UIStackView Hiding/UnHiding arrangedSubView issue

问题:

I am hiding and unhiding dropDownView(UIView consisting of textfield and button) based on Segment tapped in Segment Control. Following is the view hierarchy :-

Following is the code which hides/unhides dropDownView :-

 private func animateView(view: UIStackView, toHidden hidden: Bool) {
    UIView.animate(withDuration: 0.25) 
    {
    let firstView = view.arrangedSubviews[0]
    firstView.isHidden = hidden
    }
    }
func segmentValueChanged(_ sender: UISegmentedControl) {
        let segmentSelected = segmentControl.selectedSegmentIndex
        switch segmentSelected {
        case 0:
            animateView(view: mainStackView, toHidden: true)
        case 1:
         animateView(view: mainStackView, toHidden: true)
        case 2:
            animateView(view: mainStackView, toHidden: true)
        case 3:
           animateView(view: mainStackView, toHidden: false)
        default:
            break
        }
    }

Problem which I am facing is after changing segments over 10-15 times the above code stops working and DropDown View overlaps with Segment Control and I am not sure why. Any help to understand this issue is appreciated.

Also I have already tried
1. setNeedsLayout,
2. setNeedsDisplay and
3. reducing priority to height constraint of dropDownView to 999 from 1000

回答1:

Try without your animate function as stackView should animate hiding and unhiding anyway. Add a check for hidden status and only change it if necessary:

func segmentValueChanged(_ sender: UISegmentedControl) {
    let segmentSelected = segmentControl.selectedSegmentIndex
    let dropDown = mainStackView.arrangedSubviews.first!

    switch segmentSelected {
        case 0, 1, 2:
            if !dropDown.isHidden {
                dropDown.isHidden = true
            }
        case 3:
            if dropDown.isHidden {
                dropDown.isHidden = false
            }
        default:
            break
    }

}

回答2:

Try this one below. Hope will solve your problem.

private func animateView(view: UIStackView, toHidden hidden: Bool) {
    let firstView = view.arrangedSubviews[0]
    UIView.animate(withDuration: 0.25) {
        firstView.isHidden = hidden
        view.layoutIfNeeded()
    }
}

回答3:

Following is the solution that I implemented which seems to work:-

private func animateView(view: UIStackView, toHidden hidden: Bool) {
        if !hidden
        {
          mainStackView.insertArrangedSubview(view, at: 0)
          view.isHidden = true
          UIView.animate(withDuration: 0.25, animations: {
            view.isHidden = false
          })
        } else {
            let firstView = mainStackView.arrangedSubviews[0]
            UIView.animate(withDuration: 0.25, animations: {
                if firstView == view {
                    firstView.isHidden = true
                }
            }, completion: { [weak self] _ in
                if firstView == view {
                    self?.mainStackView.removeArrangedSubview(firstView)
                    firstView.removeFromSuperview()
                }
            })
        }
    }

Creating DropDown View programmatically (Instead of creating in storyboard) and removing same on every completion. I am not marking this answer correct as its a workaround. I want to understand why storyboard dropDownView fails after 10-15 tries.