feat: 目标不在线时进行提示和更新UI

webrtc_controller_flutter/lib/main.dart

@@ -99,6 +99,9 @@ class _ControllerHomeState extends State<ControllerHome> {
     _controller!.onIceDisconnected = (message) {
       _onIceDisconnected(message);
     };
+    _controller!.onTargetOffline = (message) {
+      _onTargetOffline(message);
+    };
     _controller!.onRemoteStream = (renderer) {
       setState(() => _renderer = renderer);
       renderer.addListener(_onRendererUpdate);
@@ -130,6 +133,20 @@ class _ControllerHomeState extends State<ControllerHome> {
     await _disconnect();
   }
 
+  /// 目标被控端不在线：提示用户并复位到连接设置面板。
+  Future<void> _onTargetOffline(String message) async {
+    final scaffoldCtx = _scaffoldKey.currentState?.context;
+    if (mounted && scaffoldCtx != null) {
+      ScaffoldMessenger.of(scaffoldCtx).showSnackBar(
+        SnackBar(
+          content: Text(message),
+          duration: const Duration(seconds: 3),
+        ),
+      );
+    }
+    setState(() => _connected = false);
+  }
+
   Future<void> _disconnect() async {
     await _controller?.disconnect();
     _controller = null;