maskView配合带alpha通道图片

1.比CAGradientLayer高效
2.可以加载多张图片，并实现动画特效

    UIImageView  *backgroundView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];    backgroundView.image = [UIImage imageNamed:@"background"];    backgroundView.center = self.view.center;    [self.view addSubview:backgroundView];    UIImageView  *baseView = [[UIImageView alloc] initWithFrame:backgroundView.frame];    baseView.image = [UIImage imageNamed:@"base"];    [self.view addSubview:baseView];    //创建maskView作为容器    UIView *mask = [[UIView alloc] initWithFrame:baseView.bounds];    baseView.maskView = mask;    //maskView中的subView1    UIImageView *picOne = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 100, 400)];    picOne.image = [UIImage imageNamed:@"1"];    [mask addSubview:picOne];    //maskView中的subView2    UIImageView *picTwo = [[UIImageView alloc] initWithFrame:CGRectMake(0, -200, 100, 400)];    picTwo.image = [UIImage imageNamed:@"2"];    [mask addSubview:picTwo];    [UIView animateWithDuration:2.f animations:^{        CGRect oneFrame = picOne.frame;        oneFrame.origin.y -= 400;        picOne.frame = oneFrame;        CGRect twoFrame = picTwo.frame;        twoFrame.origin.y -= 400;        picTwo.frame = twoFrame;    }];

github上开源的代码可查看