blocks|key|667748|text|在您的应用程序代理上使用-+(void)applicationWillResignActive:(UIApplication+*)application。您还可以在其他对象上注册UIApplicationWillResignActiveNotification通知。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|667749|不过，您不一定需要暂停计时器。如果你什么都不做，应用程序无论如何都会进入睡眠状态，并且不会执行任何代码。当你再次激活时，你的计时器可能会触发(如果你激活了)。如果你需要做一些特殊的事情，你也可以注册“变成活动的”委托方法和通知。|667750|entityMap^0|C|1S|2H|15|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

<code>- (void)applicationWillResignActive:(UIApplication *)application</code> on your app delegate. You can also register for the <code>UIApplicationWillResignActiveNotification</code> notification on other objects.

You don't necessarily need to pause the timer, though. If you don't do anything, the app will get put to sleep anyway and won't execute any code. Presumably your timer will fire when you become active again (if you do). If you need to do something special there are 'did become active' delegate methods and notifications you can register for as well.

blocks|key|667795|text|在您的应用程序AppDelegate上，iOS将调用(void)applicationDidEnterBackground:(UIApplication+*)application方法。你可以把你的定时器停在那里。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|667796|entityMap^0|Q|1S|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

On your applications AppDelegate the <code>(void)applicationDidEnterBackground:(UIApplication *)application</code> method will be called by iOS. You can stop your timer in there.

blocks|key|453587|text|您可以让任何对应用程序何时进入后台接收通知感兴趣的类。这是将这些类与AppDelegate耦合的一个很好的替代方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|453588|在初始化所述类时：|453589|[[NSNotificationCenter+defaultCenter]+addObserver:self+selector:@selector(appWillResignActive:)+name:UIApplicationWillResignActiveNotification+object:nil];
[[NSNotificationCenter+defaultCenter]+addObserver:self+selector:@selector(appWillTerminate:)+name:UIApplicationWillTerminateNotification+object:nil];|code-block|syntax|javascript|453590|响应通知|453591|-(void)appWillResignActive:(NSNotification*)note
{

}
-(void)appWillTerminate:(NSNotification*)note
{
++++[[NSNotificationCenter+defaultCenter]+removeObserver:self+name:UIApplicationWillResignActiveNotification+object:nil];
++++[[NSNotificationCenter+defaultCenter]+removeObserver:self+name:UIApplicationWillTerminateNotification+object:nil];

}|453592|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can have any class interested in when the app goes into the background receive notifications. This is a good alternative to coupling these classes with the AppDelegate.

When initializing said classes:

<pre><code>[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillResignActive:) name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillTerminate:) name:UIApplicationWillTerminateNotification object:nil];
</code></pre>

Responding to the notifications

<pre><code>-(void)appWillResignActive:(NSNotification*)note
{

}
-(void)appWillTerminate:(NSNotification*)note
{
 [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillResignActiveNotification object:nil];
 [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillTerminateNotification object:nil];

}
</code></pre>

blocks|key|453649|text|对于那些希望在Swift中做到这一点的人：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|453650|在init上|offset|length|style|CODE|453651|NSNotificationCenter.defaultCenter().addObserver(self,+selector:+#selector(applicationWillResignActive),+name:+UIApplicationWillResignActiveNotification,+object:+nil)|code-block|syntax|javascript|453652|在deinit上|453653|NSNotificationCenter.defaultCenter().removeObserver(self,+name:+UIApplicationWillResignActiveNotification,+object:+nil)|453654|响应通知：|453655|dynamic+private+func+applicationWillResignActive()+{
++++//+Do+things+here
}|453656|Apple鼓励我们在Swift中尽可能避免动态分派和Objective-C选择器，但这仍然是最方便的方法。|453657|entityMap^0|0|1|4|0|0|1|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@$D|10|E|11|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|12|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|16|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|17|8|@]|9|@]|A|$]]|$1|S|3|T|5|J|7|18|8|@]|9|@]|A|$K|L]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|X|$]]

For those looking to do this in Swift:

On <code>init</code>:

<pre><code>NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(applicationWillResignActive), name: UIApplicationWillResignActiveNotification, object: nil)
</code></pre>

On <code>deinit</code>:

<pre><code>NSNotificationCenter.defaultCenter().removeObserver(self, name: UIApplicationWillResignActiveNotification, object: nil)
</code></pre>

Responding to the notification:

<pre><code>dynamic private func applicationWillResignActive() {
 // Do things here
}
</code></pre>

Apple encourages us to avoid dynamic dispatch and Objective-C selectors whenever possible in Swift, but this is still the most convenient way to do this.

blocks|key|667941|text|只有一个附注:如果您注册了一个要通知后台的控制器A，请注意它将被调用，即使您(例如..)按下第二个控制器B，您将显示B:如果此行为不正确，最好在|type|unstyled|depth|inlineStyleRanges|entityRanges|data|667942|didAppear外观/威利消失。|667943|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

only a side note:
If you register a controller A to be notified going background, be careful that it will be called even if you (for example..) push a second controller B and You are displaying B: 
If this behaviour is not correct, is better to register/unregister in 

didAppear/WillDisappear.

blocks|key|667960|text|Swift+4：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|667961|init()+{
++++NotificationCenter.default.addObserver(self,
+++++++++++++++++++++++++++++++++++++++++++selector:+#selector(applicationWillResignActive),
+++++++++++++++++++++++++++++++++++++++++++name:+NSNotification.Name.UIApplicationWillResignActive,
+++++++++++++++++++++++++++++++++++++++++++object:+nil)
}

deinit+{
++++NotificationCenter.default.removeObserver(self,
++++++++++++++++++++++++++++++++++++++++++++++name:+NSNotification.Name.UIApplicationWillResignActive,
++++++++++++++++++++++++++++++++++++++++++++++object:+nil)
}

@objc+private+func+applicationWillResignActive()+{
++++self.header.blur.effect+=+nil
}|code-block|syntax|javascript|667962|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Swift 4: 

<pre><code>init() {
 NotificationCenter.default.addObserver(self,
 selector: #selector(applicationWillResignActive),
 name: NSNotification.Name.UIApplicationWillResignActive,
 object: nil)
}

deinit {
 NotificationCenter.default.removeObserver(self,
 name: NSNotification.Name.UIApplicationWillResignActive,
 object: nil)
}

@objc private func applicationWillResignActive() {
 self.header.blur.effect = nil
}
</code></pre>

blocks|key|453735|text|在swift+4.1中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|453736|我使用闭包版本：|453737|var+observer:+NSObjectProtocol!

//+inside+init+or+viewDidLoad:
observer+=+NotificationCenter.default.addObserver(forName:+.UIApplicationWillResignActive,+object:+nil,+queue:+nil)+{+_+in
++++print("willResignActive")
}

deinit+{
++++NotificationCenter.default.removeObserver(observer)
}|code-block|syntax|javascript|453738|addObserver方法返回一个不透明的对象，该对象需要在某个时刻被移除。|offset|length|style|CODE|453739|entityMap^0|0|0|0|0|B|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]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

In swift 4.1:

I use the closure version:

<pre><code>var observer: NSObjectProtocol!

// inside init or viewDidLoad:
observer = NotificationCenter.default.addObserver(forName: .UIApplicationWillResignActive, object: nil, queue: nil) { _ in
 print("willResignActive")
}

deinit {
 NotificationCenter.default.removeObserver(observer)
}
</code></pre>

The <code>addObserver</code> method returns an opaque object that needs to be removed at some point.

blocks|key|453792|text|这是一个使用闭包的更好的解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|453793|声明观察者|453794|var+backgroundObserver:+NSObjectProtocol?|code-block|syntax|javascript|453795|在viewDidLoad中初始化观察者|453796|backgroundObserver+=+NotificationCenter.default.addObserver(forName:+UIApplication.willResignActiveNotification,+object:+nil,+queue:+.main)+{+[weak+self]+notification+in
++//+Do+what+you+want+to+do+when+app+would+go+to+background/+resign+active++
}|453797|不要忘记删除deinit中的观察者|453798|deinit+{
++++if+let+observer+=+backgroundObserver+{
++++++++NotificationCenter.default.removeObserver(observer)
++++}+
}|453799|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

This is a better solution using closure
Declare observer
<pre><code>var backgroundObserver: NSObjectProtocol?
</code></pre>
Initialize observer in viewDidLoad
<pre><code>backgroundObserver = NotificationCenter.default.addObserver(forName: UIApplication.willResignActiveNotification, object: nil, queue: .main) { [weak self] notification in
 // Do what you want to do when app would go to background/ resign active 
}
</code></pre>
Don't forget to remove observer in deinit
<pre><code>deinit {
 if let observer = backgroundObserver {
 NotificationCenter.default.removeObserver(observer)
 } 
}
</code></pre>

blocks|key|668059|text|在Swift+5.1中|type|unstyled|depth|inlineStyleRanges|entityRanges|data|668060|++++override+func+viewWillAppear(_+animated:+Bool)+{
+++++++++super.viewWillAppear(animated)

+++++++++NotificationCenter.default.addObserver(self,+selector:+#selector(applicationWillResignActive),+name:+UIApplication.willResignActiveNotification,+object:+nil)
++++
+++++++++NotificationCenter.default.addObserver(self,+selector:+#selector(applicationDidBecomeActive),+name:+UIApplication.didBecomeActiveNotification,+object:+nil)
++++++++}
++++
++++override+func+viewWillDisappear(_+animated:+Bool)+{+
++++++++super.viewWillDisappear(animated)

++++++++NotificationCenter.default.removeObserver(self,+name:+UIApplication.willResignActiveNotification,+object:+nil)

++++++++NotificationCenter.default.removeObserver(self,+name:+UIApplication.didBecomeActiveNotification,+object:+nil)
++++}


@objc+private+func+applicationWillResignActive()+{
++++}

++++@objc+private+func+applicationDidBecomeActive()+{
++++}|code-block|syntax|javascript|668061|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

In Swift 5.1
<pre><code> override func viewWillAppear(_ animated: Bool) {
 super.viewWillAppear(animated)

 NotificationCenter.default.addObserver(self, selector: #selector(applicationWillResignActive), name: UIApplication.willResignActiveNotification, object: nil)
 
 NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
 }
 
 override func viewWillDisappear(_ animated: Bool) { 
 super.viewWillDisappear(animated)

 NotificationCenter.default.removeObserver(self, name: UIApplication.willResignActiveNotification, object: nil)

 NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
 }


@objc private func applicationWillResignActive() {
 }

 @objc private func applicationDidBecomeActive() {
 }
</code></pre>

I have a view controller that uses an <code>NSTimer</code> to execute some code.

What's the best way to detect when the app is going to the background so I can pause the timer?

What's the best way to detect when the app is entering the background for my view?

Objective-C

Swift

我有一个视图控制器，它使用NSTimer来执行一些代码。检测应用程序何时转到后台的最佳方法是什么，以便我可以暂停计时器？

问检测应用程序何时进入我视图的背景的最佳方法是什么？
EN

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