How do you start a background task in iOS?

What I am trying 开发者_JS百科to do is to let application run in the background when a user takes a specific action (pushes a button).

On blackberry, there is a method called application.requestbackgtound();

Is there something similar in iOS?

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If your app has requested background activity (via a UIBackgroundModes key for audio, voip, or location in the app's info.plist), or has requested extra background time for a limited period (via calling beginBackgroundTaskWithExpirationHandler:), then launching another app (such as Safari) via openURL: will put your app in the background.