iOS程序进入后台后仍可运行定时器

网上看到一篇iOS程序进入后台仍可运行定时器的方法,在此做一个记录 原文,也许以后可以用到

1.在Info.plist中，添加"Required background modes"键，value为：App plays audio

2.在AppDelegate 的 application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions中添加代码

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];    // Override point for customization after application launch.
    NSError *setCategoryErr = nil;
    NSError *activationErr  = nil;
    [[AVAudioSession sharedInstance]
     setCategory: AVAudioSessionCategoryPlayback
     error: &setCategoryErr];
    [[AVAudioSession sharedInstance]
     setActive: YES
     error: &activationErr];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];    return YES;
}

3在AppDelegate进入后台的方法applicationDidEnterBackground:(UIApplication *)application添加代码

- (void)applicationDidEnterBackground:(UIApplication *)application{
    UIApplication*   app = [UIApplication sharedApplication];
    __block    UIBackgroundTaskIdentifier bgTask;
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        dispatch_async(dispatch_get_main_queue(), ^{            
            if (bgTask != UIBackgroundTaskInvalid) {
                bgTask = UIBackgroundTaskInvalid;
            }
        });
    }];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        dispatch_async(dispatch_get_main_queue(), ^{           
           if (bgTask != UIBackgroundTaskInvalid)  {
                 bgTask = UIBackgroundTaskInvalid;
            }
        });
    });
}