没有使用dispatch_async调用并重复NSTimer的方法

Question

我正在开发一个应用程序,我想在单独的队列中使用调用方法dispatch_async.我希望在一定的时间间隔后重复调用该方法.但是方法没有被调用.

我不知道什么是错的.这是我的代码:

dispatch_async( NotificationQueue, ^{

        NSLog(@"inside queue");
        timer = [NSTimer scheduledTimerWithTimeInterval: 20.0
                                                 target: self
                                               selector: @selector(gettingNotification)
                                               userInfo: nil
                                                repeats: YES];

        dispatch_async( dispatch_get_main_queue(), ^{
            // Add code here to update the UI/send notifications based on the
            // results of the background processing

        });
    });

-(void)gettingNotification {
    NSLog(@"calling method ");
}

Answer 1

如果你想成为一个调用重复的计时器dispatch_queue_t,使用dispatch_source_create了DISPATCH_SOURCE_TYPE_TIMER:

dispatch_queue_t  queue = dispatch_queue_create("com.firm.app.timer", 0);
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), 20ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC);

dispatch_source_set_event_handler(timer, ^{

    // stuff performed on background queue goes here

    NSLog(@"done on custom background queue");

    // if you need to also do any UI updates, synchronize model updates,
    // or the like, dispatch that back to the main queue:

    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"done on main queue");
    });
});

dispatch_resume(timer);

这创建了一个每20秒运行一次的计时器(第3个参数dispatch_source_set_timer),余地为1秒(第4个参数dispatch_source_set_timer).

要取消此计时器,请使用dispatch_source_cancel:

dispatch_source_cancel(timer);