iOS中定时任务的三种方法

1.SEL:对方法的包装, 使用@selector(方法名)包装一个SEL数据

// 2.0s以后会自动调用self的hidHUD方法

 [self performSelector:@selector(hideHUD) withObject:nil afterDelay:2.0];

-(void)hideHUD{

self.hud.alpha = 0.0;

2.GCD

        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

            self.hud.alpha = 0.0;

        });

3.NSTimer

[NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(hideHUD) userInfo:nil repeats:NO];

-(void)hideHUD{

self.hud.alpha = 0.0;