// 创建一个和屏幕大小相同的window，记住[UIScreen mainScreen].bounds 是获取当前屏幕大小

    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];

    // 设置window的背景颜色

    self.window.backgroundColor = [UIColor grayColor];

    // 将window设置上，并让window显示

    [self.window makeKeyAndVisible];

    /*

    // 打印屏幕大小，使用NSStringFromCGRect()

    NSLog(@"%@", NSStringFromCGRect([UIScreen mainScreen].bounds));

    // 添加一小块视图到屏幕上

    // 1. 申请空间，并初始化大小

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(20, 20, 200, 200)];

    // 2. 设置view相关属性

    view.backgroundColor = [UIColor whiteColor];

    view.bounds = CGRectMake(20, 0, 200, 200);

    // 3. 添加到window上

    // 添加view到_window上，给_window发送消息

    // 将一个view添加到window上时，view的引用计数会+1

    [_window addSubview:view];

    // 4. 发送一次release消息

    [view release];

    UIView *view2 = [[UIView alloc] initWithFrame:CGRectMake(20, 20, 100, 100)];

    view2.backgroundColor = [UIColor redColor];

    [view addSubview:view2];

    [view2 release];

    // 使用中心点更改view的位置

//    view.center = CGPointMake(320 / 2, 568 / 2);

//    NSLog(@"%@", NSStringFromCGPoint(view.center));

//    view2.center = CGPointMake(view.frame.size.width / 2, view.frame.size.height / 2);

//    NSLog(@"%@", NSStringFromCGPoint(view2.center));

    */

    //view1 蓝色

    UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 200, 200)];

    view1.backgroundColor = [UIColor blueColor];

    view1.tag = 1000;

    [_window addSubview:view1];

    [_window viewWithTag:1000].backgroundColor = [UIColor yellowColor];//根据tag值，取出view 设置

    [view1 release];

    //view2 红色

    UIView *view2 = [[UIView alloc] initWithFrame:CGRectMake(80, 20, 100, 400)];

    view2.backgroundColor = [UIColor redColor];

    view2.tag = 1001;

    [_window addSubview:view2];

    //[_window insertSubview:view2 belowSubview:view1];//将红 插到 蓝的底下

    [view2 release];

    //view3 紫色

    UIView *view3 = [[UIView alloc] initWithFrame:CGRectMake(30, 30, 100, 100)];

    view3.backgroundColor = [UIColor purpleColor];

    view3.tag = 1002;

    view3.hidden = NO;

    view3.center = CGPointMake(160, 160);//设置中心点属性

    [_window addSubview:view3];

    //[_window insertSubview:view3 atIndex:1];

    [view3 release];

    // 将view提到最上层

    //[_window bringSubviewToFront:view2];

    // 将view放到最下层

   // [_window sendSubviewToBack:view2];

    // 将view2从父视图上移除

    //[view2 removeFromSuperview];

    NSLog(@"%@", view1.superview);

    NSLog(@"%@", _window.subviews);

    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(50, 350, 200, 40)];

    label.text = @"cai bi";

    label.font = [UIFont fontWithName:@"Helvetica-Bold" size:40];

    [_window addSubview:label];

    [label release];

    // 

    [_window viewWithTag:1000].alpha = 0.5;

UIview lianxi