diff --git a/example/lib/config/agora.config.dart b/example/lib/config/agora.config.dart
index 945487a81..05251467b 100644
--- a/example/lib/config/agora.config.dart
+++ b/example/lib/config/agora.config.dart
@@ -4,6 +4,11 @@ const appId = YOUR_APP_ID;
 /// Please refer to https://docs.agora.io/en/Agora%20Platform/token
 const token = YOUR_TOEKN;
 
+/// Your channel ID
 const channelId = YOUR_CHANNEL_ID;
+
+/// Your int user ID
 const uid = YOUR_UID;
+
+/// Your string user ID
 const stringUid = YOUR_STRING_UID;
diff --git a/example/lib/examples/advanced/index.dart b/example/lib/examples/advanced/index.dart
index f9dbc5175..6f8a58df0 100644
--- a/example/lib/examples/advanced/index.dart
+++ b/example/lib/examples/advanced/index.dart
@@ -1,5 +1,6 @@
 import 'package:agora_rtc_engine_example/examples/advanced/multi_channel.dart';
 
+/// Data source for advanced examples
 final Advanced = [
   {'name': 'Advanced'},
   {'name': 'MultiChannel', 'widget': MultiChannel()}
diff --git a/example/lib/examples/advanced/multi_channel.dart b/example/lib/examples/advanced/multi_channel.dart
index c05a43166..4171029d1 100644
--- a/example/lib/examples/advanced/multi_channel.dart
+++ b/example/lib/examples/advanced/multi_channel.dart
@@ -10,8 +10,8 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:permission_handler/permission_handler.dart';
 
-const channelId0 = 'channel0';
-const channelId1 = 'channel1';
+const _channelId0 = 'channel0';
+const _channelId1 = 'channel1';
 
 /// MultiChannel Example
 class MultiChannel extends StatefulWidget {
@@ -54,7 +54,7 @@ class _State extends State<MultiChannel> {
       await [Permission.microphone, Permission.camera].request();
     }
 
-    widget._channel0 = await RtcChannel.create(channelId0);
+    widget._channel0 = await RtcChannel.create(_channelId0);
     this._addListener(widget._channel0);
 
     await widget._channel0.setClientRole(ClientRole.Broadcaster);
@@ -67,7 +67,7 @@ class _State extends State<MultiChannel> {
       await [Permission.microphone, Permission.camera].request();
     }
 
-    widget._channel1 = await RtcChannel.create(channelId1);
+    widget._channel1 = await RtcChannel.create(_channelId1);
     this._addListener(widget._channel1);
 
     await widget._channel1.setClientRole(ClientRole.Broadcaster);
@@ -80,11 +80,11 @@ class _State extends State<MultiChannel> {
     channel.setEventHandler(
         RtcChannelEventHandler(joinChannelSuccess: (channel, uid, elapsed) {
       log('joinChannelSuccess ${channel} ${uid} ${elapsed}');
-      if (channelId == channelId0) {
+      if (channelId == _channelId0) {
         setState(() {
           isJoined0 = true;
         });
-      } else if (channelId == channelId1) {
+      } else if (channelId == _channelId1) {
         setState(() {
           isJoined1 = true;
         });
@@ -95,12 +95,12 @@ class _State extends State<MultiChannel> {
       log('userOffline ${channel.channelId} $uid $reason');
     }, leaveChannel: (stats) {
       log('leaveChannel ${channel.channelId} ${stats.toJson()}');
-      if (channelId == channelId0) {
+      if (channelId == _channelId0) {
         this.setState(() {
           isJoined0 = false;
           remoteUid0.clear();
         });
-      } else if (channelId == channelId1) {
+      } else if (channelId == _channelId1) {
         this.setState(() {
           isJoined1 = false;
           remoteUid1.clear();
@@ -109,21 +109,21 @@ class _State extends State<MultiChannel> {
     }, remoteVideoStateChanged: (uid, state, reason, elapsed) {
       log('remoteVideoStateChanged ${uid} ${state} ${reason} ${elapsed}');
       if (state == VideoRemoteState.Starting) {
-        if (channelId == channelId0) {
+        if (channelId == _channelId0) {
           this.setState(() {
             remoteUid0.add(uid);
           });
-        } else if (channelId == channelId1) {
+        } else if (channelId == _channelId1) {
           this.setState(() {
             remoteUid1.add(uid);
           });
         }
       } else if (state == VideoRemoteState.Stopped) {
-        if (channelId == channelId0) {
+        if (channelId == _channelId0) {
           this.setState(() {
             remoteUid0.removeWhere((element) => element == uid);
           });
-        } else if (channelId == channelId1) {
+        } else if (channelId == _channelId1) {
           this.setState(() {
             remoteUid1.removeWhere((element) => element == uid);
           });
@@ -168,7 +168,7 @@ class _State extends State<MultiChannel> {
                         this._joinChannel0();
                       }
                     },
-                    child: Text('${isJoined0 ? 'Leave' : 'Join'} $channelId0'),
+                    child: Text('${isJoined0 ? 'Leave' : 'Join'} $_channelId0'),
                   ),
                 )
               ],
@@ -185,7 +185,7 @@ class _State extends State<MultiChannel> {
                         this._joinChannel1();
                       }
                     },
-                    child: Text('${isJoined1 ? 'Leave' : 'Join'} $channelId1'),
+                    child: Text('${isJoined1 ? 'Leave' : 'Join'} $_channelId1'),
                   ),
                 )
               ],
@@ -200,27 +200,27 @@ class _State extends State<MultiChannel> {
             children: [
               RaisedButton(
                 onPressed: this._publishChannel0,
-                child: Text('Publish ${channelId0}'),
+                child: Text('Publish ${_channelId0}'),
               ),
               RaisedButton(
                 onPressed: () {
                   setState(() {
-                    renderChannelId = channelId0;
+                    renderChannelId = _channelId0;
                   });
                 },
-                child: Text('Render ${channelId0}'),
+                child: Text('Render ${_channelId0}'),
               ),
               RaisedButton(
                 onPressed: this._publishChannel1,
-                child: Text('Publish ${channelId1}'),
+                child: Text('Publish ${_channelId1}'),
               ),
               RaisedButton(
                 onPressed: () {
                   setState(() {
-                    renderChannelId = channelId1;
+                    renderChannelId = _channelId1;
                   });
                 },
-                child: Text('Render ${channelId1}'),
+                child: Text('Render ${_channelId1}'),
               ),
             ],
           ),
@@ -231,9 +231,9 @@ class _State extends State<MultiChannel> {
 
   _renderVideo() {
     List<int> remoteUid = null;
-    if (renderChannelId == channelId0) {
+    if (renderChannelId == _channelId0) {
       remoteUid = remoteUid0;
-    } else if (renderChannelId == channelId1) {
+    } else if (renderChannelId == _channelId1) {
       remoteUid = remoteUid1;
     }
     return Expanded(
diff --git a/example/lib/examples/basic/index.dart b/example/lib/examples/basic/index.dart
index 7e3fbc9d5..3db05577a 100644
--- a/example/lib/examples/basic/index.dart
+++ b/example/lib/examples/basic/index.dart
@@ -2,6 +2,7 @@ import 'package:agora_rtc_engine_example/examples/basic/join_channel_audio.dart'
 import 'package:agora_rtc_engine_example/examples/basic/join_channel_video.dart';
 import 'package:agora_rtc_engine_example/examples/basic/string_uid.dart';
 
+/// Data source for basic examples
 final Basic = [
   {'name': 'Basic'},
   {'name': 'JoinChannelAudio', 'widget': JoinChannelAudio()},
diff --git a/example/lib/examples/basic/join_channel_video.dart b/example/lib/examples/basic/join_channel_video.dart
index dbd0e49a9..068cac6d9 100644
--- a/example/lib/examples/basic/join_channel_video.dart
+++ b/example/lib/examples/basic/join_channel_video.dart
@@ -157,27 +157,26 @@ class _State extends State<JoinChannelVideo> {
       child: Stack(
         children: [
           RtcLocalView.SurfaceView(),
-          if (remoteUid != null)
-            Align(
-              alignment: Alignment.topLeft,
-              child: SingleChildScrollView(
-                scrollDirection: Axis.horizontal,
-                child: Row(
-                  children: List.of(remoteUid.map(
-                    (e) => GestureDetector(
-                      onTap: this._switchRender,
-                      child: Container(
-                        width: 120,
-                        height: 120,
-                        child: RtcRemoteView.SurfaceView(
-                          uid: e,
-                        ),
+          Align(
+            alignment: Alignment.topLeft,
+            child: SingleChildScrollView(
+              scrollDirection: Axis.horizontal,
+              child: Row(
+                children: List.of(remoteUid.map(
+                  (e) => GestureDetector(
+                    onTap: this._switchRender,
+                    child: Container(
+                      width: 120,
+                      height: 120,
+                      child: RtcRemoteView.SurfaceView(
+                        uid: e,
                       ),
                     ),
-                  )),
-                ),
+                  ),
+                )),
               ),
-            )
+            ),
+          )
         ],
       ),
     );
diff --git a/lib/agora_rtc_engine_web.dart b/lib/agora_rtc_engine_web.dart
index f2b9604b0..59939e20d 100644
--- a/lib/agora_rtc_engine_web.dart
+++ b/lib/agora_rtc_engine_web.dart
@@ -1,4 +1,5 @@
 import 'dart:async';
+
 // In order to *not* need this ignore, consider extracting the "web" version
 // of your plugin as a separate package, instead of inlining it in the same
 // package as the core of your plugin.
@@ -11,7 +12,7 @@ import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 /// A web implementation of the AgoraRtcEngine plugin.
 class AgoraRtcEngineWeb {
   static void registerWith(Registrar registrar) {
-    final MethodChannel channel = MethodChannel(
+    final channel = MethodChannel(
       'agora_rtc_engine',
       const StandardMethodCodec(),
       registrar.messenger,
@@ -28,11 +29,11 @@ class AgoraRtcEngineWeb {
     switch (call.method) {
       case 'getPlatformVersion':
         return getPlatformVersion();
-        break;
       default:
         throw PlatformException(
           code: 'Unimplemented',
-          details: 'agora_rtc_engine for web doesn\'t implement \'${call.method}\'',
+          details:
+              'agora_rtc_engine for web doesn\'t implement \'${call.method}\'',
         );
     }
   }
diff --git a/lib/rtc_channel.dart b/lib/rtc_channel.dart
index c89b8681b..256fcb38f 100644
--- a/lib/rtc_channel.dart
+++ b/lib/rtc_channel.dart
@@ -1,2 +1,2 @@
-export 'src/events.dart' show RtcChannelEventHandler;
+export 'src/events.dart' hide RtcEngineEventHandler;
 export 'src/rtc_channel.dart' show RtcChannel;
diff --git a/lib/rtc_engine.dart b/lib/rtc_engine.dart
index 8919aefe4..fdf09d846 100644
--- a/lib/rtc_engine.dart
+++ b/lib/rtc_engine.dart
@@ -1,5 +1,5 @@
 export 'src/classes.dart';
 export 'src/enums.dart';
-export 'src/events.dart' show RtcEngineEventHandler;
+export 'src/events.dart' hide RtcChannelEventHandler;
 export 'src/rtc_engine.dart' show RtcEngine;
 export 'src/rtc_engine_extension.dart';
diff --git a/lib/src/events.dart b/lib/src/events.dart
index 203945008..050f6edd7 100644
--- a/lib/src/events.dart
+++ b/lib/src/events.dart
@@ -2,96 +2,153 @@ import 'classes.dart';
 import 'enum_converter.dart';
 import 'enums.dart';
 
+// ignore: public_member_api_docs
 typedef EmptyCallback = void Function();
+// ignore: public_member_api_docs
 typedef WarningCallback = void Function(WarningCode warn);
+// ignore: public_member_api_docs
 typedef ErrorCallback = void Function(ErrorCode err);
+// ignore: public_member_api_docs
 typedef ApiCallCallback = void Function(
     ErrorCode error, String api, String result);
+// ignore: public_member_api_docs
 typedef UidWithElapsedAndChannelCallback = void Function(
     String channel, int uid, int elapsed);
+// ignore: public_member_api_docs
 typedef RtcStatsCallback = void Function(RtcStats stats);
+// ignore: public_member_api_docs
 typedef UserAccountCallback = void Function(int uid, String userAccount);
+// ignore: public_member_api_docs
 typedef UserInfoCallback = void Function(int uid, UserInfo userInfo);
+// ignore: public_member_api_docs
 typedef ClientRoleCallback = void Function(
     ClientRole oldRole, ClientRole newRole);
+// ignore: public_member_api_docs
 typedef UidWithElapsedCallback = void Function(int uid, int elapsed);
+// ignore: public_member_api_docs
 typedef UserOfflineCallback = void Function(int uid, UserOfflineReason reason);
+// ignore: public_member_api_docs
 typedef ConnectionStateCallback = void Function(
     ConnectionStateType state, ConnectionChangedReason reason);
+// ignore: public_member_api_docs
 typedef NetworkTypeCallback = void Function(NetworkType type);
+// ignore: public_member_api_docs
 typedef TokenCallback = void Function(String token);
+// ignore: public_member_api_docs
 typedef AudioVolumeCallback = void Function(
     List<AudioVolumeInfo> speakers, int totalVolume);
+// ignore: public_member_api_docs
 typedef UidCallback = void Function(int uid);
+// ignore: public_member_api_docs
 typedef ElapsedCallback = void Function(int elapsed);
+// ignore: public_member_api_docs
 typedef VideoFrameCallback = void Function(int width, int height, int elapsed);
+// ignore: public_member_api_docs
 typedef UidWithMutedCallback = void Function(int uid, bool muted);
+// ignore: public_member_api_docs
 typedef VideoSizeCallback = void Function(
     int uid, int width, int height, int rotation);
+// ignore: public_member_api_docs
 typedef RemoteVideoStateCallback = void Function(int uid,
     VideoRemoteState state, VideoRemoteStateReason reason, int elapsed);
+// ignore: public_member_api_docs
 typedef LocalVideoStateCallback = void Function(
     LocalVideoStreamState localVideoState, LocalVideoStreamError error);
+// ignore: public_member_api_docs
 typedef RemoteAudioStateCallback = void Function(int uid,
     AudioRemoteState state, AudioRemoteStateReason reason, int elapsed);
+// ignore: public_member_api_docs
 typedef LocalAudioStateCallback = void Function(
     AudioLocalState state, AudioLocalError error);
+// ignore: public_member_api_docs
 typedef FallbackCallback = void Function(bool isFallbackOrRecover);
+// ignore: public_member_api_docs
 typedef FallbackWithUidCallback = void Function(
     int uid, bool isFallbackOrRecover);
+// ignore: public_member_api_docs
 typedef AudioRouteCallback = void Function(AudioOutputRouting routing);
+// ignore: public_member_api_docs
 typedef RectCallback = void Function(Rect rect);
+// ignore: public_member_api_docs
 typedef NetworkQualityCallback = void Function(NetworkQuality quality);
+// ignore: public_member_api_docs
 typedef NetworkQualityWithUidCallback = void Function(
     int uid, NetworkQuality txQuality, NetworkQuality rxQuality);
+// ignore: public_member_api_docs
 typedef LastmileProbeCallback = void Function(LastmileProbeResult result);
+// ignore: public_member_api_docs
 typedef LocalVideoStatsCallback = void Function(LocalVideoStats stats);
+// ignore: public_member_api_docs
 typedef LocalAudioStatsCallback = void Function(LocalAudioStats stats);
+// ignore: public_member_api_docs
 typedef RemoteVideoStatsCallback = void Function(RemoteVideoStats stats);
+// ignore: public_member_api_docs
 typedef RemoteAudioStatsCallback = void Function(RemoteAudioStats stats);
+// ignore: public_member_api_docs
 typedef AudioMixingStateCallback = void Function(
     AudioMixingStateCode state, AudioMixingErrorCode errorCode);
+// ignore: public_member_api_docs
 typedef SoundIdCallback = void Function(int soundId);
+// ignore: public_member_api_docs
 typedef RtmpStreamingStateCallback = void Function(
     String url, RtmpStreamingState state, RtmpStreamingErrorCode errCode);
+// ignore: public_member_api_docs
 typedef StreamInjectedStatusCallback = void Function(
     String url, int uid, InjectStreamStatus status);
+// ignore: public_member_api_docs
 typedef StreamMessageCallback = void Function(
     int uid, int streamId, String data);
+// ignore: public_member_api_docs
 typedef StreamMessageErrorCallback = void Function(
     int uid, int streamId, ErrorCode error, int missed, int cached);
+// ignore: public_member_api_docs
 typedef MediaRelayStateCallback = void Function(
     ChannelMediaRelayState state, ChannelMediaRelayError code);
+// ignore: public_member_api_docs
 typedef MediaRelayEventCallback = void Function(ChannelMediaRelayEvent code);
+// ignore: public_member_api_docs
 typedef VideoFrameWithUidCallback = void Function(
     int uid, int width, int height, int elapsed);
+// ignore: public_member_api_docs
 typedef UrlWithErrorCallback = void Function(String url, ErrorCode error);
+// ignore: public_member_api_docs
 typedef UrlCallback = void Function(String url);
+// ignore: public_member_api_docs
 typedef TransportStatsCallback = void Function(
     int uid, int delay, int lost, int rxKBitRate);
+// ignore: public_member_api_docs
 typedef UidWithEnabledCallback = void Function(int uid, bool enabled);
+// ignore: public_member_api_docs
 typedef EnabledCallback = void Function(bool enabled);
+// ignore: public_member_api_docs
 typedef AudioQualityCallback = void Function(
     int uid, int quality, int delay, int lost);
+// ignore: public_member_api_docs
 typedef MetadataCallback = void Function(
     String buffer, int uid, int timeStampMs);
+// ignore: public_member_api_docs
 typedef FacePositionCallback = void Function(
     int imageWidth, int imageHeight, List<FacePositionInfo> faces);
+// ignore: public_member_api_docs
 typedef StreamPublishStateCallback = void Function(
     String channel,
     StreamPublishState oldState,
     StreamPublishState newState,
     int elapseSinceLastState);
+// ignore: public_member_api_docs
 typedef StreamSubscribeStateCallback = void Function(
     String channel,
     int uid,
     StreamSubscribeState oldState,
     StreamSubscribeState newState,
     int elapseSinceLastState);
+// ignore: public_member_api_docs
 typedef RtmpStreamingEventCallback = void Function(
     String url, RtmpStreamingEvent eventCode);
+// ignore: public_member_api_docs
 typedef UserSuperResolutionEnabledCallback = void Function(
     int uid, bool enabled, SuperResolutionStateReason reason);
+// ignore: public_member_api_docs
 typedef UploadLogResultCallback = void Function(
     String requestId, bool success, UploadErrorReason reason);
 
@@ -881,8 +938,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the first audio frame is published.
   ///
-  ///
-  ///
   /// The SDK triggers this callback under one of the following circumstances:
   /// - The local client enables the audio module and calls [RtcEngine.joinChannel] successfully.
   /// - The local client calls [RtcEngine.muteLocalAudioStream] (`true`) and [RtcEngine.muteLocalAudioStream] (`false`) in sequence.
@@ -894,8 +949,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the first video frame is published.
   ///
-  ///
-  ///
   /// The SDK triggers this callback under one of the following circumstances:
   /// - The local client enables the video module and calls [RtcEngine.joinChannel] successfully.
   /// - The local client calls [RtcEngine.muteLocalVideoStream] (`true`) and [RtcEngine.muteLocalVideoStream] (`false`) in sequence.
@@ -907,8 +960,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the audio publishing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the publishing state change of the local audio stream.
   ///
   /// The `StreamPublishStateCallback` typedef includes the following parameters:
@@ -920,8 +971,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the video publishing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the publishing state change of the local video stream.
   ///
   /// The `StreamPublishStateCallback` typedef includes the following parameters:
@@ -933,8 +982,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the audio subscribing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the subscribing state change of a remote audio stream.
   ///
   /// The `StreamSubscribeStateCallback` typedef includes the following parameters:
@@ -946,8 +993,6 @@ class RtcEngineEventHandler {
 
   /// Occurs when the video subscribing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the subscribing state change of a remote video stream.
   ///
   /// The `StreamSubscribeStateCallback` typedef includes the following parameters:
@@ -959,8 +1004,6 @@ class RtcEngineEventHandler {
 
   /// Reports events during the RTMP or RTMPS streaming.
   ///
-  ///
-  ///
   /// The `RtmpStreamingEventCallback` typedef includes the following parameters:
   /// - [String] `url`: The RTMP or RTMPS streaming URL.
   /// - [RtmpStreamingEvent] `eventCode`: The event code. See [RtmpStreamingEvent].
@@ -1688,8 +1731,6 @@ class RtcChannelEventHandler {
 
   /// Occurs when the audio publishing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the publishing state change of the local audio stream.
   ///
   /// The `StreamPublishStateCallback` typedef includes the following parameters:
@@ -1701,8 +1742,6 @@ class RtcChannelEventHandler {
 
   /// Occurs when the video publishing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the publishing state change of the local video stream.
   ///
   /// The `StreamPublishStateCallback` typedef includes the following parameters:
@@ -1714,8 +1753,6 @@ class RtcChannelEventHandler {
 
   /// Occurs when the audio subscribing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the subscribing state change of a remote audio stream.
   ///
   /// The `StreamSubscribeStateCallback` typedef includes the following parameters:
@@ -1727,8 +1764,6 @@ class RtcChannelEventHandler {
 
   /// Occurs when the video subscribing state changes.
   ///
-  ///
-  ///
   /// This callback indicates the subscribing state change of a remote video stream.
   ///
   /// The `StreamSubscribeStateCallback` typedef includes the following parameters:
@@ -1740,8 +1775,6 @@ class RtcChannelEventHandler {
 
   /// Reports events during the RTMP or RTMPS streaming.
   ///
-  ///
-  ///
   /// The `RtmpStreamingEventCallback` typedef includes the following parameters:
   /// - [String] `url`: The RTMP or RTMPS streaming URL.
   /// - [RtmpStreamingEvent] `eventCode`: The event code. See [RtmpStreamingEvent].
diff --git a/lib/src/rtc_engine.dart b/lib/src/rtc_engine.dart
index 4542ed7d8..8678fd4fb 100644
--- a/lib/src/rtc_engine.dart
+++ b/lib/src/rtc_engine.dart
@@ -68,10 +68,6 @@ class RtcEngine with RtcEngineInterface {
 
   /// Creates an [RtcEngine] instance.
   ///
-  /// **Deprecated**
-  ///
-  /// This method is deprecated since v3.3.1.
-  ///
   /// Unless otherwise specified, all the methods provided by the RtcEngine class are executed asynchronously. Agora recommends calling these methods in the same thread.
   ///
   /// **Note**
@@ -117,8 +113,7 @@ class RtcEngine with RtcEngineInterface {
   /// - The error code, if this method call fails:
   ///   - [ErrorCode.InvalidAppId]
   @deprecated
-  static Future<RtcEngine> createWithAreaCode(
-      String appId, AreaCode areaCode) async {
+  static Future<RtcEngine> createWithAreaCode(String appId, AreaCode areaCode) {
     return createWithConfig(RtcEngineConfig(appId, areaCode: areaCode));
   }
 
diff --git a/test/agora_rtc_engine_test.dart b/test/agora_rtc_engine_test.dart
index 51e4ffebf..a8582a269 100644
--- a/test/agora_rtc_engine_test.dart
+++ b/test/agora_rtc_engine_test.dart
@@ -4,7 +4,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  const MethodChannel channel = MethodChannel('agora_rtc_engine');
+  const channel = MethodChannel('agora_rtc_engine');
 
   TestWidgetsFlutterBinding.ensureInitialized();