Android Bluetooth | 蓝牙配对源码分析

好厚米们，我又来了！

这次分享的是蓝牙设备执行配对动作时Android源码的执行流程。

下面先来说下，应用层是如何发起蓝牙配对的：

（ ps:大多数业务逻辑，都是扫描到可用设备后，点击可用设备 -> 发起配对。）

这里我直接略过点击可用设备的步骤哈，扫描到第一个可用设备后，我直接通过扫描信息进行配对。

public class MainActivity extends AppCompatActivity {
    private BluetoothAdapter mBluetoothAdapter;
    private BluetoothDevice mBluetoothDevice;
    private BluetoothLeScanner scanner = BluetoothAdapter.getDefaultAdapter().getBluetoothLeScanner();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ScanCallback scanCallback = new ScanCallback() {
            @SuppressLint("MissingPermission")
            @Override
            public void onScanResult(int callbackType, ScanResult result) {
                super.onScanResult(callbackType, result);
           
                //将扫描到的设备信息取出来，为蓝牙设备赋值
                mBluetoothDevice = result.getDevice();
                //通过蓝牙设备，调用配对方法
                mBluetoothDevice.createBond();
            }
            @Override
            public void onScanFailed(int errorCode) {
                super.onScanFailed(errorCode);
                // 扫描失败处理
            }
        };
        // 开始扫描
        if (scanner != null) {
            ScanSettings settings = new ScanSettings.Builder()
                    .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                    .build();
            // 添加过滤条件
            List<ScanFilter> filters = new ArrayList<>();
            //权限检查
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_SCAN) != PackageManager.PERMISSION_GRANTED) {
                // TODO: Consider calling
                //    ActivityCompat#requestPermissions
                // here to request the missing permissions, and then overriding
                //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
                //                                          int[] grantResults)
                // to handle the case where the user grants the permission. See the documentation
                // for ActivityCompat#requestPermissions for more details.
                return;
            }
            scanner.startScan(filters, settings, scanCallback);
        }
            // 停止扫描
        if (scanner != null) {
            scanner.stopScan(scanCallback);
        }

        mBluetoothAdapter.startDiscovery();

    }
}

由上面的代码可以看出，配对动作的执行依赖

 //通过蓝牙设备，调用配对方法
 BluetoothDevice.createBond();

下面就进入到了FWK层

执行BluetoothDevice.createBond()后，会进入到BluetoothDevice.java中执行

BluetoothDevice.java - OpenGrok cross reference for /frameworks/base/core/java/android/bluetooth/BluetoothDevice.java

 public boolean createBond() {
           final IBluetooth service = sService;
          if (service == null) {
             Log.e(TAG, "BT not enabled. Cannot create bond to Remote Device");
              return false;
          }
           try {
              Log.i(TAG, "createBond() for device " + getAddress()
                      + " called by pid: " + Process.myPid()
                      + " tid: " + Process.myTid());
                //通过service接口执行配对动作
              return service.createBond(this, TRANSPORT_AUTO);
           } catch (RemoteException e) {
               Log.e(TAG, "", e);
          }
           return false;
      }

而这个service，我们来看下其声明

private static volatile IBluetooth sService;

//后来在上面的配对方法中，为此接口赋值
final IBluetooth service = sService;

本质上就是IBluetooth接口，不过在Android 10中，IBluetooth接口一共有两个。

应用层下发配对动作时，所用的IBludetooth接口是/system/bt/service/common/android/bluetooth/

此接口的具体代码如下(太多了，各位厚米自己点连接看下就行)：

IBluetooth.aidl - OpenGrok cross reference for /system/bt/binder/android/bluetooth/IBluetooth.aidl

即通过这个AIDL接口调用蓝牙远程服务。

下面进入了Bluetooth 服务层

而这个接口的实现