如何从 swift 本机代码（AppDelegate）调用（Invoke）dart 方法？“invokeMethod”在 android 上工作，但在 ios 上不起作用

Question

我正在尝试使用flutter通道的invokeMethod从ios的AppDelegate类调用dart文件（main.dart）中的函数（“onRazorPayPaymentFail”方法）。但它不起作用。onRazorPayPaymentFail方法在Android上触发。但在iOS中它不管用。

//lib 文件夹中的 main.dart

//main.dart from lib folder
class _MyHomePageState extends State<MyHomePage> {
  static const razorpay_platform =
      const MethodChannel('com.algorin.pf.razorpay');

  @override
  void initState() {
    super.initState();
    razorpay_platform.setMethodCallHandler(myUtilsHandler);
  }

  Future<dynamic> myUtilsHandler(MethodCall methodCall) async {
    switch (methodCall.method) {
      case 'onRazorPayPaymentFail':
        print(json.decode(methodCall.arguments));
        break;
      case 'onRazorPayPaymentSuccess':
        processSuccessResponse(json.decode(methodCall.arguments));
        break;
      default:
    }
  }
//..................................
}}

和 AppDelegate.Swift 文件

//AppDelegate.Swift  file
import UIKit 
import Flutter 
import Razorpay 
@UIApplicationMain 
@objc class AppDelegate : FlutterAppDelegate,
RazorpayPaymentCompletionProtocol {
    //..............
    var controller : FlutterViewController!;
    var RAZORPAY_IO_CHANNEL : FlutterMethodChannel!;

    override func application (
        _ application : UIApplication,
        didFinishLaunchingWithOptions launchOptions : [UIApplicationLaunchOptionsKey: Any]?)->
Bool {
    controller = window?.rootViewController as? FlutterViewController;
    RAZORPAY_IO_CHANNEL = FlutterMethodChannel (
        name : "com.algorin.pf.razorpay",
        binaryMessenger : controller
    )
    GeneratedPluginRegistrant.register (with: self);
    return super.application (
        application,
        didFinishLaunchingWithOptions : launchOptions
    );
}

public func onPaymentError (_ code: Int32, description str: String)
{
    print (
        "<<<<<<<<<<< Payment Failed >>>>>>>>>>>>>>>>>>>>>>>>>>>"
    );
    RAZORPAY_IO_CHANNEL.invokeMethod ("onRazorPayPaymentFail", arguments: str);
}
//............
}