1.在view1视图上以view1.frame的格式添加view2视图
UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 200, 200)];
view1.backgroundColor = [UIColor greenColor];
[self.window addSubview:view1];
UIView *view2 = [[UIView alloc] initWithFrame:view1.frame];
view2.backgroundColor = [UIColor redColor];
[view1 addSubview:view2];
解答：
①、view1的是将手机屏幕的左上角作为原点
②、view2则是将view1的左上角作为原点
③、可以理解为：view2以view1作为父视图，然后添加
view1视图上一view1.brounds的格式添加视图
UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(50, 50, 200, 200)];
view1.backgroundColor = [UIColor greenColor];
[self.window addSubview:view1];
UIView *view2 = [[UIView alloc] initWithFrame:view1.bounds];
view2.backgroundColor = [UIColor redColor];
[view1 addSubview:view2];
解答：
①、此时view1和view2都是以屏幕的左上角作为原点
②、通俗点说就是view2是在view1视图上拷贝了view1，然后再view1所在的位置上黏贴了view2
3、在self.window视图上以view1.bounds格式添加view2
UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(50, 0, 200, 200)];
view1.backgroundColor = [UIColor greenColor];
[self.window addSubview:view1];
UIView *view2 = [[UIView alloc] initWithFrame:view1.bounds];
view2.backgroundColor = [UIColor redColor];
[self.window addSubview:view2];
view2.alpha = 0.3;
解答：
①、此时的屏幕原本的原点有(0,0),改成了(-50,0);
②、也可以说是将view1的x坐标和y坐标取相反数作为self.window的原点
4、在self.widow视图上一view1.frame格式添加view2
UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(50, 0, 200, 200)];
view1.backgroundColor = [UIColor greenColor];
[self.window addSubview:view1];
UIView *view2 = [[UIView alloc] initWithFrame:view1.frame];
view2.backgroundColor = [UIColor redColor];
[self.window addSubview:view2];
view2.alpha = 0.3;
解答：
①、以view1的创建格式做为view2的格式添加view2
②、通俗说就是view2在view1的位置上拷贝了view1
frame:是基于它父视图的坐标系而言
bounds:就是该视图在自己这套坐标系中的位置以及大小，只会影响自身子视图的位置。
