最近一直在开发经典蓝牙，搞得头疼，网上资料太少。
参考链接：https://www.jianshu.com/p/94f8e3119981

https://www.bbsmax.com/A/WpdKB7Pr5V/

我需要在app中连接经典蓝牙用来播放歌曲，以及来录音。

在网上搜索经典蓝牙的连接，一大堆都是这种

   val socket =
                device.createInsecureRfcommSocketToServiceRecord(
UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"))
                println("连接服务端...")
                socket.connect()
                println("连接建立...")

但是这个连接上了之后一段时间不通信，就会自动断开，而且连接这个之后，播放音乐还是从手机的喇叭出来的。。

于是找了一下，看到了上面两片文章，音频使用a2dp来连接。

先看一下广播：

  private BroadcastReceiver mBluetoothBroadcast = new BroadcastReceiver() {

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction() == null) {
                return;
            }

            switch (intent.getAction()) {
                case BluetoothDevice.ACTION_BOND_STATE_CHANGED:
                    int bondState = intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, BluetoothDevice.BOND_NONE);
                    switch (bondState) {
                        case BluetoothDevice.BOND_BONDED:  //配对成功
                            a2dpConnect(mBluetoothDevice);  //连接蓝牙设备
                            break;
                        case BluetoothDevice.BOND_NONE:
                            mBluetoothDevice.createBond();
                            break;
                        default:
                            break;
                    }
                    break;

                case BluetoothA2dp.ACTION_CONNECTION_STATE_CHANGED:
                    if (intent.getIntExtra(BluetoothA2dp.EXTRA_STATE, -1) == BluetoothA2dp.STATE_CONNECTED) {
                        Toast.makeText(context, "绑定成功", Toast.LENGTH_SHORT).show();
                    }
                    break;

                case AudioManager.ACTION_SCO_AUDIO_STATE_UPDATED:
                    int state = intent.getIntExtra(AudioManager.EXTRA_SCO_AUDIO_STATE, -1);
                    if (AudioManager.SCO_AUDIO_STATE_CONNECTED == state) {
                        mAudioManager.setBluetoothScoOn(true);
                    //开启录音～
                    }
                    break;
            }
        }
    };

先获取a2dp对象

  mBluetoothAdapter.getProfileProxy(this, new BluetoothProfile.ServiceListener() {
            @Override
            public void onServiceConnected(int profile, BluetoothProfile proxy) {
                if (profile == BluetoothProfile.A2DP) {
                    mBluetoothA2dp = (BluetoothA2dp) proxy;
                }
            }

            @Override
            public void onServiceDisconnected(int profile) {

            }
        }, BluetoothProfile.A2DP);

然后判断A2DP连接上没有

    public boolean getA2dpState(BluetoothDevice device) {
        return mBluetoothA2dp != null && mBluetoothA2dp.getConnectionState(device) ==
                BluetoothProfile.STATE_CONNECTED;
    }

连接成功，就开始录音或者播放音乐：

mAudioManager.stopBluetoothSco();
 mAudioManager.startBluetoothSco();

没有连接成功就先配对设备，然后连接

mBluetoothDevice.createBond(); //配对设备
    public void a2dpConnect(BluetoothDevice device) {
        if (mBluetoothA2dp != null) {
            Class<? extends BluetoothA2dp> clazz = mBluetoothA2dp.getClass();
            Method m2;
            try {
                Log.i(TAG, "use reflect to connect a2dp");
                m2 = clazz.getMethod("connect", BluetoothDevice.class);
                m2.invoke(mBluetoothA2dp, device);
            } catch (Exception e) {
                Log.e(TAG, "error:" + e.toString());
            }
        }
    }

然后这些事件的回调都在那个广播中收到。。。