仿微博下拉提示

//初始化，将lab添加进入一个Img
        UIImage *img = [[UIImage imageNamed:@"timeline_new_status_background.png"] stretchableImageWithLeftCapWidth:5 topCapHeight:5];
        _barView = [[UIImageView alloc] initWithImage:img];
        _barView.frame = CGRectMake(5, -40, 320-10, 40);
        [self.view addSubview:_barView];
        
        UILabel *label = [[UILabel alloc] initWithFrame:CGRectZero];
        label.tag = 100;
        label.font = [UIFont systemFontOfSize:16.0f];
        label.textColor = [UIColor whiteColor];
        label.backgroundColor = [UIColor clearColor];
        [_barView addSubview:label];
        [label release];

　　

//显示出来2秒    
    UILabel *label = (UILabel *)[_barView viewWithTag:100];
    label.text = [NSString stringWithFormat:@"%d条微博更新",10];
    [label sizeToFit];
    CGRect frame = label.frame;
    frame.origin = CGPointMake((_barView.frame.size.width - frame.size.width)/2, (_barView.frame.size.height - frame.size.height)/2);
    label.frame = frame;

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

　　

//慢慢消失   
    [UIView animateWithDuration:0.6 animations:^{
        CGRect frame = _barView.frame;
        frame.origin.y = 5;
        _barView.frame = frame;
    } completion:^(BOOL finished){
        if (finished) {
            [UIView beginAnimations:nil context:nil];
            [UIView setAnimationDelay:1.0];
            [UIView setAnimationDuration:0.6];
            CGRect frame = _barView.frame;
            frame.origin.y = -40;
            _barView.frame = frame;
            [UIView commitAnimations];
        }
    }];