创建提示信息

    label.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:0.5];
    label.textColor = [UIColor whiteColor];
    label.font = [UIFont systemFontOfSize:14];
    label.layer.cornerRadius = 10;
    label.text = string;
    label.textAlignment = NSTextAlignmentCenter;
    [self.view addSubview:label];
    
    //设置动画
    CATransition *transion = [CATransition animation];
    transion.type = kCATransitionFade;
    [label.layer addAnimation:transion forKey:nil];
    
    dispatch_time_t time = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1.0*NSEC_PER_SEC));
    dispatch_after(time, dispatch_get_main_queue(), ^{
        [label removeFromSuperview];
    });