docs: update readme for background call handling on ios (#170)

Author: davidliu

README.md

@@ -382,7 +382,11 @@ connection while in the background. The example uses
 [react-native-callkeep](https://github.com/react-native-webrtc/react-native-callkeep)
 for simple integration with CallKit.
 
-Our example code can be found [here](https://github.com/livekit/client-sdk-react-native/blob/main/example/src/callservice/CallService.android.ts).
+Our example code can be found [here](https://github.com/livekit/client-sdk-react-native/blob/main/example/src/callservice/CallService.ios.ts).
+
+For apps planning to use CallKit to handle incoming calls in the background, [it is important to call
+`RTCAudioSession.audioSessionDidActivate/Deactivate` when the call provider activates/deactivates
+the audio session.](https://github.com/livekit/react-native-webrtc/blob/master/Documentation/iOSInstallation.md#callkit)
 
 ## Troubleshooting
 

example/src/callservice/CallService.ios.ts

@@ -5,6 +5,8 @@ import RNCallKeep, {
   AudioSessionMode,
 } from 'react-native-callkeep';
 
+import { RTCAudioSession } from '@livekit/react-native-webrtc';
+
 let uuid = '1932b99c-4fe1-4bf4-897f-763bc4dc21c2';
 
 // This keeps the app alive in the background.
@@ -50,5 +52,13 @@ export function setupCallService() {
     },
   };
   RNCallKeep.setSettings(options);
-  RNCallKeep.addEventListener('didChangeAudioRoute', () => {});
+  RNCallKeep.addEventListener('didChangeAudioRoute', () => {}); // To quell warnings.
+
+  // For apps handling incoming calls from the background.
+  RNCallKeep.addEventListener('didActivateAudioSession', () => {
+    RTCAudioSession.audioSessionDidActivate();
+  });
+  RNCallKeep.addEventListener('didDeactivateAudioSession', () => {
+    RTCAudioSession.audioSessionDidDeactivate();
+  });
 }