Android devices also include a persistent status bar, providing access to notifications and information about the local time, signal strength, battery level, and more. Android will account for the software navigation bar (if present) as well as the status bar, automatically reserving that space and reducing the portion of the screen available to your app. For example, on a Nexus 5, while the screen is 360x640dp, the navigation bar in portrait mode is 48dp tall and the status bar is 24dp tall, so your app has 360x568dp space to present content. While you can hide the status bar (and even the navigation bar in limited situations), it’s best to leave the system UI present and allow users immediate access to those system functions. Android 4.4 and 5.0 introduced new features allowing you to draw behind the system UI to present your app content more immersively. Finally, you’re guaranteed to have hardware volume keys, so in most cases, you won’t need to include volume controls in your software UI.

The system Back button

The system Back button will be always available on every Android device, either as a physical button or on the screen in the system navigation bar. As a designer, you rarely have to define functionality for the Back button. You normally don’t need to customize Android’s automatic Back button behavior. By default, pressing Back closes the current screen and takes you to the previous screen, even if it was a part of another app (e.g. if another app opened your photo editing app using intents). If you’re at the first screen in your app, pressing Back takes you to the user’s home screen. Pressing Back from the home screen doesn’t take you any further back. Note that the Back button is distinct from the Up icon that appears in your app in detail screens. While Back navigates users temporally, Up navigates up the app’s hierarchical structure, and should never kick the user out of the app, even if you entered from a different app. Keep in mind that the text to the right of the Up button isn’t related to the button like it is on iOS. If that text is present, it should represent a title for the current screen.

Bottom tabs

On iOS, it’s common to use a bottom tab bar to switch between views in the app. The bottom navigation material design pattern includes best practices for adopting this navigation structure on Android, including implications for the Back button, scrolling and swiping behavior, and visual styling.

It’s also common on Android to use a tab bar at the top of the screen. A top tab bar is preferable in a number of situations: