samples/RandomMusicPlayer/src/com/example/android/musicplayer/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.example.android.musicplayer;

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

/** 
 * 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 {
    AudioManager mAM;
    MusicFocusable mFocusable;

    public AudioFocusHelper(Context ctx, MusicFocusable focusable) {
        mAM = (AudioManager) ctx.getSystemService(Context.AUDIO_SERVICE);
        mFocusable = focusable;
    }

    /** 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);
    }

    /** 
     * 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:
                mFocusable.onGainedAudioFocus();
                break;
            case AudioManager.AUDIOFOCUS_LOSS:
            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
                mFocusable.onLostAudioFocus(false);
                break;
            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
                mFocusable.onLostAudioFocus(true);
                break;
             default:
        }
    }
}