fix(android): prevent screen from turning off during active video calls in example application (#1057)

This PR fixes an issue in the Android example application where the
device screen turns off automatically during an active video call due to
screen timeout.

### **Problem**
During an ongoing LiveKit call on Android, the screen is not kept awake,
which leads to:

- Poor user experience during video calls
- Interrupted visibility when no user interaction occurs

### **Solution**
This PR adds native Android window flag handling in MainActivity to
ensure the screen remains active while a call is in progress:

- Uses native flags to prevent screen timeout
- Uses native flags as well to handle lock screen visibility

### **The flags are:**
- **Enabled** when the room is active
- **Cleared** when the room is disposed

---------

Co-authored-by: Hiroshi Horie <548776+hiroshihorie@users.noreply.github.com>

Author: mechtech-mind

example/android/app/src/main/kotlin/io/livekit/example/MainActivity.kt

@@ -1,6 +1,48 @@
 package io.livekit.example
 
+import android.os.Build
+import android.os.Bundle
+import android.view.WindowManager
 import io.flutter.embedding.android.FlutterActivity
+import io.flutter.embedding.engine.FlutterEngine
+import io.flutter.plugin.common.MethodChannel
 
-class MainActivity: FlutterActivity() {
-}
+class MainActivity : FlutterActivity() {
+
+    private val CHANNEL = "livekit_incall"
+
+    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
+        super.configureFlutterEngine(flutterEngine)
+
+        MethodChannel(
+            flutterEngine.dartExecutor.binaryMessenger,
+            CHANNEL
+        ).setMethodCallHandler { call, result ->
+            when (call.method) {
+                "enableInCall" -> {
+                    setInCallScreenFlags()
+                    result.success(null)
+                }
+                "disableInCall" -> {
+                    clearInCallScreenFlags()
+                    result.success(null)
+                }
+                else -> result.notImplemented()
+            }
+        }
+    }
+
+    private fun setInCallScreenFlags() {
+        val window = window
+
+        // Keep screen on during call
+        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+    }
+
+    private fun clearInCallScreenFlags() {
+        val window = window
+
+        // Remove keep screen on
+        window.clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+    }
+}

example/lib/pages/room.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 import 'dart:math' as math;
 
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:livekit_client/livekit_client.dart';
 
 import '../exts.dart';
@@ -34,6 +35,11 @@ class _RoomPageState extends State<RoomPage> {
   @override
   void initState() {
     super.initState();
+
+    if (lkPlatformIs(PlatformType.android)) {
+      unawaited(enableInCallFlags());
+    }
+
     // add callback for a `RoomEvent` as opposed to a `ParticipantEvent`
     widget.room.addListener(_onRoomDidUpdate);
     // add callbacks for finer grained events
@@ -63,6 +69,9 @@ class _RoomPageState extends State<RoomPage> {
     widget.room.removeListener(_onRoomDidUpdate);
     unawaited(_disposeRoomAsync());
     onWindowShouldClose = null;
+    if (lkPlatformIs(PlatformType.android)) {
+      unawaited(disableInCallFlags());
+    }
     super.dispose();
   }
 
@@ -71,6 +80,16 @@ class _RoomPageState extends State<RoomPage> {
     await widget.room.dispose();
   }
 
+  static const platform = MethodChannel('livekit_incall');
+
+  Future<void> enableInCallFlags() async {
+    await platform.invokeMethod('enableInCall');
+  }
+
+  Future<void> disableInCallFlags() async {
+    await platform.invokeMethod('disableInCall');
+  }
+
   /// for more information, see [event types](https://docs.livekit.io/client/events/#events)
   void _setUpListeners() => _listener
     ..on<RoomDisconnectedEvent>((event) async {