第一种: performSelector
[self performSelector:@selector(run) withObject:nil afterDelay:2.0];
第二种: NSTimer
[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(run) userInfo:nil repeats:YES];
第三种: GCD
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self run];
});
注 : run是方法
