having trouble changing an auto layout constraint

Question

I want to both resize and relocate an auto layout constraint when there are characters in a textview. Yes, I am using a textview delegate. Yes, the view does layout properly when the view loads. The problem arises when I attempt to resize the view... I can move it how I want (centerX), however when I change the width property the view animates away and disappears...

Here's the code...

paddingView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.5).isActive = true

    NSLayoutConstraint(item: paddingView, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 0.75, constant: 0).isActive = true

    paddingView.heightAnchor.constraint(equalToConstant: 6.0).isActive = true

    bottomConstraint = paddingView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0.0)
    bottomConstraint?.isActive = true

Here's the second part

func textViewDidChange(_ textView: UITextView) {

    let currentString: String = textView.text!
    let length: Int = (currentString.characters.count )

    if length > 0 {

                NSLayoutConstraint(item: paddingView, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 1, constant: 0).isActive = true
            paddingView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.75).isActive = true





    }else{



    }

    UIView.animate(withDuration: 0.2, delay: 0, options: UIViewAnimationOptions.curveEaseOut, animations: {
        self.view.layoutIfNeeded()
    }, completion: { (completed) in

    })

}

Could it be because I am using anchors and NSLayoutConstraints together?

Have you checked your debug output for unsatisfiable constraints? Note that if `textViewDidChange:` is called multiple times, it will keep adding new constraints without removing the previously added ones, which might cause some autolayout issues — crizzis, Jun 01 '17 at 19:35
Yeah, one of my constraints is unsatisfiable. It's the new width constraint and it attempts to fix it by breaking the centerX constraint — Stefan, Jun 01 '17 at 19:46
Look at this: https://stackoverflow.com/questions/19593641/can-i-change-multiplier-property-for-nslayoutconstraint — Lou Franco, Jun 01 '17 at 19:53
You are adding more constraints, not changing the old one. The old multiplier constraint is in conflict with the new one. — Lou Franco, Jun 01 '17 at 19:54

score 1 · Accepted Answer · answered Jun 01 '17 at 19:54

For resizing:You can increase and decrease the size of the textview dynamically by not setting fixed constraints to super view and playing around with compression hugging and resistance priorities. For relocating: Enable and disable constraints at various places in textview delegate

having trouble changing an auto layout constraint

1 Answers1