iOS 延迟1.5s 执行方法

   1. [self performSelector:@selector(fangfa) withObject:nil afterDelay:0.5];  // performSelector
  2.  [NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(fangfa) userInfo:nil repeats:NO]; //NSTimer
   //GCD
//在主线程延迟执行 一般用这个

 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
   [self delayDo:@”GCD”];
   });
//在子线程延迟执行
   dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(5 * NSEC_PER_SEC)), dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
   [self delayDo:@”Global-GCD”];
   });