AudioFocusHelper.java

/*   
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.lq.util;

import android.content.Context;
import android.media.AudioManager;

import com.lq.service.MusicService;

/**
 * Convenience class to deal with audio focus. This class deals with everything
 * related to audio focus: it can request and abandon focus, and will intercept
 * focus change events and deliver them to a MusicFocusable interface (which, in
 * our case, is implemented by {@link MusicService}).
 * 
 * This class can only be used on SDK level 8 and above, since it uses API
 * features that are not available on previous SDK's.
 */
public class AudioFocusHelper implements
		AudioManager.OnAudioFocusChangeListener {
	/**
	 * Represents something that can react to audio focus events. We implement
	 * this instead of just using AudioManager.OnAudioFocusChangeListener
	 * because that interface is only available in SDK level 8 and above, and we
	 * want our application to work on previous SDKs.
	 */
	public interface MusicFocusable {
		/** Signals that audio focus was gained. */
		public void onGainedAudioFocus();

		/** Signals that audio focus was lost. */
		public void onLostAudioFocus();
	}

	AudioManager mAM;
	MusicFocusable mFocusable;

	// do we have audio focus?
	public static final int NoFocusNoDuck = 0; // we don't have audio focus, and
												// can't duck
	public static final int NoFocusCanDuck = 1; // we don't have focus, but can
												// play at a low volume
												// ("ducking")
	public static final int Focused = 2; // we have full audio focus

	private int mAudioFocus = NoFocusNoDuck;

	public AudioFocusHelper(Context ctx, MusicFocusable focusable) {
		if (android.os.Build.VERSION.SDK_INT >= 8) {
			mAM = (AudioManager) ctx.getSystemService(Context.AUDIO_SERVICE);
			mFocusable = focusable;
		} else {
			mAudioFocus = Focused; // no focus feature, so we always "have"
			// audio focus
		}
	}

	/** Requests audio focus. Returns whether request was successful or not. */
	public boolean requestFocus() {
		return AudioManager.AUDIOFOCUS_REQUEST_GRANTED == mAM
				.requestAudioFocus(this, AudioManager.STREAM_MUSIC,
						AudioManager.AUDIOFOCUS_GAIN);
	}

	/** Abandons audio focus. Returns whether request was successful or not. */
	public boolean abandonFocus() {
		return AudioManager.AUDIOFOCUS_REQUEST_GRANTED == mAM
				.abandonAudioFocus(this);
	}

	public void giveUpAudioFocus() {
		if (mAudioFocus == Focused && android.os.Build.VERSION.SDK_INT >= 8
				&& abandonFocus())
			mAudioFocus = NoFocusNoDuck;
	}

	public void tryToGetAudioFocus() {
		if (mAudioFocus != Focused && android.os.Build.VERSION.SDK_INT >= 8
				&& requestFocus())
			mAudioFocus = Focused;
	}

	/**
	 * Called by AudioManager on audio focus changes. We implement this by
	 * calling our MusicFocusable appropriately to relay the message.
	 */
	public void onAudioFocusChange(int focusChange) {
		if (mFocusable == null)
			return;
		switch (focusChange) {
		case AudioManager.AUDIOFOCUS_GAIN:
			mAudioFocus = Focused;
			mFocusable.onGainedAudioFocus();
			break;
		case AudioManager.AUDIOFOCUS_LOSS:
		case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
			mAudioFocus = NoFocusNoDuck;
			mFocusable.onLostAudioFocus();
			break;
		case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
			mAudioFocus = NoFocusCanDuck;
			mFocusable.onLostAudioFocus();
			break;
		default:
		}
	}

	public int getAudioFocus() {
		return mAudioFocus;
	}
}