Android蓝牙API找不到任何设备

Question

I am trying to implement a Bluetooth device discovery function in my app. I have implemented the proposed way to do it with a BluetoothAdapter and a BroadcastReceiver like so:

My Activity (discover() is called in onCreate):

    public class MapsActivity extends AppCompatActivity implements OnMapReadyCallback {
        BluetoothAdapter mBluetoothAdapter;
        private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
            public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();

                //Finding devices
                if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
                    //discovery starts, we can show progress dialog or perform other tasks
                    testDevice("Start discover");
                } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                    //discovery finishes, dismis progress dialog
                    testDevice("Discovery finished");
                } else if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                    //bluetooth device found
                    BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                    testDevice("Found device " + device.getName());
                }
            }
        };

        public void discover() {
            this.mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

            IntentFilter filter = new IntentFilter();

            filter.addAction(BluetoothDevice.ACTION_FOUND);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
            filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
            registerReceiver(mReceiver, filter);
            mBluetoothAdapter.startDiscovery();
        }

        public void testDevice(String msg) {
                Toast.makeText(this, msg,
                        Toast.LENGTH_LONG).show();
        }

}

In my manifest I have the following permissions:

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

The result is me getting two toasts: "Start discovery" and 10sec later "Discovery finished". Never a device is found. I have tested on Samsung S9+, Sansumg Tab A, and Motorola something (with Bluetooth on).

Is there something I am not doing wright or is there any known problems I don't know?

Answer 1

Pure speculation on my end, but in case you're running on API level 23 + (and likely you are), you need to dynamically ask for permissions, not just declare them in manifest. Either use RxPermissions or ContextCompat.checkSelfPermission .