com.codename1.background

Interface BackgroundFetch

public interface BackgroundFetch

An interface that can be implemented by an app's main class to support background fetch.

What is Background Fetch?

Background fetch is a mechanism whereby an application is granted permission by the operating system to update its data periodically. At times of the native platform's choosing, an app that supports background fetch will be started up (in the background), and its performBackgroundFetch(long, com.codename1.util.Callback) method will be called.

Note: Since the app will be launched directly to the background, you cannot assume that the start() method has been run prior to the performBackgroundFetch(long, com.codename1.util.Callback) method being called.

How to Implement Background Fetch

Apps that wish to implement background fetch must implement the BackgroundFetch interface in their main class. On iOS, you also need to include fetch in the list of background modes (i.e. include "fetch" in the ios.background_modes build hint.)

In addition to implementing the BackgroundFetch interface, apps must explicitly set the background fetch interval calling Display.setPreferredBackgroundFetchInterval(int) at some point, usually in the start() or init() method.

Platform Support

Currently background fetch is supported on iOS, Android, and in the Simulator (simulated using timers when the app is paused). You should use the Display.isBackgroundFetchSupported() method to find out if the current platform supports it.

Examples

Method Summary

Modifier and Type	Method and Description
void	performBackgroundFetch(long deadline, Callback<Boolean> onComplete) A callback that may be periodically called by the platform to allow the app to fetch data in the background.

Method Detail

performBackgroundFetch

void performBackgroundFetch(long deadline,
                            Callback<Boolean> onComplete)

A callback that may be periodically called by the platform to allow the app to fetch data in the background.

Parameters:

deadline - The deadline (milliseconds since epoch) by which the fetch should be completed. If not completed by this time, the app may be killed by the OS. On iOS, there is a limit of 30 seconds to perform background fetches.

onComplete - Callback that MUST be called when the fetch is complete. If it is not called, some platforms (e.g. iOS) may refuse to allow the app to perform background fetches in the future.

See Also:

com.codename1.ui.Display.setPreferredBackgroundFetchInterval(int), com.codename1.ui.Display.getPreferredBackgroundFetchInterval(), com.codename1.ui.Display.isBackgroundFetchSupported()