doc: doc how to use RtcEnginePlugin (#482)

README.md

@@ -51,6 +51,14 @@ Open the `Info.plist` and add:
 
 Your application can still run the voice call when it is switched to the background if the background mode is enabled. Select the app target in Xcode, click the **Capabilities** tab, enable **Background Modes**, and check **Audio, AirPlay, and Picture in Picture**.
 
+## Interact with RtcEngine/AgoraRtcEngineKit on Android/iOS
+
+`agora_rtc_engine` has not implemented all the features of agora native (Android/iOS) sdk, due to performance reasons, such as [Custom Audio Source and Renderer](https://docs.agora.io/en/Video/custom_audio_android?platform=Android), [Custom Video Source and Renderer](https://docs.agora.io/en/Video/custom_video_android?platform=Android), [Raw Audio Data](https://docs.agora.io/en/Video/raw_data_audio_android?platform=Android), etc. `agora_rtc_engine` provides [RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt)/[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/ios/Classes/Base/RtcEnginePlugin.h), allowing you to to interact with the [RtcEngine](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/lib/src/rtc_engine.dart) created on the Flutter side in the Android/iOS code, you can implement your own plugin by inheriting [RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt)/[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/ios/Classes/Base/RtcEnginePlugin.h), and get the [RtcEngine](https://docs.agora.io/en/Video/API%20Reference/java/classio_1_1agora_1_1rtc_1_1_rtc_engine.html)/[AgoraRtcEngineKit](https://docs.agora.io/en/Video/API%20Reference/oc/Classes/AgoraRtcEngineKit.html) in the `onRtcEngineCreated` callback. Please note that you should not call the [RtcEngine.destroy](https://docs.agora.io/en/Video/API%20Reference/java/classio_1_1agora_1_1rtc_1_1_rtc_engine.html#afb808cdc9025a77af7dd2bce98311bfe)/[AgoraRtcEngineKit.destroy](https://docs.agora.io/en/Video/API%20Reference/oc/Classes/AgoraRtcEngineKit.html#//api/name/destroy) function on Android/iOS code, because it will affect the [RtcEngine](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/lib/src/rtc_engine.dart) on the Flutter side. To see how to use `RtcEnginePlugin`, please check the custom audio source example:
+
+Android：[CustomAudioPlugin.kt](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/example/android/app/src/main/kotlin/io/agora/agora_rtc_engine_example/custom_audio_source/CustomAudioPlugin.kt)
+
+iOS：[CustmoAudioSourcePlugin.swift](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/example/ios/Runner/CustomAudioSource/CustmoAudioSourcePlugin.swift)
+
 ## Error handling
 
 ### Android build error

README.zh.md

@@ -51,6 +51,14 @@ Agora 视频 SDK 需要 `摄像头` 和 `麦克风` 权限来开始视频通话
 
 您的程序可以在后台运行音视频通话，前提是您开启了后台模式。在 Xcode 中选择您的 app target，点击 **Capabilities** 标签，开启 **Background Modes**，并且检查 **Audio、AirPlay 和 Picture in Picture**。
 
+## 在Android/iOS中与[RtcEngine](https://docs.agora.io/cn/Video/API%20Reference/java/classio_1_1agora_1_1rtc_1_1_rtc_engine.html)/[AgoraRtcEngineKit](https://docs.agora.io/cn/Video/API%20Reference/oc/Classes/AgoraRtcEngineKit.html)交互
+
+由于性能原因，`agora_rtc_engine`暂时没有实现agora native(Android/iOS) sdk的所有功能，如[自定义音频采集和渲染](hhttps://docs.agora.io/cn/Video/custom_audio_android?platform=Android)，[自定义视频采集和渲染](https://docs.agora.io/cn/Video/custom_video_android?platform=Android)，[原始音频数据](https://docs.agora.io/cn/Video/raw_data_audio_android?platform=Android)等功能，`agora_rtc_engine`提供[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt)/[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/ios/Classes/Base/RtcEnginePlugin.h)，允许你在Android/iOS代码中与Flutter端创建的[RtcEngine](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/lib/src/rtc_engine.dart)交互，你可以继承[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt)/[RtcEnginePlugin](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/ios/Classes/Base/RtcEnginePlugin.h)实现自己的插件，在`onRtcEngineCreated`回调中获取[RtcEngine](https://docs.agora.io/cn/Video/API%20Reference/java/classio_1_1agora_1_1rtc_1_1_rtc_engine.html)/[AgoraRtcEngineKit](https://docs.agora.io/cn/Video/API%20Reference/oc/Classes/AgoraRtcEngineKit.html)，请注意不要在Android/iOS中调用[RtcEngine.destroy](https://docs.agora.io/cn/Video/API%20Reference/java/classio_1_1agora_1_1rtc_1_1_rtc_engine.html#afb808cdc9025a77af7dd2bce98311bfe)/[AgoraRtcEngineKit.destroy](https://docs.agora.io/cn/Video/API%20Reference/oc/Classes/AgoraRtcEngineKit.html#//api/name/destroy)方法，因为这会影响Flutter端的[RtcEngine](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/lib/src/rtc_engine.dart)功能。如何使用`RtcEnginePlugin`，请查看我们提供的音频自采集demo:
+
+Android：[CustomAudioPlugin.kt](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/example/android/app/src/main/kotlin/io/agora/agora_rtc_engine_example/custom_audio_source/CustomAudioPlugin.kt)
+
+iOS：[CustmoAudioSourcePlugin.swift](https://github.com/AgoraIO/Agora-Flutter-SDK/blob/master/example/ios/Runner/CustomAudioSource/CustmoAudioSourcePlugin.swift)
+
 ## 常见问题
 
 ### iOS 无法显示视频（Android 是好的）

android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt

@@ -12,6 +12,9 @@ interface RtcEnginePlugin {
    * This callback will be called when the [RtcEngine] is created by
    * [RtcEngine.createWithContext](https://docs.agora.io/cn/Video/API%20Reference/flutter/agora_rtc_engine/RtcEngine/createWithContext.html)
    * function from flutter.
+   *   
+   * NOTE that you should not call [RtcEngine.destroy], because it will also destroy the `RtcEngine` 
+   * used by flutter side.
    *
    * @param rtcEngine The same [RtcEngine] used by flutter side
    */

ios/Classes/Base/RtcEnginePlugin.h

@@ -13,8 +13,11 @@ NS_ASSUME_NONNULL_BEGIN
  * This callback will be called when the `RtcEngine` is created by
  [RtcEngine.createWithContext](https://docs.agora.io/cn/Video/API%20Reference/flutter/agora_rtc_engine/RtcEngine/createWithContext.html)
  * function from flutter.
+
+ * NOTE that you should not call `AgoraRtcEngineKit.destroy`, because it will also destroy the `RtcEngine` 
+ * used by flutter side.
  *
- * @param rtcEngine The same [RtcEngine] used by flutter side
+ * @param rtcEngine The same `AgoraRtcEngineKit` used by flutter side
  */
 - (void)onRtcEngineCreated:(AgoraRtcEngineKit *_Nullable)rtcEngine;