具有动态高度的子视图的自动布局 UIScrollView

我在使用自动布局约束时遇到了 UIScrollView 的问题.我有以下视图层次结构，通过 IB 设置约束:

I'm having troubles with UIScrollView using auto layout constraints. I have the following view hierarchy, with constraints set through IB:

- ScrollView (leading, trailing, bottom and top spaces to superview)
-- ContainerView (leading, trailing, bottom and top spaces to superview)
--- ViewA (full width, top of superview)
--- ViewB (full width, below ViewA)
--- Button (full width, below ViewB)

ViewA 和 ViewB 的初始高度为 200 点，但可以通过单击垂直扩展至 400 点的高度.ViewA 和 ViewB 通过更新它们的高度约束(从 200 到 400)来扩展.这是相应的片段:

The ViewA and ViewB have initial heights of 200 points, but it can be expended vertically to an height of 400 points by clicking on it. ViewA and ViewB are expanded by updating their height constraint (from 200 to 400). Here is the corresponding snippet :

if(self.contentVisible) {
    heightConstraint.constant -= ContentHeight;
    //   additional View's internal constraints update to hide additional content 
    self.contentVisible = NO;
} else {
    heightConstraint.constant  = ContentHeight;
    //   additional View's internal constraints update to show additional content
    self.contentVisible = YES;
}

[self.view setNeedsUpdateConstraints];
[UIView animateWithDuration:.25f animations:^{
    [self.view layoutIfNeeded];
}];

我的问题是，如果两个视图都展开，我需要能够滚动才能看到整个内容，而现在滚动不起作用.如何使用约束来更新滚动视图以反映 ViewA 和 ViewB 高度的变化?

My problem is that if both views are expanded, I need to be able to scroll to see the whole content, and right now the scroll is not working. How can I manage to update the scroll view using constraints to reflect the changes of ViewA and ViewB heights ?

目前我能想到的唯一解决方案是在动画后手动设置ContainerView的高度，这将是ViewA ViewB Button的高度之和.但我相信有更好的解决方案?

The only solution I can think of so far is to manually set the height of the ContainerView after the animation, which will be the sum of the heights of ViewA ViewB Button. But I believe there is a better solution?

谢谢