flutter FCM notification sound not working in release

Question

I'm struggling last few days with this. I have flutter app that should receive notification from firebase (using FCM) and play custom sound. This works fine if I run app using flutter run or using flutter run --release, but if I build app using flutter build apk --release and install it manually on my phone I still get notification but sound is missing, it won't even play default notification sound.

I checked if my sound is on, and if notification channels in app settings are correct.

main.dart

void main() async {
  // needed if you intend to initialize in the `main` function
  WidgetsFlutterBinding.ensureInitialized();

  fcm.getToken().then((value) {
    print("TOKEN:" + value);
  });

  fcm.configure(
    onResume: (Map<String, dynamic> message) async {},
    onLaunch: (Map<String, dynamic> message) async {},
    onMessage: (Map<String, dynamic> message) async {
       AudioCache _audioCache = AudioCache(
          prefix: "sounds/",
          fixedPlayer: AudioPlayer()..setReleaseMode(ReleaseMode.STOP));

      _audioCache.play('merchant_notify.mp3');
    },
  );

  runApp(MyApp());
}

android/build.gradle

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath 'com.google.gms:google-services:4.3.2'
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
subprojects {
    project.buildDir = "${rootProject.buildDir}/${project.name}"
}
subprojects {
    project.evaluationDependsOn(':app')
   
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

android/app/build.gradle

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
apply plugin: 'com.google.gms.google-services'

android {
    compileSdkVersion 28

    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }

    lintOptions {
        disable 'InvalidPackage'
    }

    defaultConfig {
        applicationId "" 
        minSdkVersion 21
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }

    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig signingConfigs.debug
        }
    }
}

flutter {
    source '../..'
}

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"    
   
}

androidmanifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
    package="">

    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.VIBRATE"/>
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
    <application
        android:name="io.flutter.app.FlutterApplication"
        android:label=""
        android:icon="@mipmap/launcher_icon">
        <activity
           android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize"
            android:showWhenLocked="true"
            android:turnScreenOn="true">

            <meta-data
              android:name="io.flutter.embedding.android.NormalTheme"
              android:resource="@style/NormalTheme"
              />

            <meta-data
              android:name="io.flutter.embedding.android.SplashScreenDrawable"
              android:resource="@drawable/launch_background"
              />
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>

            <intent-filter>
                <action android:name="FLUTTER_NOTIFICATION_CLICK"/>
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter> 
        </activity>
       
        <receiver android:name="com.dexterous.flutterlocalnotifications.ScheduledNotificationBootReceiver">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED"/>
                <action android:name="android.intent.action.MY_PACKAGE_REPLACED"/>
                <action android:name="android.intent.action.QUICKBOOT_POWERON" />
                <action android:name="com.htc.intent.action.QUICKBOOT_POWERON"/>
            </intent-filter>
        </receiver>

       
        <!-- Don't delete the meta-data below.
             This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
       <meta-data
            android:name="flutterEmbedding"
            android:value="2" /> 
    </application>
</manifest>

MainActivity.kt

package com.example.merchant_delivery

import io.flutter.embedding.android.FlutterActivity



class MainActivity: FlutterActivity()  { 
}

Also there is sound file in res\raw\sound.mp3

Here is json that I send to firebase FCM:

{
    "registration_ids": [
       
    ],
      "notification": {
        "title": "Test notification",
        "body": "Body test",
        "android_channel_id": "channel_name",
        "channel_id": "channel_name",
        "sound": "sound",
        "priority":"high"
    }
}

Answer 1

<resources xmlns:tools="http://schemas.android.com/tools" tools:keep="@raw/{filename}"/>

add this in the keep.xml which is inside the raw folder of the android resource directory. while creating the release build it actually shrinks the file and changes the name so this is what i got for the solutions.

Answer 2

try this in your MainActivity.java

    import io.flutter.embedding.android.FlutterActivity;   
    import android.app.NotificationChannel;  
    import android.app.NotificationManager;  
    import android.media.AudioAttributes;  
    import android.net.Uri;  
    import android.os.Build;   
    import android.os.Bundle;   
    public class MainActivity extends FlutterActivity {  
@Override  
 protected void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);   
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {  
  Uri soundUri=Uri.parse("android.resource://"+getApplicationContext()   
.getPackageName() + "/" +  R.raw.[soundName without extension]);  
AudioAttributes audioAttributes = new AudioAttributes.Builder()   
                .setContentType(AudioAttributes.CONTENT_TYPE_SONIFICATION)    
                .setUsage(AudioAttributes.USAGE_ALARM)   
                .build();   

        // Creating Channel   
        NotificationChannel channel = new NotificationChannel([ChannelId],[ChannelName], NotificationManager.IMPORTANCE_HIGH);
        channel.setSound(soundUri, audioAttributes);

        NotificationManager notificationManager = getSystemService(NotificationManager.class);
        notificationManager.createNotificationChannel(channel);
    }
   // GeneratedPluginRegistrant.registerWith(this);
}

}