Android游戏之音频类设计

1、基础知识：

A. setVolumeControlStream(AudioManager.STREAM_MUSIC);
http://developer.android.com/training/managing-audio/volume-playback.html
http://developer.android.com/reference/android/app/Activity.html#setVolumeControlStream(int)

public final void  setVolumeControlStream (int streamType)
Added in API level 1

Suggests an audio stream whose volume should be changed by the hardware volume controls.
The suggested audio stream will be tied to the window of this Activity. Volume requests which are received while the Activity is in the

foreground will affect this stream.
It is not guaranteed that the hardware volume controls will always change this stream's volume (for example, if a call is in progress, its

stream's volume may be changed instead). To reset back to the default, use USE_DEFAULT_STREAM_TYPE.

Parameters

streamType
The type of the audio stream whose volume should be changed by the hardware volume controls. 

AudioManager的值：http://developer.android.com/reference/android/media/AudioManager.html
int STREAM_MUSIC The audio stream for music playback 

B.getAssets ()
http://developer.android.com/reference/android/content/res/Resources.html#getAssets()
public final AssetManager  getAssets ()
Added in API level 1

Retrieve underlying AssetManager storage for these resources.
C.AssetManager
http://developer.android.com/reference/android/content/res/AssetManager.html
D.AssetFileDescriptor
http://developer.android.com/reference/android/content/res/AssetFileDescriptor.html
E.SoundPool
http://developer.android.com/reference/android/media/SoundPool.html
The SoundPool class manages and plays audio resources for applications.
A SoundPool is a collection of samples that can be loaded into memory from a resource inside the APK or from a file in the file system. The

SoundPool library uses the MediaPlayer service to decode the audio into a raw 16-bit PCM mono or stereo stream. This allows applications to

ship with compressed streams without having to suffer the CPU load and latency of decompressing during playback.
http://developer.android.com/reference/android/media/SoundPool.html#SoundPool(int, int, int)
Parameters

maxStreams
the maximum number of simultaneous streams for this SoundPool object
streamType
the audio stream type as described in AudioManager For example, game applications will normally use STREAM_MUSIC.
srcQuality
the sample-rate converter quality. Currently has no effect. Use 0 for the default.

Returns
a SoundPool object, or null if creation failed
F.MediaPlayer
http://developer.android.com/reference/android/media/MediaPlayer.html
G.MediaPlayer.OnCompletionListener
http://developer.android.com/reference/android/media/MediaPlayer.OnCompletionListener.html

2、设计3个接口Sound，Music，Audio，音频Audio由声音Sound和音乐Music构成

package com.badlogic.androidgames.framework;

public interface Sound {
    public void play(float volume);

    public void dispose();
}

package com.badlogic.androidgames.framework;

public interface Music {
    public void play();

    public void stop();

    public void pause();

    public void setLooping(boolean looping);

    public void setVolume(float volume);

    public boolean isPlaying();

    public boolean isStopped();

    public boolean isLooping();

    public void dispose();
}

package com.badlogic.androidgames.framework;

public interface Audio {
    public Music newMusic(String filename);

    public Sound newSound(String filename);
}

3、针对3个接口实现每一个对应的类

package com.badlogic.androidgames.framework.impl;

import java.io.IOException;

import android.content.res.AssetFileDescriptor;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;

import com.badlogic.androidgames.framework.Music;

public class AndroidMusic implements Music, OnCompletionListener {
    MediaPlayer mediaPlayer;
    boolean isPrepared = false;

    public AndroidMusic(AssetFileDescriptor assetDescriptor) {
        mediaPlayer = new MediaPlayer();
        try {
            mediaPlayer.setDataSource(assetDescriptor.getFileDescriptor(),
                    assetDescriptor.getStartOffset(),
                    assetDescriptor.getLength());
            mediaPlayer.prepare();
            isPrepared = true;
            mediaPlayer.setOnCompletionListener(this);
        } catch (Exception e) {
            throw new RuntimeException("Couldn't load music");
        }
    }

    @Override
    public void dispose() {
        if (mediaPlayer.isPlaying())
            mediaPlayer.stop();
        mediaPlayer.release();
    }

    @Override
    public boolean isLooping() {
        return mediaPlayer.isLooping();
    }

    @Override
    public boolean isPlaying() {
        return mediaPlayer.isPlaying();
    }

    @Override
    public boolean isStopped() {
        return !isPrepared;
    }

    @Override
    public void pause() {
        if (mediaPlayer.isPlaying())
            mediaPlayer.pause();
    }

    @Override
    public void play() {
        if (mediaPlayer.isPlaying())
            return;

        try {
            synchronized (this) {
                if (!isPrepared)
                    mediaPlayer.prepare();
                mediaPlayer.start();
            }
        } catch (IllegalStateException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void setLooping(boolean isLooping) {
        mediaPlayer.setLooping(isLooping);
    }

    @Override
    public void setVolume(float volume) {
        mediaPlayer.setVolume(volume, volume);
    }

    @Override
    public void stop() {
        mediaPlayer.stop();
        synchronized (this) {
            isPrepared = false;
        }
    }

    @Override
    public void onCompletion(MediaPlayer arg0) {
        synchronized (this) {
            isPrepared = false;
        }
    }
}

package com.badlogic.androidgames.framework.impl;

import android.media.SoundPool;

import com.badlogic.androidgames.framework.Sound;

public class AndroidSound implements Sound {
    int soundId;
    SoundPool soundPool;
    
    public AndroidSound(SoundPool soundPool,int soundId) {
        this.soundId = soundId;
        this.soundPool = soundPool;
    }

    @Override
    public void play(float volume) {
        soundPool.play(soundId, volume, volume, 0, 0, 1);
    }

    @Override
    public void dispose() {
        soundPool.unload(soundId);
    }

}

package com.badlogic.androidgames.framework.impl;

import java.io.IOException;

import android.app.Activity;
import android.content.res.AssetFileDescriptor;
import android.content.res.AssetManager;
import android.media.AudioManager;
import android.media.SoundPool;

import com.badlogic.androidgames.framework.Audio;
import com.badlogic.androidgames.framework.Music;
import com.badlogic.androidgames.framework.Sound;

public class AndroidAudio implements Audio {
    AssetManager assets;
    SoundPool soundPool;

    public AndroidAudio(Activity activity) {
        activity.setVolumeControlStream(AudioManager.STREAM_MUSIC);
        this.assets = activity.getAssets();
        this.soundPool = new SoundPool(20, AudioManager.STREAM_MUSIC, 0);
    }

    @Override
    public Music newMusic(String filename) {
        try {
            AssetFileDescriptor assetDescriptor = assets.openFd(filename);
            return new AndroidMusic(assetDescriptor);
        } catch (IOException e) {
            throw new RuntimeException("Couldn't load music '" + filename + "'");
        }
    }

    @Override
    public Sound newSound(String filename) {
        try {
            AssetFileDescriptor assetDescriptor = assets.openFd(filename);
            int soundId = soundPool.load(assetDescriptor, 0);
            return new AndroidSound(soundPool, soundId);
        } catch (IOException e) {
            throw new RuntimeException("Couldn't load sound '" + filename + "'");
        }
    }   
}

本文浅述了“beginning-android-games”书本的相关基础知识和相关类的设计分析，
书本和源码：http://download.csdn.net/detail/yangzhenping/8420261
本篇中的类实现来自“beginning-android-games\ch07-gl-basics”