Android - Bluetooth discovery doesn't find any

问题:

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.

回答1:

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

<uses-permission android:name="android.permission.ACCESS_COARSE_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

回答2:

Bit late to the party but this may come in handy for other people.

You need to do two things

1. Add <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

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

to your AndroidManifest.xml

2. Make sure you're requesting the permission on runtime as well for Android 6.0 Devices by using something like this

   int MY_PERMISSIONS_REQUEST_ACCESS_COARSE_LOCATION = 1; 
   ActivityCompat.requestPermissions(this,
           new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
           MY_PERMISSIONS_REQUEST_ACCESS_COARSE_LOCATION);
   

   just before mBluetoothAdapter.startDiscovery();

If you don't do step 2 you won't be able to get any Hardware Identifier info on device with Android >= 6.0

UPDATE/EDIT:
Example with Android Version check and alert dialog as warning

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {  // Only ask for these permissions on runtime when running Android 6.0 or higher
    switch (ContextCompat.checkSelfPermission(getBaseContext(), Manifest.permission.ACCESS_COARSE_LOCATION)) {
        case PackageManager.PERMISSION_DENIED:
            ((TextView) new AlertDialog.Builder(this)
                    .setTitle("Runtime Permissions up ahead")
                    .setMessage(Html.fromHtml("<p>To find nearby bluetooth devices please click \"Allow\" on the runtime permissions popup.</p>" +
                            "<p>For more info see <a href=\"http://developer.android.com/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id\">here</a>.</p>"))
                    .setNeutralButton("Okay", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            if (ContextCompat.checkSelfPermission(getBaseContext(), Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                                ActivityCompat.requestPermissions(DeviceListActivity.this,
                                        new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
                                        REQUEST_ACCESS_COARSE_LOCATION);
                            }
                        }
                    })
                    .show()
                    .findViewById(android.R.id.message))
                    .setMovementMethod(LinkMovementMethod.getInstance());       // Make the link clickable. Needs to be called after show(), in order to generate hyperlinks
            break;
        case PackageManager.PERMISSION_GRANTED:
            break;
    }
}