In iOS 11, developers began to notice an issue with the navigation bar's `rightBarButtonItem` when using an image-button. While navigation bars are a fundamental part of many iOS applications, the introduction of iOS 11 brought peculiar challenges for those leveraging image-buttons as navigation items. This issue could significantly impact the user interface's consistency and usability, making it crucial for developers to understand the intricacies and potential workarounds.

Understanding the Issue

Context

The navigation bar often serves as a critical UI component in iOS apps, typically housing elements like a back button, title, and optional items (such as edit or add buttons) located on the right. When these right bar button items are set using an `UIImage`, developers noted inconsistencies in button placement and scaling with the arrival of iOS 11.

Problem Description

The `rightBarButtonItem` image-button bug primarily manifested in two forms:

1. Image Scaling: Images failed to scale correctly, either occupying too much space or being cropped.
2. Alignment Issues: The button's position would appear unexpectedly, either too far to the right or slightly misaligned vertically.

Both issues can degrade the intended design aesthetic of the app and hinder usability, particularly on different screen sizes or device orientations.

Technical Explanation

Navigation Bar in iOS

A `UINavigationBar` in iOS typically consists of several elements, including `UINavigationItem`. The `UINavigationItem` holds various properties like `title`, `leftBarButtonItem`, and `rightBarButtonItem`. These right bar button items can be set as custom `UIBarButtonItems`, with the option to use `UIImage` objects instead of text for aesthetic purposes.

Rendering Changes in iOS 11

With iOS 11, Apple introduced several changes to the rendering mechanisms of navigation bars. Dynamic Type and adaptive layouts were emphasized, potentially affecting the way images were rendered and aligned. Changes in layout margins and safe areas also played a role in how components were positioned relative to the screen's edges.

Code Example

Here's a typical scenario where a developer might encounter this issue: