Android – Bluetooth pairing – how to show the simple Cancel/Pair dialog

androidandroid-bluetoothandroid-intentbluetoothbluetooth-oob

I have prepared a simple test project for this question at GitHub.

I am trying to create an Android app, which would scan a QR code from a computer screen and then use the data (MAC address and PIN or hash) for easy pairing (bonding) with a Bluetooth device.

Similar to the popular InstaWifi app – but for Classic Bluetooth.

For testing purposes I don't do any barcode scanning yet, but just display a list of devices:

list of devices

After user touches one of the devices, pairing is tried in MainActivity.java:

private void startBluetoothPairing(BluetoothDevice device) {
    Intent pairingIntent = new Intent(BluetoothDevice.ACTION_PAIRING_REQUEST);
    pairingIntent.putExtra(BluetoothDevice.EXTRA_DEVICE, device);
    pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT,
                BluetoothDevice.PAIRING_VARIANT_PIN);
    pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_KEY, 1234);
    //device.setPin(new byte[]{1,2,3,4});  <- DOES NOT CHANGE ANYTHING
    //device.setPairingConfirmation(false);
    startActivityForResult(pairingIntent, REQUEST_BT_SETTINGS);
}

Unfortunately, the popup still asks for PIN:

pin dialog

Because I have actually specified a PIN in my source code, I was actually expecting another, simpler system dialog to be shown (this one is shown when doing NFC OOB pairing):

pair dialog

From searching for solutions, I know that there is a setPin() method, but it is not applicable here (or is it?) – because I am trying to pair the whole smartphone to the Bluetooth device and not just the app…

My question: How to make Android OS to show the simple Cancel/Pair dialog?

Searching for Bluetooth pairing request string at GitHub has not shown any hints…

UPDATE: On unrealsoul007's suggestion (thanks) I have update the source code in MainActivity.java and now the simple Cancel/Pair dialog is displayed:

private void startBluetoothPairing(BluetoothDevice device) {
    Intent pairingIntent = new Intent(BluetoothDevice.ACTION_PAIRING_REQUEST);
    pairingIntent.putExtra(BluetoothDevice.EXTRA_DEVICE, device);
    pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT,
        BluetoothDevice.PAIRING_VARIANT_PASSKEY_CONFIRMATION);
    pairingIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    startActivityForResult(pairingIntent, REQUEST_BT_PAIRING);
}

However I am not sure how to complete the pairing process – because onActivityResult is called with resultCode=0 even before the dialog is closed:

@Override
public void onActivityResult(int requestCode, int resultCode, Intent intent) {
    // this is called before user clicks Cancel or Pair in the dialog
    if (requestCode == REQUEST_BT_PAIRING) { 
        if (resultCode == Activity.RESULT_OK) {  // 0 != -1
            Log.d("XXX", "Let#s pair!!!!"); // NOT CALLED
        }

        return;
    }
}

Best Answer

You are being prompted for entering the pin because that is what you are requesting in your pairingIntent.

Instead of using

pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT,
                BluetoothDevice.PAIRING_VARIANT_PIN);
pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_KEY, 1234);

Use

pairingIntent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT, PAIRING_VARIANT_PASSKEY_CONFIRMATION);

As mentioned here,

The user will be prompted to confirm the passkey displayed on the screen or an app will confirm the passkey for the user.

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Android – How to close/hide the Android soft keyboard programmatically

You can force Android to hide the virtual keyboard using the InputMethodManager, calling hideSoftInputFromWindow, passing in the token of the window containing your focused view.

// Check if no view has focus:
View view = this.getCurrentFocus();
if (view != null) {  
    InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
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This will force the keyboard to be hidden in all situations. In some cases, you will want to pass in InputMethodManager.HIDE_IMPLICIT_ONLY as the second parameter to ensure you only hide the keyboard when the user didn't explicitly force it to appear (by holding down the menu).

Note: If you want to do this in Kotlin, use: context?.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager

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Android – How to programmatically pair a bluetooth device on Android

I managed to auto request a pairing procedure with keyboard featured devices through an app working as a service checking the presence of a specific kind of device and a modified version of the Settings app.

I have to say that I was working on a custom device running Android 4.0.3 without external controls (no back/Home/confirm buttons): pairing a controller on boot complete without any interaction until PIN request was mandatory.

First I created a service starting an activity on boot (with android.intent.action.BOOT_COMPLETED and android.permission.RECEIVE_BOOT_COMPLETED) that checks periodically the presence of a 1344 class device (a keyboard, the only way to input data on request) on the onReceive callback:

public void onReceive(Context context, Intent intent) 
...
    BluetoothDevice dev = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
...
if(dev.getBluetoothClass().getDeviceClass() == 1344){...}

Once filtered I choose the first keyboard available and then I pass the BT address to the Settings app:

Intent btSettingsIntent = new Intent(Settings.ACTION_BLUETOOTH_SETTINGS);
btSettingsIntent.putExtra("btcontroller", dev.getAddress());
startActivityForResult(btSettingsIntent, 1);

The tricky part was looking for the best position to call the pairing process. Using only the

intent.putExtra(BluetoothDevice.EXTRA_PAIRING_VARIANT, PAIRING_VARIANT_PIN);

led me to a paring dialog that once closed left me with the device paired, but unusable.

Digging into the classes of com.Android.settings.Bluetooth I found my way through the

createDevicePreference(CachedBluetoothDevice cachedDevice)

in the DeviceListPreferenceFragment.

From there I did compare my previously selected BT address with those available coming up and once successfully matched I call

cachedDevice.startPairing();

I know, it's tricky and requires access to the Android source code, but in a custom environment it works.

I hope this could be helpful.

Best Answer

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