Android 蓝牙 StartDiscovery() 总是返回 false

Question

我试图发现附近的蓝牙设备，但 startDiscovery() 总是返回 false，就好像它不工作一样。因此它无法找到设备。

我看到除了蓝牙和 Bluetooth_Admin 之外，我必须包含 Coarse_Location 权限，但无论如何，它不起作用。

这是我现在正在尝试的代码，其中主要有痕迹可以看到它是如何工作的:

public class BluetoothActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    ArrayList<BluetoothDevice> dispositivos;
    BTAdapter adaptador;
    BluetoothAdapter mBluetoothAdapter;
    Button buscar;

    final int REQUEST_ACCESS_COARSE_LOCATION = 16;
    @Override
    public void onCreate(Bundle savedInsanceState){
        super.onCreate(savedInsanceState);
        setContentView(R.layout.bluetooth_activity);

        recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

        if(mBluetoothAdapter != null) {
            Toast.makeText(this, "No es nulo", Toast.LENGTH_SHORT).show();
            if (!mBluetoothAdapter.isEnabled()) {
                Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                startActivityForResult(intent, RESULT_OK);
            }

            IntentFilter filter = new IntentFilter();

            filter.addAction(BluetoothDevice.ACTION_FOUND);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);

            registerReceiver(mReceiver, filter);

        }

        buscar = findViewById(R.id.buscar);
        buscar.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(BluetoothActivity.this, "Empezar a buscar", Toast.LENGTH_SHORT).show();

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                    switch (ContextCompat.checkSelfPermission(BluetoothActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION)) {
                        case PackageManager.PERMISSION_DENIED:
                            ActivityCompat.requestPermissions(BluetoothActivity.this,
                                    new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
                                    REQUEST_ACCESS_COARSE_LOCATION);

                            break;
                        case PackageManager.PERMISSION_GRANTED:
                            boolean a = mBluetoothAdapter.startDiscovery();
                            Toast.makeText(BluetoothActivity.this, "Start discovery es "+a, Toast.LENGTH_SHORT).show();
                            break;
                    }
                }
            }
        });
    }

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if(BluetoothDevice.ACTION_FOUND.equals(action)){
                Toast.makeText(BluetoothActivity.this, "Encontrado", Toast.LENGTH_SHORT).show();
            }
        }
    };

    @Override
    public void onRequestPermissionsResult(int requestCode,
                                           String permissions[], int[] grantResults) {
        switch (requestCode) {
            case REQUEST_ACCESS_COARSE_LOCATION: {
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    boolean a = mBluetoothAdapter.startDiscovery();
                    Toast.makeText(BluetoothActivity.this, "Start discovery es "+a, Toast.LENGTH_SHORT).show();
                }
                else {
                    //exit application or do the needful
                }
                return;
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(mReceiver);
    }


}

这里是android list 中的权限:

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.BLUETOOTH"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

    <uses-feature android:name="android.hardware.bluetooth" />

更新:当我点击查看 startDiscovery 方法的描述时，我得到了这个，RequiresPermission 和 startDiscovery 是红色的，说“无法解析方法”和 Manifest.permission.BLUETOOTH_ADMIN 下划线并说“找不到方法值”:

@RequiresPermission(Manifest.permission.BLUETOOTH_ADMIN)
    public boolean startDiscovery() {
        if (getState() != STATE_ON) {
            return false;
        }
        try {
            mServiceLock.readLock().lock();
            if (mService != null) {
                return mService.startDiscovery(getOpPackageName());
            }
        } catch (RemoteException e) {
            Log.e(TAG, "", e);
        } finally {
            mServiceLock.readLock().unlock();
        }
        return false;
    }

Answer 1

您是否检查过该位置已在您的设备上激活？
即使授予位置权限，当它被禁用时，蓝牙 API 也不起作用。
所以我建议你添加以下代码以确保权限有效:

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
boolean isGpsEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
if (!isGpsEnabled) {
  startActivityForResult(new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS), MY_REQUEST_CODE);
}