根据内容动画 UIScrollView 的高度

Question

My situation:

I have a horizontal ScrollView containing a StackView. Inside this StackView there are some Views, that can be expanded/collapsed.

When I want to expand one of these Views, I first unhide some subViews in the View. After that I need to change the height of the ScrollView based on the new height of this View.

But this is not working...

I try this code:

        UIView.animate(withDuration: 0.3) { [self] in
            // Toggle hight of all subViews
            stackView.arrangedSubviews.forEach { itemView in
                guard let itemView = itemView as? MyView else { return }
                itemView.toggleView()
            }
            
            // Now update the hight of the StackView
            // But here the hight is always from the previous toggle
            let height = self.stackView.arrangedSubviews.map {$0.frame.size.height}.max() ?? 0.0
            print(height)

            heightConstraint.constant = height
        }

This code nicely animates, but always to the wrong height. So the ScrollView animates to collapsed when it should be expanded and expanded when it should be collapsed.

Anyone with on idea how to solve this?

Answer 1

The problem is that, whatever you are doing here:

itemView.toggleView()

may have done something to change the height a view, but then you immediately call:

let height = self.stackView.arrangedSubviews.map {$0.frame.size.height}.max() ?? 0.0

before UIKit has updated the frames.

So, you can either track your own height property, or...

get the frame heights after the update - such as with:

    DispatchQueue.main.async {
        let height = self.stackView.arrangedSubviews.map {$0.frame.size.height}.max() ?? 0.0
        print("h", height)
        self.scrollHeightConstraint.constant = height
        UIView.animate(withDuration: 0.3) {
            self.view.layoutIfNeeded()
        }
    }