How to programmatically tell if a Bluetooth device is connected?

Question

I understand how to get a list of paired devices but how can I tell if they are connected?

It must be possible since I see them listed in my phone\'s Bluetooth devi

Answer 1

In my use case I only wanted to see if a Bluetooth headset is connected for a VoIP app. The following solution worked for me:

public static boolean isBluetoothHeadsetConnected() {
    BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    return mBluetoothAdapter != null && mBluetoothAdapter.isEnabled()
            && mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED;
} 

Of course you'll need the Bluetooth permission:

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

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Answer 2

BluetoothAdapter.getDefaultAdapter().isEnabled -> returns true when bluetooth is open

val audioManager = this.getSystemService(Context.AUDIO_SERVICE) as AudioManager

audioManager.isBluetoothScoOn -> returns true when device connected

Answer 3

I was really looking for a way to fetch the connection status of a device, not listen to connection events. Here's what worked for me:

BluetoothManager bm = (BluetoothManager) context.getSystemService(Context.BLUETOOTH_SERVICE);
List<BluetoothDevice> devices = bm.getConnectedDevices(BluetoothGatt.GATT);
int status = -1;

for (BluetoothDevice device : devices) {
  status = bm.getConnectionState(device, BLuetoothGatt.GATT);
  // compare status to:
  //   BluetoothProfile.STATE_CONNECTED
  //   BluetoothProfile.STATE_CONNECTING
  //   BluetoothProfile.STATE_DISCONNECTED
  //   BluetoothProfile.STATE_DISCONNECTING
}

Answer 4

Add bluetooth permission to your AndroidManifest,

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

Then use intent filters to listen to the ACTION_ACL_CONNECTED, ACTION_ACL_DISCONNECT_REQUESTED, and ACTION_ACL_DISCONNECTED broadcasts:

public void onCreate() {
    ...
    IntentFilter filter = new IntentFilter();
    filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);
    filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED);
    filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
    this.registerReceiver(mReceiver, filter);
}

//The BroadcastReceiver that listens for bluetooth broadcasts
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);

        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
           ... //Device found
        }
        else if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
           ... //Device is now connected
        }
        else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
           ... //Done searching
        }
        else if (BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED.equals(action)) {
           ... //Device is about to disconnect
        }
        else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
           ... //Device has disconnected
        }           
    }
};

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A few notes:

• There is no way to retrieve a list of connected devices at application startup. The Bluetooth API does not allow you to QUERY, instead it allows you to listen to CHANGES.
• A hoaky work around to the above problem would be to retrieve the list of all known/paired devices... then trying to connect to each one (to determine if you're connected).
• Alternatively, you could have a background service watch the Bluetooth API and write the device states to disk for your application to use at a later date.

Answer 5

There is an isConnected function in BluetoothDevice system API in https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/bluetooth/BluetoothDevice.java

If you want to know if the a bounded(paired) device is currently connected or not, the following function works fine for me:

public static boolean isConnected(BluetoothDevice device) {
    try {
        Method m = device.getClass().getMethod("isConnected", (Class[]) null);
        boolean connected = (boolean) m.invoke(device, (Object[]) null);
        return connected;
    } catch (Exception e) {
        throw new IllegalStateException(e);
    }
}

Answer 6

This code is for the headset profiles, probably it will work for other profiles too. First you need to provide profile listener (Kotlin code):

private val mProfileListener = object : BluetoothProfile.ServiceListener {
    override fun onServiceConnected(profile: Int, proxy: BluetoothProfile) {
        if (profile == BluetoothProfile.HEADSET) 
            mBluetoothHeadset = proxy as BluetoothHeadset            
    }

    override fun onServiceDisconnected(profile: Int) {
        if (profile == BluetoothProfile.HEADSET) {
            mBluetoothHeadset = null
        }
    }
}

Then while checking bluetooth:

mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.HEADSET)
if (!mBluetoothAdapter.isEnabled) {
    return Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
}

It takes a bit of time until onSeviceConnected is called. After that you may get the list of the connected headset devices from:

mBluetoothHeadset!!.connectedDevices