Customizing UIBarButtonItem

As a developer, we often find ourselves working with user interface elements, such as buttons and navigation bars. In this article, we’ll dive into how to customize UIBarButtonItem in iOS.

Understanding NavigationItem

To begin, let’s understand the concept of navigationItem. This property is used by a view controller to update its visual state when a new view controller appears. It’s essential to grasp the difference between self.navigationController.navigationItem and simply self.navigationItem.

In Objective-C, every instance of a UIViewController has a navigationItem. However, this includes not only UINavigationController instances but also any other view controllers that have been added as children of a navigation controller.

The Issue with Self.navigationController.navigationItem

The issue arises when trying to modify self.navigationController.navigationItem. This property is used by a UINavigationController to update its visual state when a new view controller appears. However, you will rarely need to modify this property directly because the UINavigationController handles these updates internally.

When you try to set self.navigationController.navigationItem, you are essentially trying to modify what would be displayed if you had nested UINavigationControllers. In practice, this is not how navigation works in iOS.

The Correct Way to Customize UIBarButtonItem

To customize a UIBarButtonItem, you need to work with the view controller’s navigationItem property. This means that instead of accessing it through the navigation controller, you should access it directly on the root view controller.

For example, if your app uses a UINavigationController and a RootViewController that inherits from UIViewController, you would set the button’s style, target, and action using:

UIBarButtonItem *share = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"icon"] style:UIBarButtonItemStylePlain target:self action:@selector(share:)];
self.navigationItem.rightBarButtonItem = share;

This code sets the rightBarButtonItem of the RootViewController to an instance of UIBarButtonItem.

Understanding NavigationController

Now, let’s clarify what a navigationController is in this context. A UINavigationController is an instance of a view controller that contains one or more child view controllers. In our example, we create a navigation controller and add the RootViewController as its root view controller.

The navigationController property of a view controller is a reference to the navigation controller that the view controller represented by self is currently contained within.

For instance, if you have a view controller like this:

UIViewController* viewController = [[UIViewController alloc] initWithNibName:nil bundle:nil];
UINavigationController* navController = [[UINavigationController alloc] initWithRootViewController:viewController];

// This is TRUE: viewController.navigationController == navController

This code creates a navigation controller and adds the specified view controller as its root.

Example

To illustrate this concept, let’s consider an example. Suppose we have a RootViewController that contains a UINavigationController. We want to add a custom button to the navigation bar.

First, we create our UIBarButtonItem instance:

UIBarButtonItem *share = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"icon"] style:UIBarButtonItemStylePlain target:self action:@selector(share:)];

Next, we set this UIBarButtonItem as the right button item of the navigation controller’s root view controller (our RootViewController). However, we must access it through its navigationItem property:

self.navigationItem.rightBarButtonItem = share;

This sets the right button item of our RootViewController, which in turn displays this button on the navigation bar.

Conclusion

Customizing a UIBarButtonItem requires an understanding of iOS’s view controller hierarchy and how to work with the navigationItem property. By grasping these concepts, you can effectively add custom buttons to your app’s navigation bars.

Last modified on 2024-02-28