- (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];
    
}