How To Change Havells Tube Light

How to update the view height with animation programmatically

Common problems of writing NSLayoutConstraint

Hello swift programmers, in this article we will look at how to use NSLayoutConstraint to elegantly handle the resize of view using some animation. let's take an example

In apple notes app if you notice as soon as the keyboard comes up the text fields height changes with sweet animation. which look good to eyes and gives thoughts to the brain how to they do it?

This very common problem with a simple solution. the solution can be used to any UI element like a UIButton, UIImageView, UILable so on and so forth.

Overview:

We will learn how to construct`NSLayoutConstraint`
How to update the NSLayoutConstraint
How to use simple animation

Note

To change the hight of view we need to update the constant value of the constraint. if you add a new constraint it creates the conflict in auto layout and you can see those error in the console like this

                      (                                "<NSLayoutConstraint:0x600002586030 UITextView:0x7ff602006600.height == 520   (active)>",                                "<NSLayoutConstraint:0x6000025fcc80 UITextView:0x7ff602006600.height == 20   (active)>"                                )

Step 1: Add UITextfiled with following constraints

Top, left and right constraints as shown below with your preferred constant value. I am giving it as 16.

          NSLayoutConstraint.activate([          textViewToUse.topAnchor.constraint(equalTo: view.topAnchor, constant: 0),          textViewToUse.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 16),          textViewToUse.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -16),          ])

Step 2: Create height constraint separately and make it accessible within the class.

                      private var            heightConstraint: NSLayoutConstraint?

Also creating default height values

                      lazy            var            textFieldFullHeight:CGFloat = {                                    self.view.frame.size.height - 100          }()                      var            textFieldHalfHeight:CGFloat = 200

Step 3: Add initial value to `heightConstraint`

          heightConstraint = NSLayoutConstraint(item: textViewToUse,                      attribute: .height,                      relatedBy: .equal,                      toItem:            nil,                      attribute: .notAnAttribute,                      multiplier: 1,                      constant: textFieldFullHeight)

Note: you can assign the vlaue at the declaration of `heightConstraint` to avoid option value.

Step 4: Add height Constraint to Textfield

          textViewToUse.addConstraint(heightConstraint!)

Step 5: Listen to keyboard notification

As we are animating the `UITextfield` height based on keyboard appearance status

          //Adding this in viewDidLoad
NotificationCenter.default.addObserver(self, selector:            #selector(keyboardWillShow(notification:)), name: UIResponder.keyboardWillShowNotification, object:            nil)          NotificationCenter.default.addObserver(self, selector:            #selector(keyboardWillHide(notification:)), name: UIResponder.keyboardWillHideNotification, object:            nil)          //Adding this outside viewDidLoad                      @objc            func            keyboardWillShow(notification: NSNotification){
}                      @objc            func            keyboardWillHide(notification: NSNotification){
}

Note: Don't forget to remove the keyboard notification observer in `viewWillDisappear`

                      override            func            viewWillDisappear(_            animated: Bool) {          NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardWillShowNotification, object:            nil)          NotificationCenter.default.removeObserver(self, name: UIResponder.keyboardWillHideNotification, object:            nil)          }

Step 6: Change the height on keyboard notification

While keyboard showing

                      @objc            func            keyboardWillShow(notification: NSNotification){                      guard            let            userInfo = notification.userInfo            else            {            return            }                      guard            let            keyboardSize = userInfo[UIResponder.keyboardFrameBeginUserInfoKey]            as? NSValue            else            {            return            }                      let            keybardFrame = keyboardSize.cgRectValue          textFieldHalfHeight =            self.view.frame.size.height - keybardFrame.height - 30          UIView.animate(withDuration: 0.2,          delay: 0.2,          options: UIView.AnimationOptions.curveEaseIn,          animations: {                      self.heightConstraint?.constant =            self.textFieldHalfHeight                      self.view.layoutIfNeeded()          },completion:            nil)          }

On keyboard hide

                      @objc            func            keyboardWillHide(notification: NSNotification){          UIView.animate(withDuration: 0.2, delay: 0.2, options: UIView.AnimationOptions.curveEaseIn, animations: {                      self.heightConstraint?.constant =            self.textFieldFullHeight                      self.view.layoutIfNeeded()          }, completion:            nil)          }