在AppDelegate中使用background/foreground方法

Question

我打算在我的应用程序中实现多任务.我在这里可以看到很多的方法来做到这一点的AppDelegate喜欢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......也不是它们在这里的用途.

我的意思是:当应用程序进入后台时,我不知道我的用户是哪个视图.回来,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,例如更新视图？

我会理解,如果在每个视图控制器中的那些方法,但在这里,我没有看到它们可以用于具体方式...

你能帮助我理解在这些方法中实现内容的方法吗？

Answer 1

UIApplicationDidEnterBackgroundNotification当应用程序进入后台时,每个对象都会收到通知.因此,当应用程序进入后台时运行一些代码,您只需要在任何地方收听该通知:

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

当你不再需要听它时,不要忘记释放听众:

[[NSNotificationCenter defaultCenter] removeObserver:self];

最好的,您可以使用以下通知播放相同的方式:

• UIApplicationDidEnterBackgroundNotification
• UIApplicationWillEnterForegroundNotification
• UIApplicationWillResignActiveNotification
• UIApplicationDidBecomeActiveNotification

Answer 2

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,您可以确保在需要时方法将触发类(在本例中为应用程序的App Delegate).

作为一个学习过程,你为什么不把NSLog放在这些方法中去看它们何时被解雇？

- (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");
}