Swift - Add same navigation bar items to every page

Question

I am trying to add the same navigation bar items to every tab in my application. I currently have them set up correctly in my homeController, but I want to move the code to a separate file and remotely implement it wherever I want.

For example: adding a [search] icon to the left side of the navigation bar without having to use the same code in every swift file.

I don't know whether I should create an enum, protocol or class. What is the best way to do this?

let menuButton = UIButton(type: UIButtonType.system)
menuButton.frame = CGRect(x: 0, y: 0, width: 20, height: 20)
menuButton.addTarget(self, action: #selector(openSearch), for: .touchUpInside)
menuButton.setImage(UIImage(named: "icon_search"), for: UIControlState())
let menuBarButtonItem = UIBarButtonItem(customView: menuButton)

navigationItem.leftBarButtonItems = [menuBarButtonItem]

func openSearch() {
 // Some code
}

Answer 1

My recommended approach to this would be to create a base view controller class and make all your individual view controllers inheirit from this rather than directly from UIViewController.

Whilst you could do a quick and dirty extension as Umair suggests, this isn't practical for other applications whereas a base view controller allows you to basically add functionality/customise appearance of any aspect of all view controllers within your app.

Here is some example code:

class BaseViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        let menuButton = UIButton(type: UIButtonType.system)
        menuButton.frame = CGRect(x: 0, y: 0, width: 20, height: 20)
        menuButton.addTarget(self, action: #selector(openSearch), for:    .touchUpInside)
        menuButton.setImage(UIImage(named: "icon_search"), for: UIControlState())
        let menuBarButtonItem = UIBarButtonItem(customView: menuButton)

        navigationItem.leftBarButtonItems = [menuBarButtonItem
    }

    func openSearch() {

    }
}

Then for all view controllers in your app, just make the declaration:

class SomeRandomViewController: BaseViewController { }

EDIT:

As correctly pointed out in the comments, you will have to do this in every base class. (UIViewController, UITableViewController, UITabViewController etc...) There is a way around this but it is often considered one of the dark arts of the Objective-C runtime. I am of course talking about method swizzling. The following code essentially swaps the implemetations of UIViewController's viewWillAppear: and a custom method. It is totally safe if done correctly, and a correct implementation is shown below.

extension UIViewController {
    public override class func initialize() {
        struct Static {
            static var token: dispatch_once_t = 0
        }

        // make sure this isn't a subclass
        if self !== UIViewController.self {
            return
        }

        dispatch_once(&Static.token) {
            let originalSelector = Selector("viewWillAppear:")
            let swizzledSelector = Selector("extended_viewWillAppear:")

            let originalMethod = class_getInstanceMethod(self, originalSelector)
            let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)

            let didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

            if didAddMethod {
                class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
            } else {
                method_exchangeImplementations(originalMethod, swizzledMethod)
            }
        }
    }

    // MARK: - Method Swizzling

    func extended_viewWillAppear(animated: Bool) {
        self.extended_viewWillAppear(animated)

        // Call your code here that you want to run for all view controllers, table view controllers, tab view controllers etc...
    }
}

Some developers can't stand the above concept, and you should be aware that it could potentially change in a future release of iOS and break. That said, it won't get your app rejected as it is an actual programming technique.