iOS 定时器的使用 在后台运行定时器

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1.在APPDelegate的didFinishLaunchingWithOptions中设置

[session setCategory:AVAudioSessionCategoryPlayback error:nil];
[[AVAudioSession sharedInstance] setActive:NO withOptions:AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation error:nil];

2.在APPDelegate的applicationDidEnterBackground中设置

//处理后台定时器关闭的问题
    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;
            }
        });
    });

3.使用定时器

	// 创建定时器
	count = 0;
	__weak  typeof(self) weakSelf = self;
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC, 0 * NSEC_PER_SEC);
    dispatch_source_set_event_handler(timer, ^{
	    count ++;
         weakSelf.timeLabel.text = [NSString stringWithFormat:@"%ld", count];
        }
    });
    dispatch_resume(timer);

	// 停止定时器
	dispatch_source_cancel(timer);

GCD延迟执行

	dispatch_time_t delayTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC));
    dispatch_after(delayTime, dispatch_get_main_queue(), ^{
    });

NSTimer

	// 创建定时器
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(test) userInfo:nil repeats:YES];

    // 停止定时器
    [timer invalidate];