iOS 8 Custom Keyboard: Changing the height without warning 'Unable to simultaneously satisfy constraints...'

Question

There are several SO answers about how to change Custom Keyboard height. Some of them work for example here but those that work lead to constrains conflict error printed to console output:

Unable to simultaneously satisfy constraints... 
Will attempt to recover by breaking constraint...

Here is my very simple keyboard controller that sets custom keyboard height (is Swift):

class KeyboardViewController: UIInputViewController {
    private var heightConstraint: NSLayoutConstraint?
    private var dummyView: UIView = UIView()

    override func updateViewConstraints() {
        super.updateViewConstraints()

        if self.view.frame.size.width == 0 || self.view.frame.size.height == 0 || heightConstraint == nil {
            return
        }
        inputView.removeConstraint(heightConstraint!)
        heightConstraint!.constant = UIInterfaceOrientationIsLandscape(self.interfaceOrientation) ? 180 : 200
        inputView.addConstraint(heightConstraint!)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.dummyView.setTranslatesAutoresizingMaskIntoConstraints(false)
        self.view.addSubview(self.dummyView)

        view.addConstraint(NSLayoutConstraint(item: self.dummyView, attribute: .Left, relatedBy: .Equal, toItem: self.view, attribute: .Left, multiplier: 1.0, constant: 0.0))
        view.addConstraint(NSLayoutConstraint(item: self.dummyView, attribute: .Bottom, relatedBy: .Equal, toItem: self.view, attribute: .Bottom, multiplier: 1.0, constant: 0.0))

        heightConstraint = NSLayoutConstraint(item: view, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: 0.0)
    }
}

This produces the annoying output error that my constrain heightConstraint that I added in updateViewConstraints is in conflict with constrain identified as UIView-Encapsulated-Layout-Height.

I tried to remove conflicting constant (UIView-Encapsulated-Layout-Height) in updateViewConstraints as follows:

let defaultHeightConst = inputView.constraints().filter() {c in (c as? NSLayoutConstraint)?.identifier == "UIView-Encapsulated-Layout-Height"}.first as? NSLayoutConstraint
if defaultHeightConst != nil {
    inputView.removeConstraint(defaultHeightConst!
}

This did not help, the output warning is still there. How do I solve this? Specifically, what can I do to get rid of the output error message?

Answer 1

Try setting heightConstraint priority to less than 1000. Some thing like blow :

heightConstraint.priority = 990

OR

heightConstraint.priority = 999