Kotlin ClassNotFoundException in a mixed Java and Kotlin Android project

Hi there,
I have an annoying problem. In a mix Android project (Kotlin and Java ) I have made a new Kotlin fragment class but I got ClassNotFoundException only prior to android 5. In the first I thought it was a multidex problem that the Koltin fragment class was not added to the primary dex (The app was exceeding the 64K method). I tried to put this desired fragment class in the primary dex using dexConfig but it did not work as well. I found that app was exceeding the limit a little bit so I removed some dependencies and avoid to use mulidex but unfortunately the problem still happens. When replacing this fragment which is written in Kotlin with a Java one the problem was resolved.
I wish anyone can help me…
Thanks for this great language.
Here is my build.gradle
// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
ext.kotlin_version = ‘1.2.0’
repositories {
jcenter()
// You need to add the following repository to download the
// new plugin.
google()
mavenCentral()
}
dependencies {
classpath ‘com.android.tools.build:gradle:3.0.0’
classpath ‘com.google.gms:google-services:3.1.1’
classpath “org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version”
}
}

allprojects {
    repositories {
        jcenter()
        maven { url 'https://maven.google.com' }
    }
}

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'io.fabric'

repositories {
    maven { url 'http://sdk.uxcam.com/android/' }
    maven { url 'https://maven.fabric.io/public' }
    mavenCentral()
    jcenter()
    maven { url 'https://jitpack.io' }
}

android {
    signingConfigs {
        config {
            keyAlias 'menassah'
            keyPassword 'EAlQDthF0uZeygfjv6pK'
            storePassword '7F-K>[rUiZ'
            storeFile file('./Users/Innovolve')
        }
    }

    lintOptions {
        abortOnError false
        disable 'MissingTranslation'
    }

    packagingOptions {
        exclude 'META-INF/rxjava.properties'
    }

    compileSdkVersion 26
    buildToolsVersion '26.0.3'
    defaultConfig {
        applicationId "com.innovolve.iqraaly"
        minSdkVersion 16
        targetSdkVersion 22
        versionCode 84
        versionName "2.4.1.39"
        multiDexEnabled true
        vectorDrawables.useSupportLibrary = true
    }
    dexOptions {
        javaMaxHeapSize "2g"
    }
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
            signingConfig signingConfigs.config
            debuggable false
            jniDebuggable false
            renderscriptDebuggable false
            shrinkResources true
            buildConfigField 'boolean', 'CRASHLYTICS_ON', 'true'
            buildConfigField 'boolean', 'TESTFAIRY_ON', 'false'
            buildConfigField("String", "BASE_URL", "\"http://mobile.iqraaly.com/api/\"")
        }
        debug {
            debuggable true
            signingConfig signingConfigs.config
            // Disable fabric build ID generation for debug builds
            ext.enableCrashlytics = false
            buildConfigField 'boolean', 'CRASHLYTICS_ON', 'false'
            buildConfigField 'boolean', 'TESTFAIRY_ON', 'true'
            buildConfigField("String", "BASE_URL", "\"http://mobile.iqraaly.com/api/\"")
        }
//      Save TestFairy key
        buildTypes.each {
            it.buildConfigField("String", "TESTFAIRY_KEY", "\"ef8ca53e09a6cccedf5066fcabf3d27b57a4905e\"")
        }
    }
    flavorDimensions "default"
    productFlavors {
        paid {
            applicationId "com.innovolve.iqraaly"
            dimension "default"
        }
        free {
            applicationId "com.innovolve.iqraaly"
            dimension "default"
        }
    }
    sourceSets {
        free {
            res.srcDirs = ['src/free/res']
            java.srcDirs = ['src/free/java']
            main.java.srcDirs += 'src/main/kotlin'
        }
        paid {
            res.srcDirs = ['src/paid/res']
            java.srcDirs = ['src/paid/java']
            main.java.srcDirs += 'src/main/kotlin'
        }
    }
    dataBinding {
        enabled = true
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}
buildscript {
    repositories {
        maven { url 'http://sdk.uxcam.com/android/' }
        jcenter()
        mavenCentral()
        maven { url 'https://maven.fabric.io/public' }
    }
    dependencies {
        classpath 'io.fabric.tools:gradle:1.25.1'
        classpath 'com.google.gms:google-services:3.1.1'
    }
}
dependencies {
    implementation project(':iqraalySDK')
    implementation('com.crashlytics.sdk.android:crashlytics:2.6.8@aar') {
        transitive = true
    }
    implementation files('libs/testfairy-android-sdk-1.5.2.jar')
    // If you want to use the GPU Filters
    implementation 'org.jraf:android-switch-backport:2.0.1'
    implementation 'com.facebook.android:facebook-android-sdk:4.28.0'
    implementation 'com.android.support:support-v4:26.1.0'
    implementation 'com.android.support:customtabs:26.1.0'
    implementation 'com.android.support:cardview-v7:26.1.0'
    implementation 'com.android.support:design:26.1.0'
    implementation 'com.android.support:animated-vector-drawable:26.1.0'
    implementation 'com.android.support:mediarouter-v7:26.1.0'
    implementation 'com.android.support:gridlayout-v7:26.1.0'
    implementation 'com.android.support:multidex:1.0.2'
    implementation 'tk.zielony:carbon:0.15.0.1'
    implementation 'jp.wasabeef:picasso-transformations:2.1.2'
    implementation 'jp.co.cyberagent.android.gpuimage:gpuimage-library:1.4.1'
    implementation 'com.github.vivchar:ViewPagerIndicator:v1.0.1'
    implementation 'com.twotoasters.jazzylistview:library:1.2.1'
    implementation 'com.athkalia.emphasis:emphasis:0.4'
    implementation 'com.google.firebase:firebase-messaging:11.6.2'
    implementation 'com.google.android.gms:play-services:11.6.2'
    implementation 'com.jakewharton.rxbinding2:rxbinding:2.0.0'
    implementation 'com.uxcam:uxcam:2.6.2@aar'
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
}
apply plugin: 'com.google.gms.google-services'
apply plugin: 'kotlin-android-extensions'

Hi Kady,

Did you get the solution for this issue?