KeyboardViewController.swift

//
//  ViewController.swift
//  KeyboardTest
//
//  Created by Adam Śliwakowski on 01.12.2015.
//  Copyright © 2015 Adam Śliwakowski. All rights reserved.
//

import UIKit
typealias AnimationClosure = (() -> Void)

class ViewController: UIViewController {
    
    @IBOutlet weak var constraintYCenter: NSLayoutConstraint!
    @IBOutlet weak var textField: UITextField!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupKeyboardNotifcationListeners()
    }
    
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        textField.becomeFirstResponder()
    }
    
    override func keyboardWillShowAnimation() -> AnimationClosure {
        return {
            self.constraintYCenter.constant = 100
            self.view.layoutIfNeeded()
        }
    }
    
    override func keyboardWillHideAnimation() -> AnimationClosure {
        return { }
    }
    
    deinit {
        removeKeyboardNotificationListeners()
    }
}

extension UIViewController {
    var notifications: [(key: String, sel: String)] {
        return [
            (UIKeyboardWillShowNotification, "keyboardWillShow:"),
            (UIKeyboardWillHideNotification, "keyboardWillHide:")
        ]
    }
    
    var notificationCenter: NSNotificationCenter {
        return NSNotificationCenter.defaultCenter()
    }
    
    func keyboardWillShowAnimation() -> AnimationClosure {
        assertionFailure("this needs to be overriden")
        return { }
    }
    
    func keyboardWillHideAnimation() -> AnimationClosure {
        assertionFailure("this needs to be overriden")
        return { }
    }
    
    func setupKeyboardNotifcationListeners() {
        notifications.forEach { notificationCenter.addObserver(self, selector: Selector($0.sel), name: $0.key, object: nil) }
    }
    
    func removeKeyboardNotificationListeners() {
        notifications.forEach { notificationCenter.removeObserver(self, name: $0.key, object: nil) }
    }
    
    func keyboardWillShow(notification: NSNotification) {
        animate(keyboardWillShowAnimation(), notification: notification)
    }
    
    func keyboardWillHide(notification: NSNotification) {
        animate(keyboardWillHideAnimation(), notification: notification)
    }
    
    func animate(animation: AnimationClosure, notification: NSNotification) {
        let userInfo = notification.userInfo as! Dictionary<String, AnyObject>
        let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSTimeInterval
        let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey]!.intValue
        let curveAnimationOption = UIViewAnimationOptions(rawValue: UInt(animationCurve))
        let options: UIViewAnimationOptions = [.BeginFromCurrentState, curveAnimationOption]
        
        UIView.animateWithDuration(animationDuration, delay: 0, options: options, animations: animation, completion: nil)
    }
}