098|text|据我所知，要做到这一点，唯一可靠的方法是将UINavigationController子类化并覆盖UINavigationBarDelegate+methods|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3760099|–+navigationBar:shouldPushItem:
–+navigationBar:didPushItem:
–+navigationBar:shouldPopItem:
–+navigationBar:didPopItem:|code-block|syntax|javascript|3760100|当然，别忘了给super打电话。|style|CODE|3760101|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/iphone/library/documentation/uikit/reference/UINavigationBarDelegate_Protocol/Reference/Reference.html^0|1D|V|0|0|0|7|5|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|12|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

The only reliable way to do this, as far as I'm aware, is to subclass UINavigationController and override the <a href="http://developer.apple.com/iphone/library/documentation/uikit/reference/UINavigationBarDelegate_Protocol/Reference/Reference.html" rel="nofollow noreferrer">UINavigationBarDelegate methods</a>:

<pre><code>– navigationBar:shouldPushItem:
– navigationBar:didPushItem:
– navigationBar:shouldPopItem:
– navigationBar:didPopItem:
</code></pre>

Don't forget to call <code>super</code>, of course.

blocks|key|3760127|text|简单的方法是向RootViewController添加一个属性，以跟踪它是否已将另一个视图推送到navigationController上。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3760128|-(BOOL)hasPushedSecondView;|code-block|syntax|javascript|3760129|在init方法中初始化为NO。|3760130|在将secondViewControllers视图推送到堆栈之前，请将该属性更新为YES。|3760131|在viewWillAppear中，检查该值并相应地更新视图。根据您希望应用程序如何运行，您可能需要将hasPushedsecondview属性重新设置为NO。|3760132|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Simple approach is to add a property to your RootViewController to track whether or not it has pushed another view onto the navigationController. 

<pre><code>-(BOOL)hasPushedSecondView;
</code></pre>

Initialize to NO in your init method. 

Before pushing secondViewControllers view onto the stack, update the property to YES. 

In viewWillAppear, check the value and update your view accordingly. Depending on how you want the application to behave you may need to reset the hasPushedsecondview property back to NO.

blocks|key|1441053|text|您可以根据应用程序的编写方式来查看leftBarButtonItem或backBarButtonItem，并确定视图的显示方式。如果它在顶部，除非您有一个自定义的leftBarButtonItem，否则那里不会有对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1441054|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

you could take a look at the leftBarButtonItem or backBarButtonItem, based on how your application is written and determine how the view appeared. If it is on top, unless you have a custom leftBarButtonItem, there would be no object there.

blocks|key|694288|text|您可以通过UIViewController子类上的几个方法直接确定这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|694289|来自Apple's+documentation|offset|length|694290|694291|有时，了解视图出现或消失的原因是很有用的。例如，您可能想知道视图是因为刚添加到容器中而出现，还是因为其他遮蔽它的内容被删除而出现。在使用导航控制器时，这个特定的示例经常出现；您的内容控制器的视图可能是因为视图控制器刚被压入导航堆栈，也可能是因为它之前的控制器是从堆栈中弹出的。|blockquote|694292|694293|UIViewController类提供了视图控制器可以调用的方法，以确定发生外观更改的原因。|694294|694295|694296|isMovingFromParentViewController:视图被隐藏，因为视图控制器已从container|unordered-list-item|694297|isMovingToParentViewController:中删除。显示视图是因为它正被添加到container|694298|isBeingPresented：视图中。正在显示它，因为它是由另一个视图呈现的。controller|style|BOLD|694299|isBeingDismissed：视图正在隐藏，因为它刚刚丢失了|694300|694301|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/RespondingtoDisplay-Notifications/RespondingtoDisplay-Notifications.html#//apple_ref/doc/uid/TP40007457-CH12-SW7^0|0|2|L|0|0|0|0|0|0|0|0|0|0|0|G|0|0|G|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@$D|1A|E|1B|1|1C]]|A|$]]|$1|F|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|1E|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1G|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1J|8|@]|9|@]|A|$]]|$1|R|3|S|5|Q|7|1K|8|@]|9|@]|A|$]]|$1|T|3|U|5|Q|7|1L|8|@$D|1M|E|1N|V|W]]|9|@]|A|$]]|$1|X|3|Y|5|Q|7|1O|8|@$D|1P|E|1Q|V|W]]|9|@]|A|$]]|$1|Z|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]]|11|$12|$5|13|14|15|A|$16|17]]]]

You can determine this directly via a couple of methods on your UIViewController subclass.

From <a href="https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/RespondingtoDisplay-Notifications/RespondingtoDisplay-Notifications.html#//apple_ref/doc/uid/TP40007457-CH12-SW7" rel="nofollow">Apple's documentation</a>:

<blockquote>
 Occasionally, it can be useful to know why a view is appearing or
 disappearing. For example, you might want to know whether a view
 appeared because it was just added to a container or whether it
 appeared because some other content that obscured it was removed. This
 particular example often appears when using navigation controllers;
 your content controller’s view may appear because the view controller
 was just pushed onto the navigation stack or it might appear because
 controllers previously above it were popped from the stack.
 
 The UIViewController class provides methods your view controller can
 call to determine why the appearance change occurred.
</blockquote>

<ul>
<li>isMovingFromParentViewController: view was hidden because view controller was removed from container</li>
<li>isMovingToParentViewController: view is shown because it's being added to a container</li>
<li>isBeingPresented: view is being shown because it was presented by another view controller</li>
<li>isBeingDismissed: view is being hidden because it was just dimissed</li>
</ul>

Using a UINavigationViewController, how do I find out how a view has appeared?

The view has either appeared in a straightforward manner, as the first view in the UINavigationController stack. Or it has appeared because a second view has been popped and the first view has revealed itself again. How do you find out which of these happened?

How to tell if view has appeared via popping or not?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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使用UINavigationViewController，我如何知道视图是如何显示的？视图或者以一种直接的方式出现，作为UINavigationController堆栈中的第一个视图。或者，它之所以出现，是因为第二个视图已经弹出，第一个视图再次显露出来。您如何找出其中哪些发生了？

问如何通过弹出来判断视图是否已经出现？
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