How to talk to a Bluetooth keyboard?

Question

I\'ve written an Android app that connects to a Bluetooth keyboard. It connects through a BT socket to the keyboard and acquires the socket\'s input stream.

Answer 1

mringwal's answer is correct, besides the NDK approach, it is possible to use reflection on some devices, to achieve L2CAP connectivity:

public static BluetoothSocket createL2CAPBluetoothSocket(String address, int psm){
        return createBluetoothSocket(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){
        try {
            Constructor 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) { return null; }
    }

where TYPE_L2CAP is an integer having the constant value 3.

Note that this approach will only work on SOME android devices.

Writing a HID application is not a simple task. You need to implement a Report descriptor parser, a component used to "discover" the capabilities (special keys, functions) of a remote HID device. You will also need to learn the HID protocol and work flow , a copy is available here: http://www.dawidurbanski.pl/public/download/projekty/bluepad/HID_SPEC_V10.pdf

There are already professional programs doing exactly that, supporting HID on Android, see for example this software: http://teksoftco.com/index.php?section=product&pid=24

Because of Stack limitations, the L2CAP protocol is not available on all devices, so a solution that works on ALL devices is currently impossible.