Cómo agregar múltiples UIBarButtonItems en el lado derecho de la barra de navegación?

-(void)viewDidLoad{

    UIBarButtonItem *anotherButton1 = [[UIBarButtonItem alloc] initWithTitle:@"Button_1" style:UIBarButtonItemStylePlain target:self action:@selector(button_1:)];

    UIBarButtonItem *anotherButton2 = [[UIBarButtonItem alloc] initWithTitle:@"Button_" style:UIBarButtonItemStylePlain target:self action:@selector(button_2:)];

    self.navigationItem.rightBarButtonItems=@[anotherButton1,anotherButton2];
}

Creo que nada de lo anterior va a funcionar

Prueba esto

var burgerItem = UIBarButtonItem(image: UIImage(named:"categories"), style: .Plain, target: self, action: "categories")
        var weatherItem = UIBarButtonItem(title: "Weather", style: .Plain, target: self, action: "weather")


        burgerItem.tintColor = UIColor.whiteColor()
        weatherItem.tintColor = UIColor.whiteColor()

        navigationItem.setRightBarButtonItems([burgerItem,weatherItem], animated: true)

Tienes que usar navigationItem.setRightBarButtonItems y ser cuidadoso. navigationItem tiene que ser de un controlador de vista.

class testViewController:UIViewController {

ovverride func viewDidLoad() {
    self.navigationItem.setRightBarButtonItems(...

}

}

Esto puede ser de ayuda para usted en objective-c ,

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {

    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.navigationItem.title = @"Title";
        UIBarButtonItem *logOutButton = [[UIBarButtonItem alloc] initWithTitle:@"Logout" style:UIBarButtonItemStylePlain target:self action:@selector(ButtonClickedAtIndex1:)];
        [logOutButton setTintColor:[UIColor blackColor]];
        logOutButton.tag = 1;

        UIBarButtonItem *syncBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Sync" style:UIBarButtonItemStylePlain target:self action:@selector(ButtonClickedAtIndex1:)];
        [syncBarButtonItem setTintColor:[UIColor blackColor]];
        syncBarButtonItem.tag = 2;

        self.navigationItem.leftBarButtonItem = logOutButton;
        self.navigationItem.rightBarButtonItem = syncBarButtonItem;

       float systemVersion = [[[UIDevice currentDevice] systemVersion] floatValue];

       if (systemVersion >= 7.0) {
           self.edgesForExtendedLayout = UIRectEdgeNone;
           self.navigationController.navigationBar.translucent = NO;
       }
    }
    return self;
}

En Swift 3 puedes usar:

let editImage   = UIImage(named: "plus")!
let searchImage = UIImage(named: "search")!

let editButton   = UIBarButtonItem(image: editImage,  style: .plain, target: self, action: #selector(didTapEditButton))
let searchButton = UIBarButtonItem(image: searchImage,  style: .plain, target: self, action: #selector(didTapSearchButton))

navigationItem.rightBarButtonItems = [editButton, searchButton]

Simplemente agregue este código:

self.navigationItem.leftBarButtonItem = nil

let button = UIButton(type: .custom)
button.setImage(UIImage (named: "ChatTab"), for: .normal)
button.frame = CGRect(x: 0.0, y: 0.0, width: 35.0, height: 35.0)
//button.addTarget(target, action: nil, for: .touchUpInside)
let barButtonItem = UIBarButtonItem(customView: button)

let button2 = UIButton(type: .custom)
button2.setImage(UIImage (named: "ActivityTab"), for: .normal)
button2.frame = CGRect(x: 0.0, y: 0.0, width: 35.0, height: 35.0)
//button.addTarget(target, action: nil, for: .touchUpInside)

let barButtonItem2 = UIBarButtonItem(customView: button2)
self.navigationItem.rightBarButtonItems = [barButtonItem, barButtonItem2]

Este es el resultado: