How to detect if bluetooth device is connected

Question

In android how can my Activity will get to know if a Bluetooth A2DP device is connected to my device.
Is there any broadcast receiver for that?
How to write this broadcast receiver?

Answer 1

Starting from API 11 (Android 3.0) you can use BluetoothAdapter to discover devices connected to a specific bluetooth profile. I used the code below to discover a device by its name:

BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
BluetoothProfile.ServiceListener mProfileListener = new BluetoothProfile.ServiceListener() {
        public void onServiceConnected(int profile, BluetoothProfile proxy) {
            if (profile == BluetoothProfile.A2DP) {
                boolean deviceConnected = false;
                BluetoothA2dp btA2dp = (BluetoothA2dp) proxy;
                List<BluetoothDevice> a2dpConnectedDevices = btA2dp.getConnectedDevices();
                if (a2dpConnectedDevices.size() != 0) {
                    for (BluetoothDevice device : a2dpConnectedDevices) {
                        if (device.getName().contains("DEVICE_NAME")) {
                            deviceConnected = true;
                        }
                    }
                }
                if (!deviceConnected) {
                    Toast.makeText(getActivity(), "DEVICE NOT CONNECTED", Toast.LENGTH_SHORT).show();
                }
                mBluetoothAdapter.closeProfileProxy(BluetoothProfile.A2DP, btA2dp);
            }
        }

        public void onServiceDisconnected(int profile) {
            // TODO
        }
    };
mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.A2DP);

You can do that for every bluetooth profile. Take a look at Working with profiles in Android's guide.

However, as written in other answers, you can register a BroadcastReceiver to listen to connection events (like when you're working on android < 3.0).