Scrolling the view if the keyboard is covering it.

//
//  SignUpViewController.swift
//  Culpability
//
//  Created by Lazar Nikolov on 2/26/16.
//  Copyright © 2016 Lazar Nikolov. All rights reserved.
//

import UIKit

class SignUpViewController: UIViewController {

    @IBOutlet weak var tfUsername: UITextField!
    @IBOutlet weak var tfPassword: UITextField!
    @IBOutlet weak var tfConfirmPassword: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

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

    }

    func keyboardWillShow(notification: NSNotification) {
        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {
            if self.tfUsername.isFirstResponder() {
                let usernameBottomY = self.tfUsername.frame.origin.y + self.tfUsername.frame.height

                if usernameBottomY <= self.view.frame.height && usernameBottomY >= (self.view.frame.height - keyboardSize.height) {
                    // Scroll it
                    let verticalDifference = usernameBottomY - (self.view.frame.height - keyboardSize.height)
                    UIView.animateWithDuration(0.3, animations: {
                        self.view.frame.origin.y -= verticalDifference
                    })
                }
            } else if self.tfPassword.isFirstResponder() {
                let passwordBottomY = self.tfPassword.frame.origin.y + self.tfPassword.frame.height

                if passwordBottomY <= self.view.frame.height && passwordBottomY >= (self.view.frame.height - keyboardSize.height) {
                    // Scroll it
                    let verticalDifference = passwordBottomY - (self.view.frame.height - keyboardSize.height)
                    UIView.animateWithDuration(0.3, animations: {
                        self.view.frame.origin.y -= verticalDifference
                    })
                }
            } else if self.tfConfirmPassword.isFirstResponder() {
                let confirmPasswordBottomY = self.tfConfirmPassword.frame.origin.y + self.tfConfirmPassword.frame.height

                if confirmPasswordBottomY <= self.view.frame.height && confirmPasswordBottomY >= (self.view.frame.height - keyboardSize.height) {
                    // Scroll it
                    let verticalDifference = confirmPasswordBottomY - (self.view.frame.height - keyboardSize.height)
                    UIView.animateWithDuration(0.3, animations: {
                        self.view.frame.origin.y -= verticalDifference
                    })
                }
            }
        }
    }

    func keyboardWillHide(notification: NSNotification) {
        if self.view.frame.origin.y < 0 {
            UIView.animateWithDuration(0.3, animations: {
                self.view.frame.origin.y = 0
            })
        }
    }
}