iOS Managing the Keyboard Using a Singleton + Delegate


Example

When I first started managing the keyboard I would use separate Notifications in each ViewController.

Notification Method (Using NSNotification):

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.keyboardNotification(_:)), name: UIKeyboardWillChangeFrameNotification, object: nil)
    }

    func keyboardNotification(notification: NSNotification) {
        guard let userInfo = notification.userInfo else { return }
    
        let endFrame = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.CGRectValue()
        let duration: NSTimeInterval = (userInfo[UIKeyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue ?? 0
        let animationCurveRawNSN = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? NSNumber
        let animationCurveRaw = animationCurveRawNSN?.unsignedLongValue ?? UIViewAnimationOptions.CurveEaseOut.rawValue
        let animationCurve: UIViewAnimationOptions = UIViewAnimationOptions(rawValue: animationCurveRaw)
    
        if endFrame?.origin.y >= UIScreen.mainScreen().bounds.size.height {
            lowerViewBottomConstraint.constant = 0
        } else {
            lowerViewBottomConstraint.constant = endFrame?.size.height ?? 0.0
        }
        view.animateConstraintWithDuration(duration, delay: NSTimeInterval(0), options: animationCurve, completion: nil)
    }
}

My problem was that I found myself writing this code again and again for every single ViewController. After experimenting a bit I found using a Singleton + Delegate pattern allowed me to reuse a bunch of code and organize all of the Keyboard Management in a single place!

Singleton + Delegate Method:

protocol KeyboardManagerDelegate: class {
    func keyboardWillChangeFrame(endFrame: CGRect?, duration: NSTimeInterval, animationCurve: UIViewAnimationOptions)
}

class KeyboardManager {

    weak var delegate: KeyboardManagerDelegate?

    class var sharedInstance: KeyboardManager {
        struct Singleton {
            static let instance = KeyboardManager()
        }
        return Singleton.instance
    }

    init() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(KeyboardManager.keyboardWillChangeFrameNotification(_:)), name: UIKeyboardWillChangeFrameNotification, object: nil)
    }

    @objc func keyboardWillChangeFrameNotification(notification: NSNotification) {
        guard let userInfo = notification.userInfo else { return }
    
        let endFrame = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.CGRectValue()
        let duration: NSTimeInterval = (userInfo[UIKeyboardAnimationDurationUserInfoKey] as? NSNumber)?.doubleValue ?? 0
        let animationCurveRawNSN = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? NSNumber
        let animationCurveRaw = animationCurveRawNSN?.unsignedLongValue ?? UIViewAnimationOptions.CurveEaseOut.rawValue
        let animationCurve: UIViewAnimationOptions = UIViewAnimationOptions(rawValue: animationCurveRaw)
    
        delegate?.keyboardWillChangeFrame(endFrame, duration: duration, animationCurve: animationCurve)
    }
}

Now when I want to manage the keyboard from a ViewController all I need to do is set the delegate to that ViewController and implement any delegate methods.

class ViewController: UIViewController {
    override func viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        KeyboardManager.sharedInstance.delegate = self
    }
}

// MARK: - Keyboard Manager

extension ViewController: KeyboardManagerDelegate {
    func keyboardWillChangeFrame(endFrame: CGRect?, duration: NSTimeInterval, animationCurve: UIViewAnimationOptions) {
        if endFrame?.origin.y >= UIScreen.mainScreen().bounds.size.height {
           lowerViewBottomConstraint.constant = 0
        } else {
            lowerViewBottomConstraint.constant = (endFrame?.size.height ?? 0.0)
        }
        view.animateConstraintWithDuration(duration, delay: NSTimeInterval(0), options: animationCurve, completion: nil)
    }
}

This method is very customizable too! Say we want to add functionality for UIKeyboardWillHideNotification. This is as easy as adding a method to our KeyboardManagerDelegate.

KeyboardManagerDelegate with UIKeyboardWillHideNotification:

protocol KeyboardManagerDelegate: class {
    func keyboardWillChangeFrame(endFrame: CGRect?, duration: NSTimeInterval, animationCurve: UIViewAnimationOptions)
    func keyboardWillHide(notificationUserInfo: [NSObject: AnyObject])
}

class KeyboardManager {
    init() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(KeyboardManager.keyboardWillChangeFrameNotification(_:)), name: UIKeyboardWillChangeFrameNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(KeyboardManager.keyboardWillHide(_:)), name: UIKeyboardWillHideNotification, object: nil)
    }

    func keyboardWillHide(notification: NSNotification) {
        guard let userInfo = notification.userInfo else { return }
        delegate?.keyboardWillHide(userInfo)
    }
}

Say we only want to implement func keyboardWillHide(notificationUserInfo: [NSObject: AnyObject]) in one ViewController. We can also make this method optional.

typealias KeyboardManagerDelegate = protocol<KeyboardManagerModel, KeyboardManagerConfigureable>

protocol KeyboardManagerModel: class {
    func keyboardWillChangeFrame(endFrame: CGRect?, duration: NSTimeInterval, animationCurve: UIViewAnimationOptions)
}

@objc protocol KeyboardManagerConfigureable {
    optional func keyboardWillHide(userInfo: [NSObject: AnyObject])
}

*Note this pattern helps avoid overuse of @objc. See http://www.jessesquires.com/avoiding-objc-in-swift/ for more details!

In summary, I've found using a Singleton + Delegate to manage the keyboard is both more efficient and easier to use than using Notifications