Fix/some bugs reported by users (#441)

* Set different rendering methods for web and native.

* Revert a modification that issued an exception.

* Update video_track_renderer.dart

* dart format.

* update.

Author: cloudwebrtc

lib/src/core/engine.dart

@@ -830,11 +830,8 @@ class Engine extends Disposable with EventsEmittable<EngineEvent> {
   }) async {
     final previousAnswer =
         (await subscriber?.pc.getLocalDescription())?.toPBType();
-    final previousOffer =
-        (await publisher?.pc.getLocalDescription())?.toPBType();
     signalClient.sendSyncState(
       answer: previousAnswer,
-      offer: previousOffer,
       subscription: subscription,
       publishTracks: publishTracks,
       dataChannelInfo: dataChannelInfo(),

lib/src/core/signal_client.dart

@@ -523,15 +523,13 @@ extension SignalClientRequests on SignalClient {
   @internal
   void sendSyncState({
     required lk_rtc.SessionDescription? answer,
-    required lk_rtc.SessionDescription? offer,
     required lk_rtc.UpdateSubscription subscription,
     required Iterable<lk_rtc.TrackPublishedResponse>? publishTracks,
     required Iterable<lk_rtc.DataChannelInfo>? dataChannelInfo,
   }) =>
       _sendRequest(lk_rtc.SignalRequest(
         syncState: lk_rtc.SyncState(
           answer: answer,
-          offer: offer,
           subscription: subscription,
           publishTracks: publishTracks,
           dataChannels: dataChannelInfo,

lib/src/widgets/video_track_renderer.dart

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
 import 'package:flutter_webrtc/flutter_webrtc.dart' as rtc;
@@ -52,10 +53,19 @@ class VideoTrackRenderer extends StatefulWidget {
 
 class _VideoTrackRendererState extends State<VideoTrackRenderer> {
   rtc.RTCVideoRenderer? _renderer;
+  // for flutter web only.
+  bool _rendererReadyForWeb = false;
   EventsListener<TrackEvent>? _listener;
   // Used to compute visibility information
   late GlobalKey _internalKey;
 
+  Future<rtc.RTCVideoRenderer> _initializeRenderer() async {
+    _renderer ??= rtc.RTCVideoRenderer();
+    await _renderer!.initialize();
+    await _attach();
+    return _renderer!;
+  }
+
   void disposeRenderer() {
     try {
       _renderer?.srcObject = null;
@@ -70,12 +80,12 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
   void initState() {
     super.initState();
     _internalKey = widget.track.addViewKey();
-    () async {
-      _renderer ??= rtc.RTCVideoRenderer();
-      await _renderer!.initialize();
-      await _attach();
-      setState(() {});
-    }();
+    if (kIsWeb) {
+      () async {
+        await _initializeRenderer();
+        setState(() => _rendererReadyForWeb = true);
+      }();
+    }
   }
 
   @override
@@ -118,9 +128,9 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
     }
   }
 
-  @override
-  Widget build(BuildContext context) => _renderer != null
-      ? Builder(
+  Widget _videoViewForWeb() => !_rendererReadyForWeb
+      ? Container()
+      : Builder(
           key: _internalKey,
           builder: (ctx) {
             // let it render before notifying build
@@ -135,8 +145,37 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
               objectFit: widget.fit,
             );
           },
-        )
-      : Container();
+        );
+
+  Widget _videoViewForNative() => FutureBuilder(
+      future: _initializeRenderer(),
+      builder: (context, snapshot) {
+        if (snapshot.hasData && _renderer != null) {
+          return Builder(
+            key: _internalKey,
+            builder: (ctx) {
+              // let it render before notifying build
+              WidgetsBindingCompatible.instance
+                  ?.addPostFrameCallback((timeStamp) {
+                widget.track.onVideoViewBuild?.call(_internalKey);
+              });
+              return rtc.RTCVideoView(
+                _renderer!,
+                mirror: _shouldMirror(),
+                filterQuality: FilterQuality.medium,
+                objectFit: widget.fit,
+              );
+            },
+          );
+        }
+        return Container();
+      });
+
+  // FutureBuilder will cause flickering for flutter web. so using
+  // different rendering methods for web and native.
+  @override
+  Widget build(BuildContext context) =>
+      kIsWeb ? _videoViewForWeb() : _videoViewForNative();
 
   bool _shouldMirror() {
     // off for screen share