iOS AppDelegate方法梳理，监听进程在后台、被杀死事件 —— HERO博客

AppDelegate中一些常用方法：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    NSLog(@"启动程序，didFinishLaunchingWithOptions");
    
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    NSLog(@"将变为非活跃状态，applicationWillResignActive");
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    NSLog(@"进入后台，applicationDidEnterBackground");
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    NSLog(@"由后台进入前台，applicationWillEnterForeground");
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    NSLog(@"变为活跃状态，applicationDidBecomeActive");
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    NSLog(@"程序被杀死，applicationWillTerminate");
}

- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)(void))completionHandler
{
    NSLog(@" 应用处于后台，所有下载任务完成调用，handleEventsForBackgroundURLSession");
}

当进入后台，想继续进行操作，如果没有注册后台任务，可实现如下代码： 

先定义一个后台任务标识：UIBackgroundTaskIdentifier backgroundTaskIdentifier;

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    backgroundTaskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^(){
        // 程序在进入后台一定时间后（application.backgroundTimeRemaining，我测试是180秒），若还未结束后台任务，则会响应该回调，若已结束，则不会进入该回调
        NSLog(@"beginBackgroundTaskWithExpirationHandler");
    }];
    
    // 这里进行需要的操作，可在操作完成调用endBackgroundTask结束后台任务
    [NSTimer scheduledTimerWithTimeInterval:1.f target:self selector:@selector(timerAction) userInfo:nil repeats:YES];
}

- (void)timerAction
{
    static int a = 0;
    if (a == 100) [self endBackgroundTask];
    NSLog(@"a : %d", a++);
}

- (void)endBackgroundTask
{
    [[UIApplication sharedApplication] endBackgroundTask:backgroundTaskIdentifier];
    backgroundTaskIdentifier = UIBackgroundTaskInvalid;
}

监听进程被杀死时，会发现， 程序处于前台被杀死时会调用applicationWillTerminate:方法，程序处于后台时，并不会调用，需要实现如下代码：

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // 实现如下代码，才能使程序处于后台时被杀死，调用applicationWillTerminate:方法
    [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^(){}];
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    NSLog(@"程序被杀死，applicationWillTerminate");
}

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