Comment animer ajouter UISearchBar sur le dessus de UINavigationBar

J'ai modifié de la Marque de répondre un peu à le faire fonctionner sous IOS 8 et swift.

class ViewController : UIViewController, UISearchBarDelegate {
var searchBar = UISearchBar()
var searchBarButtonItem: UIBarButtonItem?
var logoImageView   : UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
//Can replace logoImageView for titleLabel of navbar
let logoImage = UIImage(named: "logo-navbar")!
logoImageView = UIImageView(frame: CGRect(x: 0, y: 0, width: logoImage.size.width, height: logoImage.size.height))
logoImageView.image = logoImage
navigationItem.titleView = logoImageView
searchBar.delegate = self
searchBar.searchBarStyle = UISearchBarStyle.Minimal
searchBarButtonItem = navigationItem.rightBarButtonItem
}
@IBAction func searchButtonPressed(sender: AnyObject) {
showSearchBar()
}
func showSearchBar() {
searchBar.alpha = 0
navigationItem.titleView = searchBar
navigationItem.setLeftBarButtonItem(nil, animated: true)
UIView.animateWithDuration(0.5, animations: {
self.searchBar.alpha = 1
}, completion: { finished in
self.searchBar.becomeFirstResponder()
})
}
func hideSearchBar() {
navigationItem.setLeftBarButtonItem(searchBarButtonItem, animated: true)
logoImageView.alpha = 0
UIView.animateWithDuration(0.3, animations: {
self.navigationItem.titleView = self.logoImageView
self.logoImageView.alpha = 1
}, completion: { finished in
})
}
//MARK: UISearchBarDelegate
func searchBarCancelButtonClicked(searchBar: UISearchBar) {
hideSearchBar()
}
}

Following Nick's answer, I made a similar one on Xcode 7.1 -swift 2.0.
Note:
To the Navigation Bar, I added
(a) UIBarButtons( Drag& Drop) - menuButton & searchButton
(b) UIBarButtons (programatically) - leftSearchBarButtonItem & rightSearchBarButtonItem.
The common methods are : 
(a) showSearchBar(), hideSearchBar()
(b) revealToggle: - It is connected to SWRevealController for Slider Menu.

// DashBoardViewController.swift
import UIKit
class DashBoardViewController: UIViewController,UISearchBarDelegate,SWRevealViewControllerDelegate {
//MARK:- STORYBOARD REFERENCE
@IBOutlet weak var menuButton: UIBarButtonItem!
@IBOutlet weak var searchButtton: UIBarButtonItem!
//Making secondary Searchbar
var searchBar = UISearchBar()
var leftSearchBarButtonItem: UIBarButtonItem?
var rightSearchBarButtonItem: UIBarButtonItem?
var logoImageView   : UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
self.activateInitialUISetUp()
//   self.revealViewController().delegate = self
makeTopNavigationSearchbar()
}
override func viewWillAppear(animated: Bool) {
makeTopNavigationSearchbar()
activateInitialUISetUp()        
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
//MARK:- SEARCHBAR METHODS
func searchBarSearchButtonClicked(searchBar: UISearchBar) {
hideSearchBar()
searchBar.resignFirstResponder()
}
func searchBarTextDidBeginEditing(searchBar: UISearchBar) {
}
func searchBarCancelButtonClicked(searchBar: UISearchBar) {
hideSearchBar()
}
//Search Bar Appear & Disappear
func showSearchBar() {
searchBar.hidden =  false
searchBar.alpha = 0
navigationItem.titleView = searchBar
navigationItem.setLeftBarButtonItem(nil, animated: true)
navigationItem.setRightBarButtonItem(nil, animated: true)
UIView.animateWithDuration(0.5, animations: {
self.searchBar.alpha = 1
}, completion: { finished in
self.searchBar.becomeFirstResponder()
})
}
func hideSearchBar() {
hideSearchBarAndMakeUIChanges()
logoImageView.alpha = 0
UIView.animateWithDuration(0.3, animations: {
self.logoImageView.alpha = 1
}, completion: { finished in
})
}
//Making secondary Searchbar
func makeTopNavigationSearchbar()
{
let logoImage = UIImage(named: "password")!
logoImageView = UIImageView(frame: CGRect(x: 0, y: 0, width: logoImage.size.width, height: logoImage.size.height))
logoImageView.image = logoImage
searchButtton.customView?.addSubview(logoImageView)
searchBar.delegate = self
searchBar.searchBarStyle = UISearchBarStyle.Minimal
leftSearchBarButtonItem = navigationItem.leftBarButtonItem
rightSearchBarButtonItem =  navigationItem.rightBarButtonItem
leftSearchBarButtonItem?.tintColor =  UIColor.whiteColor()
rightSearchBarButtonItem?.tintColor =  UIColor.whiteColor()
}
//Adding secondary uibar butttons to navigation bar
func hideSearchBarAndMakeUIChanges ()
{
searchBar.hidden =  true
//Adding secondary uibarbuttons to the nav bar and revoke its methods
navigationItem.setLeftBarButtonItem(leftSearchBarButtonItem, animated: true)
navigationItem.setRightBarButtonItem(rightSearchBarButtonItem, animated: true)
leftSearchBarButtonItem?.title = "Menu"
leftSearchBarButtonItem?.target = self.revealViewController()
leftSearchBarButtonItem?.action = "revealToggle:"
rightSearchBarButtonItem?.title = "Search"
rightSearchBarButtonItem?.target = self
rightSearchBarButtonItem?.action = "showSearchBar"
//Adding Title Label
var navigationTitlelabel = UILabel(frame: CGRectMake(0, 0, 200, 21))
navigationTitlelabel.center = CGPointMake(160, 284)
navigationTitlelabel.textAlignment = NSTextAlignment.Center
navigationTitlelabel.textColor  = UIColor.whiteColor()
navigationTitlelabel.text = "WORK ORDER"
self.navigationController!.navigationBar.topItem!.titleView = navigationTitlelabel
}    
//UI-Related Methods
func activateInitialUISetUp()
{
self.navigationController?.navigationBarHidden =  false
self.navigationController?.navigationBar.barStyle = UIBarStyle.BlackOpaque
self.navigationController?.navigationBar.translucent =  true
self.navigationController?.navigationBar.backgroundColor =  UIColor.redColor()
//Nav Bar Searchbar
searchBar.delegate = self
searchBar.placeholder = "Start Your Search Here"
searchButtton.action = "showSearchBar"
searchButtton.target = self
//searchbar Text Color
var textFieldInsideSearchBar = searchBar.valueForKey("searchField") as? UITextField
textFieldInsideSearchBar?.textColor = UIColor.whiteColor()
//Nav Bar Title
self.title = "WORK ORDER"
if self.revealViewController() != nil {
menuButton.target = self.revealViewController()
menuButton.action = "revealToggle:"
self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
self.revealViewController().rearViewRevealWidth = self.view.frame.width / 2
self.revealViewController().rearViewRevealOverdraw = 0.0
self.view.addGestureRecognizer(self.revealViewController().tapGestureRecognizer())
}
}    
func revealController(revealController: SWRevealViewController!, didMoveToPosition position: FrontViewPosition) {
if(position.rawValue == 3)
{
}
else
{
}
print("position\(position)")
}    
}