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Multitasking

Multitasking allows people to switch quickly among recently used apps.

image: ../Art/multitasking_2x.png

To support this experience, multitasking allows an app to enter a suspended state in the background when users switch away from it. When users switch back to the app, the app can resume quickly because it doesn’t have to reload its UI. People use the multitasking UI (shown above) to choose a recently used app.

Thriving in a multitasking environment hinges on achieving a harmonious coexistence with other apps on the device. At a high level, this means that all apps should:

  • Handle interruptions or audio from other apps gracefully

  • Stop and restart—that is, transition to and from the background—quickly and smoothly

  • Behave responsibly when not in the foreground

The following specific guidelines help your app succeed in the multitasking environment.

Be prepared for interruptions, and be ready to resume. Multitasking increases the probability that a background app will interrupt your app. Other features, such as the presence of ads and faster app-switching, can also cause more frequent interruptions. The more quickly and precisely you can save the current state of your app, the faster people can relaunch it and continue from where they left off. To give users a seamless restart experience, take advantage of UIKit’s state preservation and restoration functionality (for more information, see “State Preservation and Restoration”).

Make sure your UI can handle the double-high status bar. The double-high status bar appears during events such as in-progress phone calls, audio recording, and tethering. In unprepared apps the extra height of this bar can cause layout problems. For example, the UI can become pushed down or covered. In a multitasking environment, it’s especially important to be able to handle the double-high status bar properly because there are likely to be more apps that can cause it to appear.

Be ready to pause activities that require people’s attention or active participation. For example, if your app is a game or a media-viewing app, make sure your users don’t miss any content or events when they switch away from your app. When people switch back to a game or media viewer, they want to continue the experience as if they’d never left it.

Ensure that your audio behaves appropriately. Multitasking makes it more likely that other media activity is occurring while your app is running. It also makes it more likely that your audio will have to pause and resume to handle interruptions. For specific guidelines that help you make sure your audio meets people’s expectations and coexists properly with other audio on the device, see Sound.

Use local notifications sparingly. An app can arrange for local notifications to be sent at specific times, whether the app is suspended, running in the background, or not running at all. For the best user experience, avoid pestering people with too many notifications, and follow the guidelines for creating notification content described in Notification Center.

When appropriate, finish user-initiated tasks in the background. When people initiate a task, they usually expect it to finish even if they switch away from your app. If your app is in the middle of performing a user-initiated task that does not require additional user interaction, you should complete it in the background before suspending.