iOS:GCD进行延迟执行任务

通过GCD可以延迟执行任务，代码如下：

double time = 2.0;    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)time*NSEC_PER_SEC);    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){        [self method];    });