How to animate add UISearchBar on top of UINavigationBar

If I set the displaysSearchBarInNavigationBar = YES in viewDidLoad, the search bar will be in navigation bar when the view show up. But I want to show search bar on top of navigation bar when I touch bar button item. It's like image below

normal navigation bar:

search bar on top of navigation bar after right bar button item clicked

I've modified Mark's answer a little to get it to work in IOS 8 and in 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()
  }
}

I think the basic idea would be to animate a fade-out of your existing navigation bar's items (leftBarButtonItem(s), titleView, rightBarButtonItem(s)), followed by an animated fade-in of your search bar after it is added as your navigationItem's title view. To revert, animate a fade-out of the search bar, followed by a replacement of your navigationBar's prior items.

The searchBar in the rough example below is stand-alone, but it could also come from elsewhere, like iOS8's new UISearchController. It also assumes that the view controller is embedded in a UINavigationController.

This example builds the UI programmatically, but you should be able to incorporate this approach with a Storyboard-built UI.

The animation that occurs when the user taps the "Cancel" button is a little rough, but hopefully might point the way to a smoother solution.

@interface ViewController() <UISearchBarDelegate>

@property (nonatomic, strong) UIButton *searchButton;
@property (nonatomic, strong) UIBarButtonItem *searchItem;
@property (nonatomic, strong) UISearchBar *searchBar;

@end

- (void)viewDidLoad {

    [super viewDidLoad];

    // create the magnifying glass button
    self.searchButton = [[UIButton alloc] init];
    // add button images, etc.
    [_searchButton addTarget:self action:@selector(searchButtonTapped:) forControlEvents:UIControlEventTouchUpInside];

    self.searchItem = [[UIBarButtonItem alloc] initWithCustomView:_searchButton];
    self.navigationItem.rightBarButtonItem = _searchItem;

    self.searchBar = [[UISearchBar alloc] init];
    _searchBar.showsCancelButton = YES;
    _searchBar.delegate = self;

}

- (void)searchButtonTapped:(id)sender {

  [UIView animateWithDuration:0.5 animations:^{
    _searchButton.alpha = 0.0f;

  } completion:^(BOOL finished) {

    // remove the search button
    self.navigationItem.rightBarButtonItem = nil;
    // add the search bar (which will start out hidden).
    self.navigationItem.titleView = _searchBar;
    _searchBar.alpha = 0.0;

    [UIView animateWithDuration:0.5
                     animations:^{
                       _searchBar.alpha = 1.0;
                     } completion:^(BOOL finished) {
                       [_searchBar becomeFirstResponder];
                     }];

  }];
}

#pragma mark UISearchBarDelegate methods
- (void)searchBarCancelButtonClicked:(UISearchBar *)searchBar {

  [UIView animateWithDuration:0.5f animations:^{
    _searchBar.alpha = 0.0;
  } completion:^(BOOL finished) {
    self.navigationItem.titleView = nil;
    self.navigationItem.rightBarButtonItem = _searchItem;
    _searchButton.alpha = 0.0;  // set this *after* adding it back
    [UIView animateWithDuration:0.5f animations:^ {
        _searchButton.alpha = 1.0;
    }];
  }];

}// called when cancel button pressed

I have just refactored Nick's answer to make it the POP way in Swift 4.

protocol SearchViewAnimateble : class{ }

extension SearchViewAnimateble where Self: UIViewController{

func showSearchBar(searchBar : UISearchBar) {
    searchBar.alpha = 0
    navigationItem.titleView = searchBar
    navigationItem.setRightBarButton(nil, animated: true)

    UIView.animate(withDuration: 0.5, animations: {
        searchBar.alpha = 1
    }, completion: { finished in
        searchBar.becomeFirstResponder()
    })
}

func hideSearchBar( searchBarButtonItem : UIBarButtonItem, titleView : UIView) {
    navigationItem.setRightBarButton(searchBarButtonItem, animated: true)

    titleView.alpha = 0

    UIView.animate(withDuration: 0.3, animations: {
        self.navigationItem.titleView = titleView
        titleView.alpha = 1

    }, completion: { finished in

    })
 }
}

Then you can use it like this

class ViewController : UIViewController, UISearchBarDelegate, SearchViewAnimateble {
 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 = .minimal
    searchBar.showsCancelButton = true

    searchBarButtonItem = navigationItem.rightBarButtonItem
 }

 @IBAction func searchButtonPressed(sender: AnyObject) {
    showSearchBar(searchBar: searchBar)
 }



 //MARK: UISearchBarDelegate
 func searchBarCancelButtonClicked(searchBar: UISearchBar) {

    hideSearchBar( searchBarButtonItem : searchBarButton!, titleView : logoImageView)
  }
}

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)")

    }    
}