Flutter platform channel sample code.

android.java

// ...
import io.flutter.app.FlutterActivity;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
import io.flutter.plugin.common.MethodChannel.Result;
// ...

public class MainActivity extends FlutterActivity {

  private static final String PLATFORM_CHANNEL = "elaenor.inometrics.com/platform_channel";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    new MethodChannel(getFlutterView(), PLATFORM_CHANNEL).setMethodCallHandler(
            new MethodCallHandler() {
              @Override
              public void onMethodCall(MethodCall call, Result result) {
                // if (call.method.equals("demoFunction")) { // INFO: method check
                //   String argument = call.argument("data"); // INFO: get arguments
                //   demoFunction(result, argument); // INFO: method call, every method call should pass result parameter
                // } else 
                if (call.method.equals("getNetworks")) {
                  getNetworks(result);
                }
                else if (call.method.equals("connectNetwork")) {
                  String ssid = call.argument("ssid");
                  String password = call.argument("password");
                  connectNetwork(result, ssid, password);
                }
                else {
                  result.notImplemented(); // INFO: not implemented
                }
              }
            }
    );
    GeneratedPluginRegistrant.registerWith(this);
  }
  
  public void demoFunction(Result result, String data) {
    // INFO: function implementation
    if (true) { // INFO: check for some condition
      result.success("android call success with data " + data); // INFO: success response should return through this method
    } else {
      result.error("ERROR", "Error message description!", null); // INFO: error response should return through this method
    }
  }
  
}

flutter.dart

import 'dart:async';

import 'package:flutter/services.dart';

const PLATFORM_CHANNEL = const MethodChannel('<APP_BUNDLE_NAME>/platform_channel');
// you can use whatever you like. but make sure you use the same channel string in native code also

// platform channel method calling
Future<Null> demoFunction(BuildContext context) async {
  try {
    final String result = await PLATFORM_CHANNEL.invokeMethod(
      'demoFunction', // call the native function
      <String, dynamic> { // data to be passed to the function
        'data': 'sample data',
      }
    );
    // result hold the response from plaform calls
  } on PlatformException catch (error) { // handle error
    print('Error: $error'); // here
  }
}

ios.swift

// ... 

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    
    let controller : FlutterViewController = window?.rootViewController as! FlutterViewController;
    let PLATFORM_CHANNEL = FlutterMethodChannel.init(name: "elaenor.inometrics.com/platform_channel", binaryMessenger: controller);
    
    PLATFORM_CHANNEL.setMethodCallHandler({
        (call: FlutterMethodCall, result: FlutterResult) -> Void in
        // if ("demoFunction" == call.method) { // INFO: method check
        //     let arguments = call.arguments as! NSDictionary // INFO: get arguments
        //     demoFunction(result: result, data: arguments["data"] as! String) // INFO: method call, every method call should pass result parameter
        // } else 
        if ("getNetworks" == call.method) {
            getNetworks(result: result) // INFO: method call
        }
        else if ("connectNetwork" == call.method) {
            // Connect to a network with provided SSID & Password
            // This will not work, because we have no permission. So always return an error message.
            result(FlutterError.init(
                code: "NO_PERMISSION",
                message: "Auto connect not possible in iOS devices! Please connect to network manually.",
                details: nil
            ))
        }
        else {
            result(FlutterMethodNotImplemented)
        }
    })
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

func demoFunction(result: FlutterResult, data: String) {
    // INFO: function implementation
    if (true) { // INFO: check for some condition
      result("ios call success with data \(data)") // INFO: success response should return through this method
    } else {
      result(FlutterError.init(
            code: "ERROR",
            message: "Error message description!",
            details: nil
        )) // INFO: error response should return through this method
    }
}

Can you please have an example for ios objective-c. I stuck in one issue as it shows error "Use of undeclared identifier 'controller'".
Here is my code:

• (BOOL)application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary )launchOptions {
  [GeneratedPluginRegistrant registerWithRegistry:self];
  FlutterMethodChannel batteryChannel = [FlutterMethodChannel
  methodChannelWithName:@"foo"
  binaryMessenger: controller];

  [batteryChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
  // TODO
  }];
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
  }

Can you please have an example for ios objective-c. I stuck in one issue as it shows error "Use of undeclared identifier 'controller'".
Here is my code:

The FlutterViewController instance must be created before the FlutterMethodChannel:

FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;

Check the original example

Now, we need to use binaryMesssenger of the controller:

let PLATFORM_CHANNEL = FlutterMethodChannel.init(name: "elaenor.inometrics.com/platform_channel", binaryMessenger: controller.binaryMessenger);

hey @deremakif, thanks for letting me know about this. this gist is an old one. ill update it.