43

我打算在我的应用程序中实现多任务。我可以在这里看到很多方法来做到这一点，AppDelegate比如applicationWillResignActive, applicationDidEnterBackground, applicationWillEnterForeground, ...

但是....我没有看到它们应该被使用的方式，也没有看到它们为什么不在 ViewControllers 中......也没有看到它们在这里的用途。

我的意思是：当应用程序进入后台时，我不知道我的用户在哪个视图上。反过来，当应用程序进入前台时，我怎么知道该做什么以及我可以调用什么来更新视图？

如果这些方法在每个视图控制器中，我会理解的，但是在这里，我看不出它们可以具体用于什么......

您能帮我理解将事物实施到这些方法中的方式吗？

4

2 回答 2

132

UIApplicationDidEnterBackgroundNotification当应用程序进入后台时，每个对象都会收到通知。因此，要在应用程序进入后台时运行一些代码，您只需在您想要的地方收听该通知：

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(appHasGoneInBackground:)
                                             name:UIApplicationDidEnterBackgroundNotification
                                           object:nil];

当您不再需要收听它时，不要忘记释放监听器：

[[NSNotificationCenter defaultCenter] removeObserver:self];

最好的，您可以使用以下通知以相同的方式播放：

  • UIApplicationDidEnterBackgroundNotification
  • UIApplicationWillEnterForegroundNotification
  • UIApplicationWillResignActiveNotification
  • UIApplicationDidBecomeActiveNotification
于 2011-09-07T22:04:08.643 回答
8

它们不在您的任何视图控制器中，因为 iOS 采用“委托”设计模式，您可以确保方法会在需要时触发类（在本例中为您的应用程序的 App Delegate）。

作为一个学习过程，你为什么不把 NSLog 放在那些方法中，看看它们什么时候被解雇？

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{    

    // Override point for customization after application launch.
    NSLog(@"didFinishLaunchingWithOptions");
    [self.window makeKeyAndVisible];

    return YES;
}


- (void)applicationWillResignActive:(UIApplication *)application 
{
    /*
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
     */
    NSLog(@"applicationWillResignActive");
}


- (void)applicationDidEnterBackground:(UIApplication *)application 
{
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     If your application supports background execution, called instead of applicationWillTerminate: when the user quits.
     */
    NSLog(@"applicationDidEnterBackground");
}


- (void)applicationWillEnterForeground:(UIApplication *)application 
{
    /*
     Called as part of  transition from the background to the active state: here you can undo many of the changes made on entering the background.
     */
    NSLog(@"applicationWillEnterForeground");
}


- (void)applicationDidBecomeActive:(UIApplication *)application 
{
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     */
    NSLog(@"applicationDidBecomeActive");
}


- (void)applicationWillTerminate:(UIApplication *)application 
{
    /*
     Called when the application is about to terminate.
     See also applicationDidEnterBackground:.
     */
    NSLog(@"applicationWillTerminate");
}
于 2011-01-31T03:37:10.647 回答