当两个或多个视图同时添加头一个视图的时候，会发生什么情况？

//视图1

self.VV1 = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 100, 100)];

self.VV1.backgroundColor = [UIColor redColor];

[self.view addSubview:self.VV1];

//视图2

self.VV2 = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 200)];

self.VV2.backgroundColor = [UIColor greenColor];

[self.view addSubview:self.VV2];

//视图3

self.VV3 = [[UIView alloc] initWithFrame:CGRectMake(100, 400, 200, 200)];

self.VV3.backgroundColor = [UIColor blueColor];

[self.view addSubview:self.VV3];

//视图2添加视图1

[self.VV2 addSubview:self.VV1];

//视图3添加视图1

[self.VV3 addSubview:self.VV1];