UIView *view1=[[UIView alloc] initWithFrame:CGRectMake(50, 50, 100, 100)];

    view1.backgroundColor=[UIColor yellowColor];

    view1.tag=1;

    [self.window addSubview:view1];

    UIView *view2=[[UIView alloc] initWithFrame:CGRectMake(10, 10, 20, 20)];

    view2.backgroundColor=[UIColor greenColor];

    view2.tag=2;

    view2.alpha=0.2;//更改透明度，会影响到子视图显示

    [view1 addSubview:view2];//视图嵌套

    UIView *view3=[[UIView alloc] initWithFrame:CGRectMake(10, 10, 30, 30)];

    view3.backgroundColor=[UIColor grayColor];

    view3.tag=3;

    [view2 addSubview:view3];//视图3颜色受父类影响

    UIView *view5=[[UIView alloc] initWithFrame:CGRectMake(50, 50, 30, 30)];

    view5.backgroundColor=[UIColor grayColor];

    view5.tag=5;

    [view1 addSubview:view5];

    UIView *view4=[[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];

    view4.backgroundColor=[UIColor blackColor];

    view4.hidden=YES;//隐藏视图，也会影响到子类

    [view1 addSubview:view4];

    UIView *view6=[[UIView alloc] initWithFrame:CGRectMake(80, 80, 10, 10)];

    view6.backgroundColor=[UIColor colorWithRed:1 green:0 blue:0 alpha:0.5];//

    [view1 addSubview:view6];

    UIView *view=[self.window viewWithTag:2];//通过tag获取指定视图

    view.backgroundColor=[UIColor redColor];

    //自定义视图

    MyView *myview=[[MyView alloc] initWithFrame:CGRectMake(150, 150, 100, 100)];

    [self.window addSubview:myview];

    [self.window makeKeyAndVisible];