Manage calls using the Telecom API

This guide covers how to route audio for Bluetooth devices using the Telecom API and set the connection for VoIP calls. Read the Build a calling app guide before continuing.

By using the ConnectionService and Connection classes, you can access the audio state and a list of available Bluetooth devices, and can route audio to a selected Bluetooth device.

VoIP Connection and ConnectionService

Create a VoIPConnection class that extends from Connection. This class controls the state of the current call. As the Build a calling app guide states, make this a self-managed application and set the audio mode for a VoIP application.

class VoIPConnection : Connection() {
  init {
    setConnectionProperties(PROPERTY_SELF_MANAGED)
    setAudioModeIsVoip(true)
  }
}

public class VoIPConnection extends Connection {
  public VoIPConnection() {
    setConnectionProperties(PROPERTY_SELF_MANAGED);
    setAudioModeIsVoip(true);
  }
}

Next, return an instance of this class in ConnectionService when an incoming or outgoing call occurs.

class VoIPConnectionService : ConnectionService() {
  override fun onCreateOutgoingConnection(
    connectionManagerPhoneAccount: PhoneAccountHandle,
    request: ConnectionRequest,
  ): Connection {
    return VoIPConnection()
  }
}

public class VoIPConnectionService extends ConnectionService {
  @Override
  public Connection onCreateOutgoingConnection(PhoneAccountHandle connectionManagerPhoneAccount, ConnectionRequest request) {
    return new VoIPConnection();
  }
}

Ensure the manifest correctly points to the VoIPConnectionService class.

<service android:name=".voip.TelegramConnectionService" android:permission="android.permission.BIND_TELECOM_CONNECTION_SERVICE">
  <intent-filter>
    <action android:name="android.telecom.ConnectionService"/>
  </intent-filter>
</service>

With these custom Connection and ConnectionService classes, you can control which device and what type of audio routing you wish to use during a call.

Get the current audio state

To get the current audio state, call getCallAudioState(). getCallAudioState() returns if the device is streaming using Bluetooth, Earpiece, Wired, or Speaker.

mAudioState = connection.getCallAudioState()

On State Changed

Subscribe to changes in CallAudioState by overriding onCallAudioStateChanged(). This alerts you of any changes to the state.

fun onCallAudioStateChanged(audioState: CallAudioState) {
  mAudioState = audioState
}

@Override
public void onCallAudioStateChanged(CallAudioState audioState) {
  mAudioState = audioState;
}

Get the current device

Get the current active device using CallAudioState.getActiveBluetoothDevice(). This function returns the active Bluetooth device.

val activeDevice: BluetoothDevice = mAudioState.getActiveBluetoothDevice()

BluetoothDevice activeDevice = mAudioState.getActiveBluetoothDevice();

Get Bluetooth devices

Get a list of Bluetooth devices that are available for call audio routing using CallAudioState.getSupportedBluetoothDevices().

val availableBluetoothDevices: Collection =
  mAudioState.getSupportedBluetoothDevices()

Collection availableBluetoothDevices = mAudioState.getSupportedBluetoothDevices();

Route the call audio

Using API level 28 and higher (recommended)

Route the call audio to an available Bluetooth device using requestBluetoothAudio(BluetoothDevice):

requestBluetoothAudio(availableBluetoothDevices[0]);

Using API level 23 and higher

Enable ROUTE_BLUETOOTH without specifying the device using setAudioRoute(int). This defaults routing to current, active bluetooth devices on Android 9 and higher.

setAudioRoute(CallAudioState.ROUTE_BLUETOOTH);