There is no broadcast event for volume change.
However, there is an undocumented action called "android.media.VOLUME_CHANGED_ACTION
" which you could use, but it probably won't work on all devices/versions so it is not recommended.
Using other buttons (e.g. media buttons) would be possible though.
EDIT: Code sample (using the undocumented action):
AndroidManifest.xml
...
<receiver android:name="VolumeChangeReceiver" >
<intent-filter>
<action android:name="android.media.VOLUME_CHANGED_ACTION" />
</intent-filter>
</receiver>
...
VolumeChangeReceiver.java
public class VolumeChangeReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
if (intent.getAction().equals("android.media.VOLUME_CHANGED_ACTION")) {
int newVolume = intent.getIntExtra("android.media.EXTRA_VOLUME_STREAM_VALUE", 0);
int oldVolume = intent.getIntExtra("android.media.EXTRA_PREV_VOLUME_STREAM_VALUE", 0);
if (newVolume != oldVolume) {
Intent i = new Intent();
i.setClass(context, YourActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(i);
}
}
}
}
See this question if you want to unlock the screen when launching your app.