Hey there! Let's tackle this problem step by step since you're working with Flutter and don't have much Kotlin experience. Controlling app icon badge counts when your app is terminated and receives a notification is platform-specific, so we'll break down Android and iOS separately.

Android Implementation #

Android doesn't have a system-wide standard for app badges—each manufacturer (Xiaomi, Huawei, Samsung, etc.) uses its own API. That means we need to handle these differences, either with a Flutter plugin or simplified Kotlin code (don't worry, I'll keep the Kotlin part straightforward).

Option 1: Use a Flutter Plugin (Easier for Kotlin Newbies) #

The flutter_app_badger plugin wraps native badge logic for most major Android brands. Here's how to set it up:

1. Add the dependency to your pubspec.yaml:

   dependencies:
     flutter_app_badger: ^1.5.0
   

2. Important: When your app is terminated, Flutter's Dart code won't run. So you still need a tiny bit of Kotlin to handle badge updates when notifications arrive. Here's a simplified FirebaseMessagingService implementation (assuming you're using Firebase Cloud Messaging):

   import com.google.firebase.messaging.FirebaseMessagingService
   import com.google.firebase.messaging.RemoteMessage
   import io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingService
   import me.leolin.shortcutbadger.ShortcutBadger // Add this library for broader support
   
   class MyFirebaseMessagingService : FlutterFirebaseMessagingService() {
       override fun onMessageReceived(remoteMessage: RemoteMessage) {
           super.onMessageReceived(remoteMessage)
           
           // Pull the badge count from your notification data (or hardcode for testing)
           val badgeCount = remoteMessage.data["badge"]?.toInt() ?: 1
           
           // Update the badge using ShortcutBadger (supports most Android brands)
           ShortcutBadger.applyCount(this, badgeCount)
       }
   }
   

3. Add the ShortcutBadger dependency to your Android build.gradle (Module level):

   dependencies {
       implementation 'me.leolin:ShortcutBadger:1.1.22@aar'
   }
   

4. Register the service in your AndroidManifest.xml:

   <service
       android:name=".MyFirebaseMessagingService"
       android:exported="false">
       <intent-filter>
           <action android:name="com.google.firebase.MESSAGING_EVENT" />
       </intent-filter>
   </service>
   

Option 2: Manual Manufacturer-Specific Code (If You Avoid Plugins) #

If you don't want to use a plugin, you can write code for individual brands, but this is more maintenance-heavy. For example, here's how to handle Xiaomi devices:

try {
    val miuiNotificationClass = Class.forName("android.app.MiuiNotification")
    val field = miuiNotificationClass.getField("extraNotification")
    val extraNotification = field.get(null)
    val method = extraNotification.javaClass.getMethod("setBadgeCount", Int::class.java)
    method.invoke(extraNotification, badgeCount)
} catch (e: Exception) {
    // Fallback for other brands or errors
}

iOS Implementation #

iOS has built-in support for app badges, so this is much simpler:

1. When sending notifications via APNs (or Firebase Cloud Messaging), include the badge field in your payload. For example:

   {
     "aps": {
       "alert": "Your new notification",
       "badge": 2,
       "sound": "default"
     }
   }
   

   The iOS system will automatically update the app icon badge when the notification arrives—even if your app is terminated.
2. When the user opens your app, don't forget to reset the badge count. You can do this with the flutter_app_badger plugin in Dart:

   import 'package:flutter_app_badger/flutter_app_badger.dart';
   
   void resetBadge() async {
     await FlutterAppBadger.removeBadge();
   }
   

Key Takeaways #

• Android: Since there's no universal API, rely on libraries like ShortcutBadger to cover most manufacturers. You need native Kotlin code to handle badge updates when the app is terminated (Dart code won't run then).
• iOS: Let the system handle it by including the badge field in your notification payload. Just remember to reset the badge when the app opens.
• Flutter Plugins: flutter_app_badger simplifies cross-platform badge management, but Android still needs that small native code snippet for terminated state handling.

内容的提问来源于stack exchange，提问作者Get Malone