Flutter plugin: invoking iOS and Android method including parameters not working

Question

Trying my first Flutter plugin, I try to invoke a method in both, the iOS and the Android-world. I successfully was able to invoke such a method without any parameters.

But now I would like to invoke a method that has parameters.

For iOS, I can't get it to work for some reason. (maybe it is just an autocomplete thing that I keep overseeing since VSCode is not autocompleting my Swift code). But maybe it is something else. Please any help on this.

Here is my code:

My lib (Flutter-world) looks like this:

import 'dart:async';
import 'package:flutter/services.dart';

class SomeName {
  static const MethodChannel _channel =
      const MethodChannel('myTestMethod');

  static Future<String> get sendParamsTest async {
    final String version = await _channel.invokeMethod('sendParams',<String, dynamic>{
        'someInfo1': "test123",
        'someInfo2': "hello",
      });
    return version;
  }
}

.

My swift plugin (iOS-world) looks like this:

import Flutter
import UIKit

public class SwiftSomeNamePlugin: NSObject, FlutterPlugin {

  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "myTestMethod", binaryMessenger: registrar.messenger())
    let instance = SwiftSomeNamePlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {

    // flutter cmds dispatched on iOS device :
    if call.method == "sendParams" {

      guard let args = call.arguments else {
        result("iOS could not recognize flutter arguments in method: (sendParams)") 
      }
      String someInfo1 = args["someInfo1"]
      String someInfo2 = args["someInfo2"]
      print(someInfo1)
      print(someInfo2)
      result("Params received on iOS = \(someInfo1), \(someInfo2)")
    } else {
      result("Flutter method not implemented on iOS")
    }
  }
}

The error messages say:

note: add arguments after the type to construct a value of the type String someInfo1 = args["someInfo1"]

note: add arguments after the type to construct a value of the type String someInfo2 = args["someInfo2"]

note: use '.self' to reference the type object String someInfo1 = args["someInfo1"]

note: use '.self' to reference the type object String someInfo2 = args["someInfo2"]

warning: expression of type 'String.Type' is unused String someInfo1 = args["someInfo1"]

warning: expression of type 'String.Type' is unused String someInfo2 = args["someInfo2"]

MatPag · Accepted Answer · 2020-04-21 10:33:05Z

With the help of miguelpruivo, I found the solution.

Here is the working code:

The Flutter-world in Dart was correct:

import 'dart:async';
import 'package:flutter/services.dart';

class SomeName {
  static const MethodChannel _channel =
      const MethodChannel('myTestMethod');

  static Future<String> get sendParamsTest async {
    final String version = await _channel.invokeMethod('sendParams',<String, dynamic>{
        'someInfo1': "test123",
        'someInfo2': 3.22,
      });
    return version;
  }
}

.

And here below, the iOS-world in Swift - now working as well...

(Dart's dynamic corresponds to Swift's Any)

(the method parameter is a dictionary of type [String:Any] - kind of like Swift's often used userInfo - therefore you need to cast at the receiver handler)...

import Flutter
import UIKit

public class SwiftSomeNamePlugin: NSObject, FlutterPlugin {
  public static func register(with registrar: FlutterPluginRegistrar) {
    let channel = FlutterMethodChannel(name: "myTestMethod", binaryMessenger: registrar.messenger())
    let instance = SwiftSomeNamePlugin()
    registrar.addMethodCallDelegate(instance, channel: channel)
  }

  public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {

    // flutter cmds dispatched on iOS device :
    if call.method == "sendParams" {

      guard let args = call.arguments else {
        return
      }
      if let myArgs = args as? [String: Any],
         let someInfo1 = myArgs["someInfo1"] as? String,
         let someInfo2 = myArgs["someInfo2"] as? Double {
        result("Params received on iOS = \(someInfo1), \(someInfo2)")
      } else {
        result(FlutterError(code: "-1", message: "iOS could not extract " + 
           "flutter arguments in method: (sendParams)", details: nil))
      } 
    } else if call.method == "getPlatformVersion" {
      result("Running on: iOS " + UIDevice.current.systemVersion)
    } else {
      result(FlutterMethodNotImplemented)
    }
  }
}

Miguel Ruivo · Accepted Answer · 2018-12-22 19:49:38Z

1

This looks like a swift syntax error.

You want to do let someInfo1 : String = args[“someInfo1”]

answered Dec 22, 2018 at 19:49

Miguel Ruivo

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1 Comment

iKK Over a year ago

Thank you, miguelpruivo! Of course :). There was too much Dart, Swift, Java mixture these days... ;)... I present the working version as an answer. Again thanks for your hint !!

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