如何在后台使用Flutter Method Channel（应用最小/关闭） [英] How to use Flutter Method Channel in background (app minimised/closed)

问题描述

我正在使用Flutter应用程序中的本机Android小部件。其中有刷新按钮，单击后必须在Flutter代码中调用一个方法。我正在使用Flutter Method Channel进行通信，当应用程序处于前台时，它工作正常。但是，当应用程序最小化或关闭时，它不起作用。我收到错误 PlatformException（NO_ACTIVITY，null，null）。以下是我的代码。

I am working on a native Android widget in a Flutter App. In which there is refresh button, on click of that I have to call a method in the Flutter code. I am using Flutter Method Channel for the communication and it is working fine when app is in foreground. But it does not work when app is minimised or closed. I get error PlatformException(NO_ACTIVITY, null, null). Below is my code.

Android（AppWidgetProvider）

Android (AppWidgetProvider)

if (methodChannel == null && context != null) {
        FlutterMain.startInitialization(context)
        FlutterMain.ensureInitializationComplete(context, arrayOf())

        // Instantiate a FlutterEngine.
        val engine = FlutterEngine(context.applicationContext)

        // Define a DartEntrypoint
        val entrypoint: DartEntrypoint = DartEntrypoint.createDefault()

        // Execute the DartEntrypoint within the FlutterEngine.
        engine.dartExecutor.executeDartEntrypoint(entrypoint)

        // Register Plugins when in background. When there
        // is already an engine running, this will be ignored (although there will be some
        // warnings in the log).
        //GeneratedPluginRegistrant.registerWith(engine)

        methodChannel = MethodChannel(engine.dartExecutor.binaryMessenger, MainActivity.CHANNEL)
}

methodChannel!!.invokeMethod("fetchNewData", "", object : MethodChannel.Result {
        override fun notImplemented() {
            Toast.makeText(context, "method not implemented", Toast.LENGTH_SHORT).show()
        }

        override fun error(errorCode: String?, errorMessage: String?, errorDetails: Any?) {
            Toast.makeText(context, errorMessage, Toast.LENGTH_SHORT).show()
        }

        override fun success(result: Any?) {
            Toast.makeText(context, "success", Toast.LENGTH_SHORT).show()
        }
})

Flutter

/// calling in main
static Future<void> attachListeners() async {
    WidgetsFlutterBinding.ensureInitialized();
    var bloc = new AqiCnDashboardBloc();
    _channel.setMethodCallHandler((call) {
      switch (call.method) {
        case 'fetchNewData':
          bloc.getAqiCn(false);
          return null;
        default:
          throw MissingPluginException('notImplemented');
      }
    });
}

推荐答案

我正在收集信息/讨论

void callbackDispatcher() {
WidgetsFlutterBinding.ensureInitialized();
print("Our background job ran!");

}

void main() {

 static const MethodChannel _channel = const MethodChannel("channel-name");

 Future<void> initialize(final Function callbackDispatcher) async {

  final callback = PluginUtilities.getCallbackHandle(callbackDispatcher);

 await _channel.invokeMethod('initialize', callback.toRawHandle());
 }
}

如此处所述如何在后台运行Flutter？

启动后台作业时本机Flutter引擎未激活。因此，我们无法运行Dart。
Android / iOS可以在后台启动Flutter引擎吗？
是的！我们首先需要注册Dart回调函数，该函数仅在本机代码启动后台作业时才会调用。
此回调函数称为callbackDispatcher。

When a background job is started by native the Flutter engine is not active. So we are unable to run Dart. Can Android/iOS starts the Flutter engine in the background? Yes! We’ll first need to register a Dart callback function which will only be invoked whenever a background job is started by the native code. This callback function is referred to as a callbackDispatcher.

也请查看这些stackoverflow讨论。

Also please check out these stackoverflow discussions.

Flutter：将应用程序作为后台服务运行

如何在Flutter中创建服务以使应用始终在后台运行？

如何创建Flutter后台服务，该应用程序在应用程序关闭时也可以使用

使用Flutter插件和地理围栏在后台执行Dart

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