iOS 视图层次管理

iOS里的视图其实可以理解为ppt或photoshop里的图层，可以通过设置为最顶层或最底层来达到想要的效果

- (void)viewDidLoad {  
    [super viewDidLoad];  
    // Do any additional setup after loading the view, typically from a nib.  
      
    UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(10, 50, 100, 50)];  
    view1.backgroundColor = [UIColor blueColor];  
    [self.view addSubview:view1];  
      
    UIView *view2 = [[UIView alloc] initWithFrame:CGRectMake(15, 55, 100, 50)];  
    view2.backgroundColor = [UIColor grayColor];  
    [self.view addSubview:view2];  
      
    //如果将下面两行代码都注释掉   view1 会在下面   view2会在上面  
    //  下面这行代码能够将view2  调整到父视图的最下面  
//    [self.view sendSubviewToBack:view2];  
    //将view调整到父视图的最上面  
    [self.view bringSubviewToFront:view1];  
      
}