动画调整UIView和子视图大小的更好方法？

屏幕截图示例：

动画调整包含子视图的UIView大小的更好方法是什么？

What is a better way to animate the resizing of a UIView that includes subviews?

我当前的方法：

在屏幕截图中，父UIView（橙色）有一个子视图UILabel（黄色+自动调整大小）。 animateWithDuration 正在调整父UIView框架的大小。此方法的问题是它没有为子视图的大小调整设置动画。它会突然改变，它应该动画缩放。

In the screen capture, the parent UIView (orange) has a subview UILabel (yellow + autoresizing). animateWithDuration is animating the resizing of the parent UIView's frame. The problem with this method is it does not animate the resizing of the subview. It abruptly changes, where it should scale animatedly.

是否明确地为子视图设置动画，或者是否有更有效的方法？ （例如CGAffineTransform？）

Is explicitly animating the subview best, or is there a more efficient method? (e.g. CGAffineTransform?)

示例代码：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    self.parentView = [[UIView alloc] initWithFrame:CGRectMake(10, 100, 200, 200)];
    self.parentView.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:self.parentView];

    self.childLabel = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 180, 180)];
    self.childLabel.autoresizingMask = UIViewAutoresizingFlexibleWidth |
                                     UIViewAutoresizingFlexibleHeight;
    self.childLabel.backgroundColor = [UIColor yellowColor];
    [self.parentView addSubview:self.childLabel];

    [NSTimer scheduledTimerWithTimeInterval:2
                                     target:self
                                   selector:@selector(randomizeParentViewSize)
                                   userInfo:nil
                                    repeats:YES];
}

- (void)randomizeParentViewSize {
    CGFloat width = arc4random_uniform(100) + 50;
    CGFloat height = arc4random_uniform(100) + 50;

    [UIView animateWithDuration:1.5f
                          delay:0.0f
                        options:0
                     animations:^{
                         self.parentView.frame = CGRectMake(10, 50 + height, width, height);
                     }
                     completion:^(BOOL finished) {
                     }];
}