Registering for Keyboard Events

Basic Use Case

Often, you will have to rearrange views when the keyboard is shown or hidden to ensure that the appropriate views and controls are visible while the user is typing. To achieve this, we will register for the keyboard events which are fired when the keyboard is shown or hidden.

This mechanism is called NSNotifications. It is commonly used for system events like keyboard, device rotation, and coming back from or going into standby. For example, when coming back from standby, it's common to refresh the network data of the view controller.

Step 1: Defining the method to be called

In your view controller, define 2 methods that you want to be called when the keyboard is shown or hidden.

func keyboardWillShow(notification: NSNotification!) {
        
}

func keyboardWillHide(notification: NSNotification!) {
        
}

You can put the methods above anywhere in the view controller file.

Step 2: Register for the keyboard events

In the init or viewDidLoad methods, register for keyboard events and tie them to the methods you defined in Step 1.

NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillHide:", name: UIKeyboardWillHideNotification, object: nil)

Note: You must place a colon in selector names for functions with a parameter, i.e "keyboardWillShow:"

Step 3: Add a UITextField to the view

Place a UITextField within the view using Interface Builder. Then, use the Assistant Editor button to reveal the associated ViewController code. Ctrl+click on the text field and drag the blue line to the ViewController in order to create either an Outlet or Action Handler for the text field. We will select Outlet and name the outlet according to the purpose of the UITextField.

Step 4: Offset the UITextField when the keyboard is shown

Near the top of the ViewController, where you create outlets, define variables for the initial y position of the text field and the offset amount.

var initialY: CGFloat!
let offset: CGFloat = -50

Next, within the viewDidLoad method record the initial y position of the text field.

initialY = username.frame.origin.y

Finally, within the keyboardWillShow method, update the y position of the text field to the, "keyboard shown" position.

username.frame.origin.y = initialY + offset)

Note: If your keyboard does not show when you click within the text field. Make sure that you have the external keyboard simulation disabled. Go to menu Hardware | Keyboard and make sure "Connect Hardware Keyboard" is unchecked.

Step 5: Move UITextField back when keyboard is hidden

Now we will simply move the UITextField back to its original y position when the keyboard is hidden. This will occur within the keyboardWillHide method.

username.frame.origin.y = initialY 

Step 6: Hide the Keyboard When Tapping Outside the TextField

If you run the simulator now, you notice that when you click on the text field it will animate up as it should, but when you click away you cannot hide the keyboard. So we need to have the keyboard hide event triggered. A common way to do this is to tap away from the text field trigger a keyboard hide.

• Drag and drop a UITapGesture recognizer from the Object Library to the background view.
• Ctrl+click and drag from the Tap Gesture Recognizer to the View Controller shown in the assistant editor. We will select the Action option and name the handler didTap.
• Within the didTap method we simply have the line

view.endEditing(true)

This will trigger the keyboardWillHide method on our view controller.