Android 控制车载蓝牙播放音乐详解流程

需求：手机端音乐暂停和播放状态从服务端告诉客户端、设备端实现暂停、播放、上一首、下一首等功能
代码路径：

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

一、蓝牙音乐播放状态

1、在avrcpcontrollerservice.java文件中onplaystatuschanged()方法就是音乐播放状态改变，该方法是由jni层中com_android_bluetooth_avrcp_controller.cpp中调用java层的

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、在avrcpcontrollerstatemachine.java文件中connected类中

message_process_play_status_changed消息就是处理播放状态的，然后通过广播方式把该状态发送出去

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) {
                //播放
                    a2dpsinkservice.informplaystate(mdevice, true);
            } else if (msg.arg1 == playbackstate.state_paused) {
                //暂停
                    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;

二、蓝牙音乐中怎么获取音乐信息

1、在avrcpcontrollerservice.java文件中ontrackchanged()方法中是获取jni层上报的音乐信息，该方法是由jni层中com_android_bluetooth_avrcp_controller.cpp中调用java层的

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);
    //该方法就是把蓝牙音乐的信息传递给java层
    getelementattrrsp(attributes,attribvals,numattributes);
    if (statemachine != null) {
        statemachine.sendmessage(avrcpcontrollerstatemachine.message_process_track_changed,
                trackinfo.getmetadata(attributes, attribvals));
    }
}

2、在avrcpcontrollerservice.java文件中getelementattrrsp()中，然后通过该方法中通过广播告诉出去

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);
}

三、设备蓝牙音乐中上一首、下一首、暂停功能控制手机端

1、在avrcpcontrollerservice.java文件中sendpassthroughcmd()方法来控制暂停、播放、上一首、下一首等功能

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、在avrcpcontrollerstatemachine.java文件中message_send_pass_through_cmd变量中通过jni层来实现功能

case message_send_pass_through_cmd:
    bluetoothdevice device = (bluetoothdevice) msg.obj;
    mservice.sendpassthroughcommandnative(utils.getbyteaddress(device), msg.arg1,
                    msg.arg2);
    return true;

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