Tab Bars
A tab bar appears at the bottom of an app screen and provides the ability to quickly switch between different sections of an app. Tab bars are translucent, may have a background tint, maintain the same height in all screen orientations, and are hidden when a keyboard is displayed. A tab bar may contain any number of tabs, but the number of visible tabs varies based on the device size and orientation. If some tabs can’t be displayed due to limited horizontal space, the final visible tab becomes a More tab, which reveals the additional tabs in a list on a separate screen.
In general, use a tab bar to organize information at the app level. A tab bar is a good way to flatten your information hierarchy and provide access to several peer information categories or modes at once.
Don’t remove or disable a tab when its function is unavailable. If tabs are available in some cases but not in others, your app’s interface becomes unstable and unpredictable. Ensure that all tabs are always enabled, and explain why a tab’s content is unavailable. For example, if there are no songs on an iOS device, the My Music tab in the Music app explains how to download songs.
Use a tab bar strictly for navigation. Tab bar buttons should not be used to perform actions. If you need to provide controls that act on elements in the current view, use a toolbar instead. See Toolbars.
Avoid having too many tabs. Each additional tab reduces the tappable area for selecting a tab and increases the complexity of your app, making it harder to locate information. Although a More tab can display extra tabs, this requires additional taps and is a poor use of space. Include essential tabs only, and use the minimum tabs necessary for your information hierarchy. Too few tabs can be a problem too, as it can make your interface feel disconnected. In general, use between three and five tabs on iPhone. A few more are acceptable on iPad.
Use badging to communicate unobtrusively. You can display a badge—a red oval containing white text and either a number or an exclamation point—on a tab to indicate that new information is associated with that view or mode.
Always switch contexts in the attached view. To keep your interface predictable, selecting a tab should always affect the view that’s directly attached to the tab bar, not another view elsewhere on screen. For example, selecting a tab on the left side of a split view shouldn’t cause the right side of the split view to suddenly change. Selecting a tab in a popover shouldn’t cause the view behind the popup to change.
For implementation details, see UITabBar.
Tip It’s important to understand the difference between a tab bar and a toolbar, because both types of bars appear at the bottom of an app screen. A tab bar lets the user switch quickly between different sections of an app, such as the Alarm, Stopwatch, and Timer tabs in the Clock app. A toolbar contains buttons for performing actions related to the current context, such as creating an item, deleting an item, adding an annotation, or taking a photo. See Toolbars. Tab bars and toolbars never appear together in the same view.