This guide describes how to write custom platform-specific code.

As I read this article, I thought it would be confusing for a beginner.

In this post I took a simpler approach, for example opening the settings screen on Android and iOS from your app.

Overview

Scope: Android(Kotlin) and iOS(Swift 5)
Feature: open setting screen form your app.

iOS

Open Settings screen

Android

Open Settings screen

Flutter Channel

Create channel

All channel names used in a single app must be unique; prefix the channel name with a unique ‘domain prefix’, for example:

Define App Id

This is application Id(Android) or bundle Id (iOS)

static const String appID = "com.example";

Define Feature Name

featureName= "settings";

Define Channel

final String channelName= "$appID/$featureName";

static const MethodChannel platform = MethodChannel(channelName);

Invoke a method on the method channel

Create method name

Define method name

static const String methodOpenAppSettingScreen = "openAppSettingScreen";

Define method invoke

invoke a method on the method channel, specifying the concrete method to call using the String identifier openAppSettingScreen.

The call might fail—for example if the platform does not support the platform API (such as when running in a simulator)—so wrap the invokeMethod call in a try-catch statement.

Future<bool> openAppSettingScreen({final Function? onError}) async {
    try {
      final bool result =
          await platform.invokeMethod(methodOpenAppSettingScreen);
      return result;
    } on PlatformException catch (e) {
      if (kDebugMode) {
        print(e.toString());
      }
      return false;
    }
  }

The method await platform.invokeMethod(methodOpenAppSettingScreen) return data type bool.

When you calling platform-specific iOS and Android code using platform channels, you must return same data type.

Check the table shows how Dart values are received on the platform side and vice versa:

Flutter(Dart): bool
Android(Kotlin) : Boolean
iOS(Swift): Bool

Add an Android(Kotlin) platform-specific implementation

Create configure Flutter Engine

open file MainActivity.kt
create method configureFlutterEngine

Screen Shot 2022-04-19 at 21 23 23

class MainActivity: FlutterActivity() {

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
    }
}

Add channel name and method name

The channel name and method name are must be same value as Flutter channel

    companion object {
        private const val APP_ID: String = "com.example"
        private const val FEATURE_NAME: String = "settings"
        private const val CHANNEL_NAME: String = "$APP_ID/$FEATURE_NAME"
        private const val METHOD_OPEN_APP_SETTING_SCREEN: String = "openAppSettingScreen"
    }

Implement open setting screen

    fun openSettingScreen(): Boolean {
        val intentSetting = Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS).apply {
            data = Uri.fromParts("package", packageName, null)
        }
        return try {
            startActivity(intentSetting)
            true
        } catch (e: Exception) {
            false
        }
    }

Remember method openSettingScreen will return Boolean type.

Detect channel name on method configureFlutterEngine

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL_NAME).setMethodCallHandler {
                call, result ->
            if (call.method == METHOD_OPEN_APP_SETTING_SCREEN) {
                // TODO
                return@setMethodCallHandler
            }
        }
    }

Implement method and handle result

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL_NAME).setMethodCallHandler {
                call, result ->
            if (call.method == METHOD_OPEN_APP_SETTING_SCREEN) {
                result.success(openSettingScreen())
                return@setMethodCallHandler
            }
        }
    }

Add an iOS platform-specific implementation

Create configure Flutter Engine

open file AppDelegate.swift on Xcode

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }

define controller

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
    
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

Add channel name and method name

The channel name and method name are must be same value as Flutter channel

    let appID = "com.example"
    let featureName = "settings"
    let methodOpenAppSettingScreen = "openAppSettingScreen"
    
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
        let channelName = "\(self.appID)/\(self.featureName)"
        
        
        GeneratedPluginRegistrant.register(with: self)
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }

Implement open setting screen

    
    private func openSettingScreen() -> Bool {
        if let url = URL(string:UIApplication.openSettingsURLString) {
            if UIApplication.shared.canOpenURL(url) {
                if #available(iOS 10.0, *) {
                    do {
                        try  UIApplication.shared.open(url, options: [:], completionHandler: nil)
                        return true
                    } catch {
                        return false
                    }
                    
                }
                return UIApplication.shared.openURL(url)
                
            }
        }
        
        return false
    }

Remember method openSettingScreen will return Bool type.

Find Flutter channel on method application and detect method name

    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
        let channelName = "\(self.appID)/\(self.featureName)"
        
        let settingChannel = FlutterMethodChannel(name: channelName,
                                                  binaryMessenger: controller.binaryMessenger)
        settingChannel.setMethodCallHandler({
            (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
            if (call.method == self.methodOpenAppSettingScreen) {
                // TODO
            }
            
        })
        
        GeneratedPluginRegistrant.register(with: self)
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }

Implement method and handle result

    
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
        let channelName = "\(self.appID)/\(self.featureName)"
        
        let settingChannel = FlutterMethodChannel(name: channelName,
                                                  binaryMessenger: controller.binaryMessenger)
        settingChannel.setMethodCallHandler({
            (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
            if (call.method == self.methodOpenAppSettingScreen) {
                result(self.openSettingScreen())
            }
            
        })
        
        GeneratedPluginRegistrant.register(with: self)
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }
    

Apply Channel Method

Future<void> _onSetting() async {
    final SettingChannel settingChannel = SettingChannel();
    await settingChannel.openAppSettingScreen();
}

Source code

https://github.com/ttpho/flutter-setting-app/blob/main/settings/lib/main.dart

Note

Cover Photo

Thumbnail Photo

Platform-specific code