KeyboardNotificationHandler.swift

//
//  KeyboardHandler.swift
//
//  Helper protocol and extension to consolidate keyboard notification handling for
//  UIViewControllers.
//
//  Created by Edward Majcher on 6/21/16.
//

import UIKit

@objc
protocol KeyboardNotificationHandler {
    
    func keyboardWillShow(note: NSNotification)
    func keyboardWillHide(note: NSNotification)
    
}

extension KeyboardNotificationHandler where Self: UIViewController {
    
    func registerForKeyboardNotifications() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(Self.keyboardWillShow(_:)), name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(Self.keyboardWillHide(_:)), name: UIKeyboardWillHideNotification, object: nil)
    }
    
    func unregsiterForKeyboardNotifications() {
        NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().removeObserver(self, name: UIKeyboardWillHideNotification, object: nil)
    }
    
    func keyboardValues(fromNote note:NSNotification) -> (begin: CGRect, end: CGRect, duration: NSTimeInterval, curve: UIViewAnimationCurve)? {
        guard let userInfo = note.userInfo,
            begin = userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue,
            end = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue,
            duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? NSValue,
            curve = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? NSValue else {
                
            return nil
        }
        
        var animationDuration: NSTimeInterval = 0
        var animationCurve: UIViewAnimationCurve = .EaseIn
        
        duration.getValue(&animationDuration)
        curve.getValue(&animationCurve)

        return (begin.CGRectValue(), end.CGRectValue(), animationDuration, animationCurve)
    }
}