Swift - Constraints issue in expandable TableViewCell

问题

I'm creating an expandable cell with labels and picker view

xib

Cell Implementation

class PickerViewCell: UITableViewCell {

@IBOutlet weak var detailLabel: UILabel!
@IBOutlet weak var titleLabel: UILabel!
@IBOutlet weak var height: NSLayoutConstraint!
@IBOutlet weak var picker: UIDatePicker!
var isExpanded:Bool = false
    {
        didSet
        {
            if isExpanded == false{
                self.height.constant = 0.0
                self.picker.hidden = true

            }
            else{
                self.height.constant = 200.0
                self.picker.hidden = false
            }
        }
}
override func awakeFromNib() {
    self.height.constant = 0.0
    super.awakeFromNib()
}

Delegate method

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    guard let cell = tableView.cellForRowAtIndexPath(indexPath) as? PickerViewCell else { return }

    cell.isExpanded = !cell.isExpanded
    print(cell.isExpanded)
    UIView.animateWithDuration(0.3) {
        cell.contentView.layoutIfNeeded()
    }

    tableView.beginUpdates()
    tableView.endUpdates()

    tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: UITableViewScrollPosition.Top, animated: true)
}

I keep getting runtime warining about breaking constraints.

I set up a symbolic breakpoint and what I found out is that this line

self.height.constant = 200.0

inside cell implementation is the reason of the warning.

However, I found out that it happens only during the first tap on a given cell, after the initial tap I can tap multiple times, expanding and closing it each time, and the warning does not occur. Should I even care about this runtime warning?

EDIT:

I forgot to show datePicker constraints including those on height and aspect ratio:

Also it's worth to mention that I utilize

self.tableView.estimatedRowHeight = 100.0
self.tableView.rowHeight = UITableViewAutomaticDimension

in my viewController

回答1:

You set datePicker height to 200, but then set cell height to 200 too. But cell height is datePicker's height + 10 + label's height. So those constraints conflict to each other.