我的MainActivity.kt：

class MainActivity : FlutterActivity() {

    private val CHANNEL = "flutter.native/helper"
    private var mapId: Int? = null

    override fun onCreate(savedInstanceState: Bundle?, PersistentState: PersistableBundle?) {
        super.onCreate(savedInstanceState, PersistentState)

        GeneratedPluginRegistrant.registerWith(FlutterEngine(this));

    }
    
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
        
        MethodChannel(flutterEngine.dartExecutor, CHANNEL).setMethodCallHandler { call, result ->
            if (call.method == "KML") {
                result.success(getKMLResource());
            } else {
                result.notImplemented();
            }
        }
    }

    private fun getKMLResource(): Int {
        return R.raw.borders;
    }
}

我试图插入下面的调用，但每次都得到一个错误。

override fun onMethodCall(call: MethodCall, result: Result) {
    when (call.method) {
        "showToast" -> {
            val text = call.argument<String>("text") // hello world
            showToast(text)
        }
    }
}

错误：

'onMethodCall' overrides nothing
One type argument expected for class Result<out T>
Unresolved reference: showToast

这是我的flat部分：

Future<void> printSomething(GoogleMapController mapController) async {
    const MethodChannel channel = MethodChannel('flutter.native/helper');
    channel.invokeMethod('showToast', {'text': 'hello world'});
  }

我不知道如何将它正确地合并到我的Kotlin代码中，并且没有太多的例子。至少我找不到。我的最终目标是能够操作私有的fun getKMLResource（）并将return设置为我从flutter应用程序中选择的目录。
有人知道怎么做吗？请帮帮我谢谢你。
下面是我的add kml flutter函数：
下面是我如何选择我的.kml：

Future<void> addKml(GoogleMapController mapController) async {
    const MethodChannel channel = MethodChannel('flutter.native/helper');
    try {
      int kmlResourceId = await channel.invokeMethod('KML');
      return mapController.channel.invokeMethod("map#addKML", <String, dynamic>{
        'resourceId': kmlResourceId,
      });
    } on PlatformException catch (e) {
      throw 'Unable to plot map: ${e.message}';
    }
  }