System UI is an Android application that enables display customization independent of third-party apps. In even simpler terms, everything you see on Android that is not an app is System UI.
How Does System UI Work?
Mobile device systems have changed dramatically over the years, but there remain two system giants: Android and iOS. Android is known for providing users with more options for customization through the System UI. In order for this system to work correctly with a wide range of apps, app developers must adhere to the basic requirements recommended and outlined by Google.
Years ago, Android introduced something called the System UI Tuner, which is a customization menu located with Android device settings. This tuner enables you to adjust the status and navigation bars on your device interface or make an app viewable on fullscreen. Through the System UI Tuner, you can enable night mode and dark theme, and turn icons on and off in the status.
Recently, Google determined that this tuner is better off hidden (rather than easily accessed through the Settings menu), but tech-savvy Android users can still activate the tuner through a specific set of commands.
Customizing Android’s System UI
For app developers, it is critical that System UI integrations are done correctly to ensure bugs are identified and eliminated before launching an app to users.
Customizing the Android System UI requires modification of source code, which can make future Android updates challenging. To work around this, Android came up with something called an overlay directory that overrides files and enables developers (or skilled users) to replace any resource files without modifying source code.
Another way of customizing the Android System UI is through customizing the user switcher, the lock screen and the first-time user setup. For instance, the user switcher can be customized through the Quick settings, the lock screen by the OEM, and the first-time user setup through an API.
Why go to so much effort to customize the UI? Well, customization delivers a better user experience, and the better the experience, the more satisfied the customer.