Android - Bluetooth discovery doesn't find any device

Question

I'm currently working on a little app to get started with the services that the Bluetooth Android API can provide.

Edit -> Answer:

It seems that the issue was due to the specific Nexus 5 devices. Seems like their bluetooth receiver doesn't work well. Solution below should work for other devices

Remark:

1. I’ve read the documentation here: http://developer.android.com/guide/topics/connectivity/bluetooth.html as well as the following source code of this tutorial http://www.londatiga.net/it/programming/android/how-to-programmatically-scan-or-discover-android-bluetooth-device/ located on github under /lorensiuswlt/AndroBluetooth

2. I’ve finished almost all the features that interested me (such as check for adapter existence, enable/disable the blueooth, querying paired divices, set the adapter discoverable).

Issue:

Actually no device is found when i launch the .onDiscovery() method, even though devices are found from Settings/Bluetooth on my Nexus 5.

Here is how I handle it:

public class MainActivity extends AppCompatActivity {
private BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

...

protected void onCreate(Bundle savedInstanceState) {
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
filter.addAction(BluetoothDevice.ACTION_FOUND);
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_STARTED);
filter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
registerReceiver(mReceiver, filter); 
}

The filter is working well as far as i could try, i.e ACTION_STATE_CHANGED (on bluetooth enabling) and the two ACTION_DISCOVERY_***.

The following method is then successfuly called:

public void onDiscovery(View view)
{
    mBluetoothAdapter.startDiscovery();
}

And then i have my bluetooth receiver:

private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();

        if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
            final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);

            if (state == BluetoothAdapter.STATE_ON) {
                showToast("ACTION_STATE_CHANGED: STATE_ON");
            }
        }

        else if (BluetoothAdapter.ACTION_DISCOVERY_STARTED.equals(action)) {
            mDeviceList = new ArrayList<>();
            showToast("ACTION_DISCOVERY_STARTED");
            mProgressDlg.show();
        }

        else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action) && !bluetoothSwitchedOFF) {
            mProgressDlg.dismiss();
            showToast("ACTION_DISCOVERY_FINISHED");

            Intent newIntent = new Intent(MainActivity.this, DeviceListActivity.class);

            newIntent.putParcelableArrayListExtra("device.list", mDeviceList);

            startActivity(newIntent);
        }

        else if (BluetoothDevice.ACTION_FOUND.equals(action)) {// When discovery finds a device
            // Get the BluetoothDevice object from the Intent
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            mDeviceList.add(device);
            showToast("Device found = " + device.getName());
        }
    }
};

I don't have any issue coming out the logcat and didn't notice any trouble during the test I did. The only problem is that no device is discovered at the end of the scan, when many discoverable ones are available arround.

I tried to not put too much code in order to not flood the topic. Ask me if you need more.

Thanks for reading me, and thanks in advance for you answers.

Answer 1

What version of Android are you running this on? If it is Android 6.x, I believe you need to add the ACCESS_FINE_LOCATION permission to your manifest. For example:

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

I had a similar issue and this fixed it for me.

UPDATE: Adding documentation direct from Google on this:

To access the hardware identifiers of nearby external devices via Bluetooth and Wi-Fi scans, your app must now have the ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions

UPDATE 2020: We recently updated our application to target SDK Version 29. In doing this, our application stopped being able to discover Bluetooth devices again. We have been using ACCESS_COARSE_LOCATION since this answer was originally written. Changing to ACCESS_FINE_LOCATION appears to fix the issue. I now recommend developers try ACCESS_FINE_LOCATION if targeting 29+. Answer updated to reflect this.