Understanding the Issue with Navigation Bar Items in iOS

In this article, we will delve into the world of navigation bars in iOS and explore why it seems like a simple task to add an image as a custom view for the left bar button item is not working as expected. We’ll go through the code, explore potential issues, and provide solutions to overcome these obstacles.

The Problem

The problem arises when trying to add a custom view, such as an UIImageView, as the left bar button item in a navigation controller’s navigation item. When we try to assign this custom view to the left bar button item programmatically, it seems like the image is only visible during the first run of the app.

For example, consider the following code snippet:

// In ViewControllerA
UIImageView *logoApp = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"logo.png"]];
[logoApp setFrame:CGRectMake(5, 5, 55, 30)];
UIBarButtonItem *containingLogoApp = [[UIBarButtonItem alloc] initWithCustomView:logoApp];
self.navigationItem.leftBarButtonItem = containingLogoApp;

// Later, in ViewControllerB
UIImageView *backImg = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"back.png"]];
[backImg setFrame:CGRectMake(5, 5, 17, 22)];
UIBarButtonItem *containingBackButton = [[UIBarButtonItem alloc]initWithCustomView:backImg];
self.navigationItem.leftBarButtonItem = containingBackButton;

In this code, we’re creating two custom UIImageView instances and trying to add them as the left bar button item in the navigation controller’s navigation item. However, when we run the app for the second time, the images don’t seem to appear.

The Solution

The solution lies in understanding how iOS handles navigation bars and the lifetime of navigation items.

In iOS, a navigation bar is essentially a container that holds various items such as the title, back button, and left bar button item. When you add a custom view to the left bar button item programmatically, it’s stored temporarily until the next time the app runs.

To make this work for all subsequent runs, we need to ensure that the custom view is preserved across sessions. This can be achieved by using a static property or instance variable to store the UIBarButtonItem instance and update its image every time it’s accessed.

Implementing the Solution

Let’s modify our previous code snippet to achieve this:

// In ViewControllerA
UIImageView *logoApp = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"logo.png"]];
[logoApp setFrame:CGRectMake(5, 5, 55, 30)];

UIButton *backButton = [UIButton buttonWithType:UIButtonTypeCustom];
[backButton setImage:[UIImage imageNamed:@"back.png"] forState:UIControlStateNormal];
[backButton addTarget:self action:@selector(backAction) forControlEvents:UIControlEventTouchUpInside];
[backButton setFrame:CGRectMake(0, 0, 50, 30)];

UIBarButtonItem *containingLogoApp = [[UIBarButtonItem alloc] initWithCustomView:logoApp];
self.navigationItem.leftBarButtonItem = containingLogoApp;

// Later, in ViewControllerB
[backButton setImage:[UIImage imageNamed:@"back.png"] forState:UIControlStateNormal];

[self.navigationItem setLeftBarButtonItem:[NSArray alloc] init]];
[self.navigationItem setLeftBarButtonItem:[[UIBarButtonItem alloc] initWithCustomView:backButton]];

As you can see, we’ve created a separate UIButton instance and stored its image in the imageNamed: method. Every time this button is accessed, we update its image to match the current image.

Conclusion

In this article, we explored the issue of adding an image as a custom view for the left bar button item in iOS navigation bars. We discovered that the problem lies in how iOS handles temporary storage of navigation items and presented a solution using static properties and instance variables to preserve our UIBarButtonItem instances.

By following these steps and implementing them into your project, you should be able to successfully add images as custom views for your left bar button item without any issues. Remember to update the image every time it’s accessed to ensure a smooth user experience.

Last modified on 2023-11-22