Android Control Vehicle Bluetooth Music Play Detailed Explanation Flow

Requirements: The status of music pause and play on the mobile phone is told to the client from the server, and the device realizes the functions of pause, play, top one and bottom one, etc.
Code path:

packages/apps/Bluetooth/src/com/android/bluetooth/avrcpcontroller/AvrcpControllerService.java
packages/apps/Bluetooth/src/com/android/bluetooth/avrcpcontroller/AvrcpControllerStateMachine.java
packages/apps/Bluetooth/src/com/android/bluetooth/a2dpsink/A2dpSinkService.java
packages/apps/Bluetooth/src/com/android/bluetooth/avrcpcontroller/AvrcpControllerService.java
packages/apps/Bluetooth/jni/com_android_bluetooth_avrcp_controller.cpp

1. Bluetooth music playback status

1. The onPlayStatusChanged () method in the AvrcpControllerService. java file is the music playback state change, which is called java layer from com_android_bluetooth_avrcp_controller. cpp in JNI layer

private synchronized void onPlayStatusChanged(byte[] address, byte playStatus) {
    if (DBG) {
        Log.d(TAG, "onPlayStatusChanged " + playStatus);
    }
    int playbackState = PlaybackState.STATE_NONE;
    switch (playStatus) {
        case JNI_PLAY_STATUS_STOPPED:
            playbackState = PlaybackState.STATE_STOPPED;
            break;
        case JNI_PLAY_STATUS_PLAYING:
            playbackState = PlaybackState.STATE_PLAYING;
            break;
        case JNI_PLAY_STATUS_PAUSED:
            playbackState = PlaybackState.STATE_PAUSED;
            break;
        case JNI_PLAY_STATUS_FWD_SEEK:
            playbackState = PlaybackState.STATE_FAST_FORWARDING;
            break;
        case JNI_PLAY_STATUS_REV_SEEK:
            playbackState = PlaybackState.STATE_REWINDING;
            break;
        default:
            playbackState = PlaybackState.STATE_NONE;
    }
    BluetoothDevice device = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(address);
    AvrcpControllerStateMachine stateMachine = getStateMachine(device);
    if (stateMachine != null) {
        stateMachine.sendMessage(
                AvrcpControllerStateMachine.MESSAGE_PROCESS_PLAY_STATUS_CHANGED, playbackState);
    }
}

2. In the Connected class in the AvrcpControllerStateMachine. java file

The MESSAGE_PROCESS_PLAY_STATUS_CHANGED message handles the playback status and then sends the status through broadcasting

case MESSAGE_PROCESS_PLAY_STATUS_CHANGED:
    if (SystemProperties.get("persist.ivi.feature", "0").equals("1")) {
        A2dpSinkService a2dpSinkService = A2dpSinkService.getA2dpSinkService();
        Log.d(TAG, "the state: " + msg.arg1);
        if (a2dpSinkService != null && msg.arg1 != preAudioStatus) {
            preAudioStatus = msg.arg1;
            Log.d(TAG, "preAudioStatus: " + msg.arg1);
            if (msg.arg1 == PlaybackState.STATE_PLAYING) {
                // Play 
                    a2dpSinkService.informPlayState(mDevice, true);
            } else if (msg.arg1 == PlaybackState.STATE_PAUSED) {
                // Suspend 
                    a2dpSinkService.informPlayState(mDevice, false);
            }
        }
    }
    Intent intent = new Intent("zqc.bluetooth.PLAY_STATUS_CHANGED");
intent.putExtra("zqc.bluetooth.PLAYBACK", msg.arg1);
mService.sendBroadcast(intent);
    mAddressedPlayer.setPlayStatus(msg.arg1);
    BluetoothMediaBrowserService.notifyChanged(mAddressedPlayer.getPlaybackState());
    if (mAddressedPlayer.getPlaybackState().getState()
            == PlaybackState.STATE_PLAYING
            && A2dpSinkService.getFocusState() == AudioManager.AUDIOFOCUS_NONE
            && !shouldRequestFocus()) {
        sendMessage(MSG_AVRCP_PASSTHRU,
                AvrcpControllerService.PASS_THRU_CMD_ID_PAUSE);
    }
    return true;

2. How to get music information in Bluetooth music

1. In the onTrackChanged () method in the AvrcpControllerService. java file, the music information reported by the JNI layer is obtained. The method calls the java layer from com_android_bluetooth_avrcp_controller. cpp in the JNI layer

private synchronized void onTrackChanged(byte[] address, byte numAttributes, int[] attributes,
        String[] attribVals) {
    if (DBG) {
        Log.d(TAG, "onTrackChanged");
    }

    BluetoothDevice device = BluetoothAdapter.getDefaultAdapter().getRemoteDevice(address);
    AvrcpControllerStateMachine stateMachine = getStateMachine(device);
    // The method is to transmit the information of Bluetooth music to java Layer 
    getElementAttrRsp(attributes,attribVals,numAttributes);
    if (stateMachine != null) {
        stateMachine.sendMessage(AvrcpControllerStateMachine.MESSAGE_PROCESS_TRACK_CHANGED,
                TrackInfo.getMetadata(attributes, attribVals));
    }
}

2. In getElementAttrRsp () in the AvrcpControllerService. java file, and then broadcast it through this method

private void getElementAttrRsp(int[] attr_id,String[] textArray,byte num_attr){
    String artist = null;
    String trackTitle = null;
    String album = null;
    for (int i = 0; i < num_attr; i++){
        switch (attr_id[i]) {
            case JNI_MEDIA_ATTR_ID_TITLE:
                trackTitle = textArray[i];
                if (trackTitle == null){
                    trackTitle = "Unknown";
                }
                break;
            case JNI_MEDIA_ATTR_ID_ARTIST:
                artist = textArray[i];
                if (artist == null){
                    artist = "Unknown";
                }
                break;
            case JNI_MEDIA_ATTR_ID_ALBUM:
                album = textArray[i];
                if (album == null){
                    album = "Unknown";
                }
                break;
        }
    }
    Intent intent = new Intent("com.android.getelementattrrsp");
    intent.putExtra("artist", artist);
    intent.putExtra("trackTitle",trackTitle);
    intent.putExtra("album",album);
    Log.d(TAG,"getElementAttrRsp,artist: " + artist + ",trackTitle: " + trackTitle + ",album: " + album);
    intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND);
    sendBroadcast(intent, ProfileService.BLUETOOTH_PERM);
}

3. The upper one and the lower one in the Bluetooth music of the device, and the pause function controls the mobile phone

1. In the AvrcpControllerService. java file, sendPassThroughCmd () method is used to control the functions of pause, play, top 1, bottom 1, etc.

public synchronized void sendPassThroughCmd(BluetoothDevice device, int keyCode, int keyState) {
    Log.v(TAG, "sendPassThroughCmd keyCode: " + keyCode + " keyState: " + keyState);
    if (device == null) {
        Log.e(TAG, "sendPassThroughCmd Device is null");
        return;
    }

    AvrcpControllerStateMachine stateMachine = getStateMachine(device);
    if (stateMachine != null) {
        stateMachine.sendMessage(AvrcpControllerStateMachine.MESSAGE_SEND_PASS_THROUGH_CMD,
            keyCode, keyState, device);
    }
}

2. The function is realized by JNI layer in MESSAGE_SEND_PASS_THROUGH_CMD variable in AvrcpControllerStateMachine. java file

case MESSAGE_SEND_PASS_THROUGH_CMD:
    BluetoothDevice device = (BluetoothDevice) msg.obj;
    mService.sendPassThroughCommandNative(Utils.getByteAddress(device), msg.arg1,
                    msg.arg2);
    return true;