// 画纸

    UIView *containerView = [[UIView alloc] initWithFrame:self.window.bounds];

    containerView.backgroundColor = [UIColor whiteColor];

    [self.window addSubview:containerView];

    [containerView release];

    UIView *blueView = [[UIView alloc] initWithFrame:CGRectMake(100, 200, 200, 200)];

    blueView.backgroundColor = [UIColor blueColor];

    // 设置中心点的位置

    blueView.center = self.window.center;

    // 设置不透明度为50%

    blueView.alpha = 0.5;

    // 给蓝色视图添加一个标记

    blueView.tag = 101;

    [containerView addSubview:blueView];

    // 获取蓝色视图的父视图

    NSLog(@"superview is %@ containerView is %@",blueView.superview, containerView);

    NSLog(@"subviews is %@ blueView is %@",containerView.subviews, blueView);

    // 通过tag找到blueView并且将其颜色改为红色

    [containerView viewWithTag:101].backgroundColor = [UIColor redColor];

    [blueView release];

    UIView *yellowView = [[UIView alloc] initWithFrame:CGRectMake(200, 200, 100, 100)];

    yellowView.backgroundColor = [UIColor yellowColor];

    // 在某一个下标下让父视图插入一个新的子视图

    [containerView insertSubview:yellowView atIndex:1];

    [yellowView release];

    // 移除试图，把某一个视图从父视图中移除

    [blueView removeFromSuperview];