iOS 使用 dispatch_source_t 实现计时器功能

我们经常要用倒计时器，方案有很多，如NSTimer, CADisplayLink(比较精密的计时器),

现在我们看一下使用GCD实现定时器，上代码

创建定时器

- (dispatch_source_t)timer{
    if (!_timer) {
        _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0));
        int64_t delayTime = (int64_t)(5*NSEC_PER_SEC);
        dispatch_time_t startTime = dispatch_time(DISPATCH_TIME_NOW, delayTime);
        
        CFTimeInterval time = self.pConfig.timeInterval>self.pConfig.duration?self.pConfig.timeInterval:3;
        uint64_t interval = (uint64_t)(time*NSEC_PER_SEC);
        dispatch_source_set_timer(_timer, startTime, interval, 0);
        
        dispatch_source_set_event_handler(_timer, ^{
            dispatch_async(dispatch_get_main_queue(), ^{
                [self timerHandle];
            });
        });
    }
    return _timer;
}

需要手动开启定时器

- (void)resume{
    if (self.isSuspend) {
        dispatch_resume