Automatically adjust scroll view according to keyboard visibility

AutoKeyboardAdjustmentProtocol.swift

//
//  AutoKeyboardAdjustmentProtocol.swift
//  Ducky Duke
//
//  Created by Doba Duc on 8/18/15.
//  Copyright (c) 2015 Doba Duc. All rights reserved.
//

import UIKit

public protocol AutoKeyboardAdjustmentProtocol {
    var scrollViewForKeyboardAdjustment: UIScrollView? { get }
    func contentInset(forKeyboardHeight keyboardHeight: CGFloat) -> UIEdgeInsets
    func adjustContent(keyboardHeight keyboardHeight: CGFloat)
}

extension UIViewController: AutoKeyboardAdjustmentProtocol {
    public var scrollViewForKeyboardAdjustment: UIScrollView? {
        return nil
    }
    // Call this to enable auto adjustment. E.g.: In `viewDidLoad()`
    public func enableKeyboardAutoHandling() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillHide:", name: UIKeyboardWillHideNotification, object: nil)
    }
    
    // Call this to enable auto adjustment. E.g.: In `deinit`
    public func disableKeyboardAutoHandling() {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    public func keyboardWillShow(notification: NSNotification) {
        if let keyboardSize = notification.userInfo?[UIKeyboardFrameEndUserInfoKey]!.CGRectValue {
            adjustContent(keyboardHeight: keyboardSize.height)
        }
    }

    public func keyboardWillHide(notification: NSNotification) {
        adjustContent(keyboardHeight: 0)
    }

    public func contentInset(forKeyboardHeight keyboardHeight: CGFloat) -> UIEdgeInsets {
        if let scrollView = scrollViewForKeyboardAdjustment {
            return UIEdgeInsets(top: scrollView.contentInset.top, left: scrollView.contentInset.left, bottom: keyboardHeight, right: scrollView.contentInset.right)
        } else {
            return UIEdgeInsetsZero
        }
    }

    public func adjustContent(keyboardHeight keyboardHeight: CGFloat) {
        guard let scrollView = scrollViewForKeyboardAdjustment else { return }

        UIView.animateWithDuration(0.3,
            delay: 0,
            options: .CurveEaseOut,
            animations: {
                scrollView.contentInset =  self.contentInset(forKeyboardHeight: keyboardHeight)
            },
            completion: nil)
    }
}