android系统按键音framework流程源码详细解析

private void setSoundEffectsEnabled(boolean enabled) {
            mAudioManager = (AudioManager) getActivity().getSystemService(Context.AUDIO_SERVICE); //1
        if (enabled) {
            mAudioManager.loadSoundEffects();   // 从这里可以看到调用AudioManager里面的方法打开按键音
        } else {
            mAudioManager.unloadSoundEffects();
        }
        Settings.System.putInt(getActivity().getContentResolver(),
                Settings.System.SOUND_EFFECTS_ENABLED, enabled ? 1 : 0);
    }

@Override
    public Object getSystemService(@ServiceName @NonNull String name) {
        if (getBaseContext() == null) {
            throw new IllegalStateException(
                    "System services not available to Activities before onCreate()");
        }
        if (WINDOW_SERVICE.equals(name)) {
            return mWindowManager;
        } else if (SEARCH_SERVICE.equals(name)) {
            ensureSearchManager();
            return mSearchManager;
        }
        return super.getSystemService(name);    //除了WINDOW_SERVICE和SEARCH_SERVICE外，其他服务都在父类中
    }

@Override
    public Object getSystemService(String name) {
        if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            if (mInflater == null) {
                mInflater = LayoutInflater.from(getBaseContext()).cloneInContext(this);
            }
            return mInflater;
            
        }
        return getBaseContext().getSystemService(name);  //还要再往上
    }

@SuppressWarnings("unchecked")
    public final @Nullable <T> T getSystemService(@NonNull Class<T> serviceClass) {
        // Because subclasses may override getSystemService(String) we cannot
        // perform a lookup by class alone.  We must first map the class to its
        // service name then invoke the string-based method.
        String serviceName = getSystemServiceName(serviceClass);
        return serviceName != null ? (T)getSystemService(serviceName) : null;
    }
/**
     * Gets the name of the system-level service that is represented by the specified class.
     *
     * @param serviceClass The class of the desired service.
     * @return The service name or null if the class is not a supported system service.
     */
    public abstract @Nullable String getSystemServiceName(@NonNull Class<?> serviceClass);

    /**
     * Use with {@link #getSystemService(String)} to retrieve a
     * {@link android.os.PowerManager} for controlling power management,
     * including "wake locks," which let you keep the device on while
     * you're running long tasks.
     */
    public static final String POWER_SERVICE = "power";

   /**
     * Use with {@link #getSystemService(String)} to retrieve a
     * {@link android.view.WindowManager} for accessing the system's window
     * manager.
     *
     * @see #getSystemService(String)
     * @see android.view.WindowManager
     */
    public static final String WINDOW_SERVICE = "window";

    /**
     * Use with {@link #getSystemService(String)} to retrieve a {@link
     * android.net.wifi.WifiManager} for handling management of
     * Wi-Fi access.
     *
     * @see #getSystemService(String)
     * @see android.net.wifi.WifiManager
     */
    public static final String WIFI_SERVICE = "wifi";

    /**
     * Use with {@link #getSystemService(String)} to retrieve a
     * {@link android.media.AudioManager} for handling management of volume,
     * ringer modes and audio routing.
     *
     * @see #getSystemService(String)
     * @see android.media.AudioManager    //在audiomanager 里面
     */
    public static final String AUDIO_SERVICE = "audio";

framework/base/media/java/android/media/AudioManager.java
**
 * AudioManager provides access to volume and ringer mode control.
 */
@SystemService(Context.AUDIO_SERVICE)  //通过注解来讲AUDIO_SERVICE与AudioManager绑定在一块
public class AudioManager {

    private Context mOriginalContext;
    private Context mApplicationContext;
    private long mVolumeKeyUpTime;

/**
     *  Load Sound effects.
     *  This method must be called when sound effects are enabled.
*/
    public void loadSoundEffects() {
        final IAudioService service = getService();
        try {
            service.loadSoundEffects();
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

private static IAudioService getService()
{
    if (sService != null) {
        return sService;
    }
    IBinder b = ServiceManager.getService(Context.AUDIO_SERVICE);
    sService = IAudioService.Stub.asInterface(b);
    return sService;
}

/**
     * Returns a reference to a service with the given name
     * @param name the name of the service to get
     * @return a reference to the service, or <code>null</code> if the service doesn't exist
*/
    public static IBinder getService(String name) {
        try {
            IBinder service = sCache.get(name);   //在这个里面拿到
            if (service != null) {
                return service;
            } else {
                return Binder.allowBlocking(rawGetService(name));
            }
        } catch (RemoteException e) {
            Log.e(TAG, "error in getService", e);
        }
        return null;
    }

/**
     * Cache for the "well known" services, such as WM and AM.
*/
    private static HashMap<String, IBinder> sCache = new HashMap<String, IBinder>();

    /**
     * This is only intended to be called when the process is first being brought
     * up and bound by the activity manager. There is only one thread in the process
     * at that time, so no locking is done.
     *
     * @param cache the cache of service references
     * @hide
     */
    public static void initServiceCache(Map<String, IBinder> cache) {
        if (sCache.size() != 0) {
            throw new IllegalStateException("setServiceCache may only be called once");
        }
        sCache.putAll(cache);
    }

/**
     * Loads samples into the soundpool.
     * This method must be called at first when sound effects are enabled
     */
    public boolean loadSoundEffects() {
        int attempts = 3;
        LoadSoundEffectReply reply = new LoadSoundEffectReply();

        synchronized (reply) {
            sendMsg(mAudioHandler, MSG_LOAD_SOUND_EFFECTS, SENDMSG_QUEUE, 0, 0, reply, 0); //发送消息
            while ((reply.mStatus == 1) && (attempts-- > 0)) {
                try {
                    reply.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
                } catch (InterruptedException e) {
                    Log.w(TAG, "loadSoundEffects Interrupted while waiting sound pool loaded.");
                }
            }
        }
        return (reply.mStatus == 0);
    }

case MSG_LOAD_SOUND_EFFECTS:
                    //FIXME: onLoadSoundEffects() should be executed in a separate thread as it
                    // can take several dozens of milliseconds to complete
                    boolean loaded = onLoadSoundEffects();   // 调用这个方法
                    if (msg.obj != null) {
                        LoadSoundEffectReply reply = (LoadSoundEffectReply)msg.obj;
                        synchronized (reply) {
                            reply.mStatus = loaded ? 0 : -1;
                            reply.notify();
                        }
                    }
                    break;

private boolean onLoadSoundEffects() {
            int status;

            synchronized (mSoundEffectsLock) {
                if (!mSystemReady) {
                    Log.w(TAG, "onLoadSoundEffects() called before boot complete");
                    return false;
                }

                if (mSoundPool != null) {
                    return true;
                }

                loadTouchSoundAssets();     // 记载要播放声音的资源

                mSoundPool = new SoundPool.Builder()
                        .setMaxStreams(NUM_SOUNDPOOL_CHANNELS)
                        .setAudioAttributes(new AudioAttributes.Builder()
                            .setUsage(AudioAttributes.USAGE_ASSISTANCE_SONIFICATION)
                            .setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)
                            .build())
                        .build();    //链式调用
                mSoundPoolCallBack = null;
                mSoundPoolListenerThread = new SoundPoolListenerThread();
                mSoundPoolListenerThread.start();
                int attempts = 3;
                while ((mSoundPoolCallBack == null) && (attempts-- > 0)) {
                    try {
                        // Wait for mSoundPoolCallBack to be set by the other thread
                        mSoundEffectsLock.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
                    } catch (InterruptedException e) {
                        Log.w(TAG, "Interrupted while waiting sound pool listener thread.");
                    }
                }

                if (mSoundPoolCallBack == null) {
                    Log.w(TAG, "onLoadSoundEffects() SoundPool listener or thread creation error");
                    if (mSoundPoolLooper != null) {
                        mSoundPoolLooper.quit();
                        mSoundPoolLooper = null;
                    }
                    mSoundPoolListenerThread = null;
                    mSoundPool.release();
                    mSoundPool = null;
                    return false;
                }
                /*
                 * poolId table: The value -1 in this table indicates that corresponding
                 * file (same index in SOUND_EFFECT_FILES[] has not been loaded.
                 * Once loaded, the value in poolId is the sample ID and the same
                 * sample can be reused for another effect using the same file.
                 */
                int[] poolId = new int[SOUND_EFFECT_FILES.size()];
                for (int fileIdx = 0; fileIdx < SOUND_EFFECT_FILES.size(); fileIdx++) {
                    poolId[fileIdx] = -1;
                }
                /*
                 * Effects whose value in SOUND_EFFECT_FILES_MAP[effect][1] is -1 must be loaded.
                 * If load succeeds, value in SOUND_EFFECT_FILES_MAP[effect][1] is > 0:
                 * this indicates we have a valid sample loaded for this effect.
                 */

                int numSamples = 0;
                for (int effect = 0; effect < AudioManager.NUM_SOUND_EFFECTS; effect++) {
                    // Do not load sample if this effect uses the MediaPlayer
                    if (SOUND_EFFECT_FILES_MAP[effect][1] == 0) {
                        continue;
                    }
                    if (poolId[SOUND_EFFECT_FILES_MAP[effect][0]] == -1) {
                        String filePath = getSoundEffectFilePath(effect);
                        int sampleId = mSoundPool.load(filePath, 0);
                        if (sampleId <= 0) {
                            Log.w(TAG, "Soundpool could not load file: "+filePath);
                        } else {
                            SOUND_EFFECT_FILES_MAP[effect][1] = sampleId;
                            poolId[SOUND_EFFECT_FILES_MAP[effect][0]] = sampleId;
                            numSamples++;
                        }
                    } else {
                        SOUND_EFFECT_FILES_MAP[effect][1] =
                                poolId[SOUND_EFFECT_FILES_MAP[effect][0]];
                    }
                }
                // wait for all samples to be loaded
                if (numSamples > 0) {
                    mSoundPoolCallBack.setSamples(poolId);

                    attempts = 3;
                    status = 1;
                    while ((status == 1) && (attempts-- > 0)) {
                        try {
                            mSoundEffectsLock.wait(SOUND_EFFECTS_LOAD_TIMEOUT_MS);
                            status = mSoundPoolCallBack.status();
                        } catch (InterruptedException e) {
                            Log.w(TAG, "Interrupted while waiting sound pool callback.");
                        }
                    }
                } else {
                    status = -1;
                }

                if (mSoundPoolLooper != null) {
                    mSoundPoolLooper.quit();
                    mSoundPoolLooper = null;
                }
                mSoundPoolListenerThread = null;
                if (status != 0) {
                    Log.w(TAG,
                            "onLoadSoundEffects(), Error "+status+ " while loading samples");
                    for (int effect = 0; effect < AudioManager.NUM_SOUND_EFFECTS; effect++) {
                        if (SOUND_EFFECT_FILES_MAP[effect][1] > 0) {
                            SOUND_EFFECT_FILES_MAP[effect][1] = -1;
                        }
                    }

                    mSoundPool.release();
                    mSoundPool = null;
                }
            }
            return (status == 0);
        }

public void  playSoundEffect(int effectType) {
        if (effectType < 0 || effectType >= NUM_SOUND_EFFECTS) {
            return;
        }
        if (!querySoundEffectsEnabled(Process.myUserHandle().getIdentifier())) {
            return;
        }
        final IAudioService service = getService();
        try {
            service.playSoundEffect(effectType);
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

/** @see AudioManager#playSoundEffect(int) */
    public void playSoundEffect(int effectType) {
        playSoundEffectVolume(effectType, -1.0f);
    }

    /** @see AudioManager#playSoundEffect(int, float) */
    public void playSoundEffectVolume(int effectType, float volume) {
        // do not try to play the sound effect if the system stream is muted
        if (isStreamMutedByRingerOrZenMode(STREAM_SYSTEM)) {
            return;
        }

        if (effectType >= AudioManager.NUM_SOUND_EFFECTS || effectType < 0) {
            Log.w(TAG, "AudioService effectType value " + effectType + " out of range");
            return;
        }

        sendMsg(mAudioHandler, MSG_PLAY_SOUND_EFFECT, SENDMSG_QUEUE, // 发送消息
                effectType, (int) (volume * 1000), null, 0);
    }

case MSG_PLAY_SOUND_EFFECT:
                    onPlaySoundEffect(msg.arg1, msg.arg2);
                    break;

private void onPlaySoundEffect(int effectType, int volume) {
            synchronized (mSoundEffectsLock) {

                onLoadSoundEffects();    //上面提到过的的加载

                if (mSoundPool == null) {
                    return;
                }
                float volFloat;
                // use default if volume is not specified by caller
                if (volume < 0) {
                    volFloat = (float)Math.pow(10, (float)sSoundEffectVolumeDb/20);
                } else {
                    volFloat = volume / 1000.0f;
                }

                if (SOUND_EFFECT_FILES_MAP[effectType][1] > 0) {
                    mSoundPool.play(SOUND_EFFECT_FILES_MAP[effectType][1],
                                        volFloat, volFloat, 0, 0, 1.0f);
                } else {
                    MediaPlayer mediaPlayer = new MediaPlayer();
                    try {
                        String filePath = getSoundEffectFilePath(effectType);  //得到播放音频资源的地址。如果要替换资源，可以到此位置替换
                        mediaPlayer.setDataSource(filePath);
                        mediaPlayer.setAudioStreamType(AudioSystem.STREAM_SYSTEM);
                        mediaPlayer.prepare();
                        mediaPlayer.setVolume(volFloat);
                        mediaPlayer.setOnCompletionListener(new OnCompletionListener() {
                            public void onCompletion(MediaPlayer mp) {
                                cleanupPlayer(mp);
                            }
                        });
                        mediaPlayer.setOnErrorListener(new OnErrorListener() {
                            public boolean onError(MediaPlayer mp, int what, int extra) {
                                cleanupPlayer(mp);
                                return true;
                            }
                        });
                        mediaPlayer.start();     //开始播放
                    } catch (IOException ex) {
                        Log.w(TAG, "MediaPlayer IOException: "+ex);
                    } catch (IllegalArgumentException ex) {
                        Log.w(TAG, "MediaPlayer IllegalArgumentException: "+ex);
                    } catch (IllegalStateException ex) {
                        Log.w(TAG, "MediaPlayer IllegalStateException: "+ex);
                    }
                }
            }
        }