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];