iphone - iOS use the volume buttons as input

Question

I've recently downloaded an app that uses the 'Volume -' button to toggle a value, and it uses the 'Volume +' button to start/stop recording of video. The app is called SloPro, and can be found in the app store. I thought it wasn't allowed to modify the behaviour of the iPhone's hardware. Any ideas on how this is done?

Answer 1

See the Audio Session Services References for more details, but basically you start an audio session with AudioSessionInitialize. Then you make it active with AudioSessionSetActive. Then listen for changes in the volume with AudioSessionAddPropertyListener where you can pass a callback that has type AudioSessionPropertyListener.

Check the following website out for an example: http://fredandrandall.com/blog/2011/11/18/taking-control-of-the-volume-buttons-on-ios-like-camera/