How to programmatically pair and connect a HID bluetooth device(Bluetooth Keyboard) on Android

Question

I am able to pair a bluetooth keyboard but not able to connect so as to make it an input device. I went through the documentation provided at developer site - http://developer.android.com/guide/topics/connectivity/bluetooth.html#Profiles

It says that the Android Bluetooth API provides implementations for the following Bluetooth profiles but you can implement the interface BluetoothProfile to write your own classes to support a particular Bluetooth profile.

• Headset
• A2DP
• Health Device

There is no documentation how to implement BluetoothProfile for HID bluetooth device(Keyboard)

Android has itself implemented bluetooth connection for HID devices but those API's are hidden. I tried reflection to use them too. I do not get any error but keyboard does not get connected as input device. This is what i have done -

private void connect(final BluetoothDevice bluetoothDevice) {
    if(bluetoothDevice.getBluetoothClass().getDeviceClass() == 1344){
        final BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
            BluetoothProfile.ServiceListener mProfileListener = new BluetoothProfile.ServiceListener() {
                @Override
                public void onServiceConnected(int profile, BluetoothProfile proxy) {
                    Log.i("btclass", profile + "");

                    if (profile == getInputDeviceHiddenConstant()) {
                        Class instance = null;
                        try {
                            //instance = Class.forName("android.bluetooth.IBluetoothInputDevice");
                            instance = Class.forName("android.bluetooth.BluetoothInputDevice");
                            Method connect = instance.getDeclaredMethod("connect", BluetoothDevice.class);
                            Object value = connect.invoke(proxy, bluetoothDevice);
                            Log.e("btclass", value.toString());
                        } catch (ClassNotFoundException e) {
                            e.printStackTrace();
                        } catch (InvocationTargetException e) {
                            e.printStackTrace();
                        } catch (NoSuchMethodException e) {
                            e.printStackTrace();
                        } catch (IllegalAccessException e) {
                            e.printStackTrace();
                        }



                    }
                }

                @Override
                public void onServiceDisconnected(int profile) {

                }
            };

            mBluetoothAdapter.getProfileProxy(this, mProfileListener,getInputDeviceHiddenConstant());


    }

}

public static int getInputDeviceHiddenConstant() {
    Class<BluetoothProfile> clazz = BluetoothProfile.class;
    for (Field f : clazz.getFields()) {
        int mod = f.getModifiers();
        if (Modifier.isStatic(mod) && Modifier.isPublic(mod) && Modifier.isFinal(mod)) {
            try {
                if (f.getName().equals("INPUT_DEVICE")) {
                    return f.getInt(null);
                }
            } catch (Exception e) {
                Log.e("", e.toString(), e);
            }
        }
    }
    return -1;
}

Answer 1

Due to security reasons, it is not possible for third party applications to connect to a bluetooth keyboard as the application can be a keylogger. So it can be only done manually by the user.

Answer 2

Here is the code I used on Android Marshmallow (6.0).. To get an L2CAP connection started (Needed for HID)

public static BluetoothSocket createL2CAPBluetoothSocket(String address, int psm){
    return createBluetoothSocket(BluetoothSocket.TYPE_L2CAP, -1, false,false, address, psm);
}

// method for creating a bluetooth client socket
private static BluetoothSocket createBluetoothSocket(int type, int fd, boolean auth, boolean encrypt, String address, int port){
    Log.e(TAG, "Creating socket with " + address + ":" + port);

    try {
        Constructor<BluetoothSocket> constructor = BluetoothSocket.class.getDeclaredConstructor(
                int.class, int.class,boolean.class,boolean.class,String.class, int.class);
        constructor.setAccessible(true);
        BluetoothSocket clientSocket = (BluetoothSocket) constructor.newInstance(type,fd,auth,encrypt,address,port);
        return clientSocket;
    }catch (Exception e) {
        e.printStackTrace();
    }

    return null;
}

public Boolean connect(View v) {

    try {
        // TODO: Check bluetooth enabled
        mDevice = getController();

        if (mDevice != null) {
            Log.e(TAG, "Controller is paired");

            // Create socket
            mSocket = createL2CAPBluetoothSocket(mDevice.getAddress(), 0x1124);

            if (mSocket != null) {

                if (!mSocket.isConnected()) {
                    mSocket.connect();
                }

                Log.e(TAG, "Socket successfully created");

                ConnectedThread mConnectedThread = new ConnectedThread(mSocket);
                mConnectedThread.run();
            }

        } else {
            showToast("Controller is not connected");
        }

        return true;

    } catch (Exception e) {
        e.printStackTrace();

        if (e instanceof IOException){
            // handle this exception type
        } else {
            // We didn't expect this one. What could it be? Let's log it, and let it bubble up the hierarchy.

        }

        return false;
    }
}

private BluetoothDevice getController() {
    Set<BluetoothDevice> pairedDevices = mBluetoothAdapter.getBondedDevices();

    if (pairedDevices.size() > 0) {
        for (BluetoothDevice device : pairedDevices) {
            if (device.getName().equals("Wireless Controller"))    // Change to match DS4 - node name
            {
                Log.d(TAG, "Found device named: " + device.getName());

                return device;
            }
        }
    }

    return null;
}

It can still have problems creating the Service, and you need to set the correct L2CAP PSAM for the device, but hope it can help..