在子类中代码创建控件，显示在父容器内，并动态删除掉

- (IBAction)btnDown:(id)sender {

    //取到父类

    UIView *viewW=self.superview;

    //代码创建lbl

    UILabel *lblMesg=[[UILabel alloc] init];

    lblMesg.backgroundColor= [UIColor blackColor];

    [lblMesg.layer setCornerRadius:5];

    [lblMesg.layer setMasksToBounds:YES];

    lblMesg.alpha=0;

    lblMesg.text=@"下在下载";

    lblMesg.textAlignment=NSTextAlignmentCenter;

    lblMesg.font=[UIFont boldSystemFontOfSize:17];

    lblMesg.textColor=[UIColor whiteColor];

    lblMesg.frame=CGRectMake(0,0 , 200, 20);

    lblMesg.center=viewW.center;

    [viewW addSubview:lblMesg];

    [UIView animateWithDuration:2.0 animations:^{

        lblMesg.alpha=0.8;

    }];

    [UIView animateWithDuration:1.5 animations:^{

        lblMesg.alpha=0.8;

    } completion:^(BOOL finished) {

        if (finished) {

            //等1.5秒后再启动另外一个动画

            //delay=等1.5秒后再执行

            //UIViewAnimationOptionCurveLinear 匀速执行

            [UIView animateWithDuration:1.5 delay:1.5 options:UIViewAnimationOptionCurveLinear animations:^{

                lblMesg.alpha=0;

          4000   } completion:^(BOOL finished) {

                [lblMesg removeFromSuperview];

                NSLog(@"把这个类从父类中删除");

            }];

        }

    }];

}