没有使用dispatch_async调用并重复NSTimer的方法 [英] method not called with dispatch_async and repeating NSTimer

问题描述

我正在开发一个应用程序，我希望使用 dispatch_async 在单独的队列中调用方法。我希望在一定的时间间隔后重复调用该方法。但是这个方法没有被调用。

I am developing an app where i want to call method in separate queue using dispatch_async. I want to call that method repeatedly after certain interval of time. But the method is not getting called.

我不知道什么是错的。这是我的代码：

I don't know whats wrong. Here is my code:

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 ");
}

推荐答案

如果你想重复计时器要在 dispatch_queue_t 上调用，请使用 dispatch_source_create ，带有DISPATCH_SOURCE_TYPE_TIMER：

If you want a repeating timer to be invoked on a dispatch_queue_t, use dispatch_source_create with a 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);

创建一个每20秒运行一次的计时器（第三个参数为dispatch_source_set_timer ），余地为一秒钟（第四个参数为 dispatch_source_set_timer ）。

That creates a timer that runs once every 20 seconds (3rd parameter to dispatch_source_set_timer), with a leeway of a one second (4th parameter to dispatch_source_set_timer).

要取消此计时器，请使用 dispatch_source_cancel ：

To cancel this timer, use dispatch_source_cancel:

dispatch_source_cancel(timer);

这篇关于没有使用dispatch_async调用并重复NSTimer的方法的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！