[swift] How to update the constant height constraint of a UIView programmatically?

I have a UIView and I set the constraints using Xcode Interface Builder.

Now I need to update that UIView instance's height constant programmatically.

There is a function that goes like myUIView.updateConstraints(), but I don't know how to use it.

Drag the constraint into your VC as an IBOutlet. Then you can change its associated value (and other properties; check the documentation):

@IBOutlet myConstraint : NSLayoutConstraint!
@IBOutlet myView : UIView!

func updateConstraints() {
    // You should handle UI updates on the main queue, whenever possible
    DispatchQueue.main.async {
        self.myConstraint.constant = 10
        self.myView.layoutIfNeeded()
    }
}

To update a layout constraint you only need to update the constant property and call layoutIfNeeded after.

myConstraint.constant = newValue
myView.layoutIfNeeded()

You can update your constraint with a smooth animation if you want, see the chunk of code below:

heightOrWidthConstraint.constant = 100
UIView.animate(withDuration: animateTime, animations:{
self.view.layoutIfNeeded()
})

If the above method does not work then make sure you update it in Dispatch.main.async{} block. You do not need to call layoutIfNeeded() method then.

Create an IBOutlet of NSLayoutConstraint of yourView and update the constant value accordingly the condition specifies.

//Connect them from Interface 
@IBOutlet viewHeight: NSLayoutConstraint! 
@IBOutlet view: UIView!

private func updateViewHeight(height:Int){
   guard let aView = view, aViewHeight = viewHeight else{
      return
   }
   aViewHeight.constant = height
   aView.layoutIfNeeded()
}

If you have a view with multiple constrains, a much easier way without having to create multiple outlets would be:

In interface builder, give each constraint you wish to modify an identifier:

Then in code you can modify multiple constraints like so:

for constraint in self.view.constraints {
    if constraint.identifier == "myConstraint" {
       constraint.constant = 50
    }
}
myView.layoutIfNeeded()

You can give multiple constrains the same identifier thus allowing you to group together constrains and modify all at once.

Change HeightConstraint and WidthConstraint Without creating IBOutlet.

Note: Assign height or width constraint in Storyboard or XIB file. after fetching this Constraint using this extension.

You can use this extension to fetch a height and width Constraint:

extension UIView {

var heightConstraint: NSLayoutConstraint? {
    get {
        return constraints.first(where: {
            $0.firstAttribute == .height && $0.relation == .equal
        })
    }
    set { setNeedsLayout() }
}

var widthConstraint: NSLayoutConstraint? {
    get {
        return constraints.first(where: {
            $0.firstAttribute == .width && $0.relation == .equal
        })
    }
    set { setNeedsLayout() }
}

}

You can use:

yourView.heightConstraint?.constant = newValue 

First connect the Height constraint in to our viewcontroller for creating IBOutlet like the below code shown

@IBOutlet weak var select_dateHeight: NSLayoutConstraint!

then put the below code in view did load or inside any actions

self.select_dateHeight.constant = 0 // we can change the height value

if it is inside a button click

@IBAction func Feedback_button(_ sender: Any) {
 self.select_dateHeight.constant = 0

}