blocks|key|584529|text|您可以从AppDelegate发送一个ViewController并在您的ViewController中订阅它，而不是试图跟踪哪个NSNotification是最新的。这样，视图控制器就可以跟踪它是否需要调用viewDidAppear。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|584530|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|$]]

Rather than trying to keep track of which ViewController is current, you could send a NSNotification from your AppDelegate and subscribe to it in your ViewController.. That way the view controller keeps track of whether or not it needs to call viewDidAppear.

blocks|key|584566|text|我建议使用通知。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|584567|在你的应用程序代理的applicationdidBecomeActive方法中，放入以下代码：|584568|[[NSNotificationCenter+defaultCenter]+postNotificationName:@"appDidBecomeActive"+object:nil];|code-block|syntax|javascript|584569|在当前活动的视图控制器的init方法中，订阅通知。|584570|[[NSNotificationCenter+defaultCenter]+addObserver:self+
+++++++++++++++++++++++++++++++++++++++++selector:@selector(updateStuff)++++++++
+++++++++++++++++++++++++++++++++++++++++++++name:@"appDidBecomeActive"+
+++++++++++++++++++++++++++++++++++++++++++object:nil];|584571|在你的控制器中实现"updateStuff“方法，当应用程序激活时，你应该能够做任何你想做的事情。|584572|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I would recommend using notifications.

In your app delegate's applicationdidBecomeActive method put in this code:

<pre><code>[[NSNotificationCenter defaultCenter] postNotificationName:@"appDidBecomeActive" object:nil];
</code></pre>

In your current active view controller's init method subscribe to the notification.

<pre><code>[[NSNotificationCenter defaultCenter] addObserver:self 
 selector:@selector(updateStuff) 
 name:@"appDidBecomeActive" 
 object:nil];
</code></pre>

Implement the "updateStuff" method in your controller and you should be able to do whatever you want when the app becomes active.

blocks|key|584623|text|您的窗口将具有AppDelegate属性，该窗口将具有rootViewController属性。你可以在这里找到你的viewController。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|584624|如果您使用的是TabBarController，根视图控制器将是选项卡栏控制器，您可以调用选项卡栏控制器的selectedViewController来获取当前的viewController。|584625|UIViewController+*rootViewController+=+[[[[UIApplication+sharedApplication]+delegate]+window]+rootViewController];
if+([rootViewController+isKindOfClass:[UITabBarController+Class]])
++++rootViewController+=+((UITabBarController+*)rootViewController).selectedViewController;
else+if+([rootViewController+isKindOfClass:[UINavigationController+Class]])
++++rootViewController+=+((UINavigationController+*)rootViewController).topViewController;

[rootViewController+viewDidAppear];|code-block|syntax|javascript|584626|如果您有一个带有导航控制器或模式视图的更复杂的视图层次结构，则可以调用presentedViewController或topViewController。|584627|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

your AppDelegate will have a window property, that window will have a rootViewController property. You can find your viewController here.

If you are using a TabBarController, the rootviewcontroller will be the tabbarcontroller, and you can call the tabbarcontroller's selectedViewController to get the current viewController.

<pre><code>UIViewController *rootViewController = [[[[UIApplication sharedApplication] delegate] window] rootViewController];
if ([rootViewController isKindOfClass:[UITabBarController Class]])
 rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
else if ([rootViewController isKindOfClass:[UINavigationController Class]])
 rootViewController = ((UINavigationController *)rootViewController).topViewController;

[rootViewController viewDidAppear];
</code></pre>

If you have a more complex view hierarchy with navigation controllers, or modal views, you can call on presentedViewController, or topViewController.

blocks|key|368953|text|操作系统不是从应用代理发送通知，而是自动发送通知，您可以观察到：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|368954|[[NSNotificationCenter+defaultCenter]+addObserver:self
++++++++++++++++++++++++++++++++++++++selector:@selector(initSongInfo)
++++++++++++++++++++++++++++++++++++++name:UIApplicationDidBecomeActiveNotification
++++++++++++++++++++++++++++++++++++++object:nil];|code-block|syntax|javascript|368955|当然，确保在dealloc方法之前或内部的某个时间停止观察，方法是调用：|368956|[[NSNotificationCenter+defaultCenter]+removeObserver:self+
++++++++++++++++++++++++++++++++++++++name:UIApplicationDidBecomeActiveNotification+
++++++++++++++++++++++++++++++++++++++object:nil];|368957|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Instead of sending a notification from your app delegate, the OS sends a notification automatically that you can observe:
<pre><code>[[NSNotificationCenter defaultCenter] addObserver:self
 selector:@selector(initSongInfo)
 name:UIApplicationDidBecomeActiveNotification
 object:nil];
</code></pre>
and of course make sure to stop observing sometime before or inside your dealloc method, by calling:
<pre><code>[[NSNotificationCenter defaultCenter] removeObserver:self 
 name:UIApplicationDidBecomeActiveNotification 
 object:nil];
</code></pre>

I feel I am missing a trick here...

I just want to call viewDidLoad or viewDidAppear on the current active view controller when applicationDidBecomeActive gets called, so I can reset some animations or whatever, when the app is started up again from the background. Some of my views don't care, but others really need to know.

I am using Storyboards and my app delegate file has the standard functions - but all with EMPTY bodies. For example, didFinishLaunchingWithOptions just returns YES and does nothing else. Storyboard automagically does everything I guess.

So how can I talk to the current view controller from my rather blank, information free, app delegate?

How to tell the active view controller when applicationDidBecomeActive is called?

我觉得我错过了一个小把戏...我只想在applicationDidBecomeActive被调用时调用当前活动视图控制器上的viewDidLoad或viewDidAppear，这样当应用程序从后台再次启动时，我就可以重置一些动画或其他东西。我的一些观点并不关心，但其他人确实需要知道。我使用的是故事板，我的应用委托文件有...

问当applicationDidBecomeActive被调用时，如何告诉活动视图控制器？
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问当applicationDidBecomeActive被调用时，如何告诉活动视图控制器？
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