java.lang.ClassNotFoundException: Didn't find class "com.my.app.example.Main" on path: DexPathList

Question

I'm having a hard time exactly what is causing this error on adb because I am using Kotlin, TornadoFX (a JavaFX Kotlin library) and Gluon with JFXMobile. When I use Gluon's androidInstall to build my project I encounter this error, along with a black screen:

java.lang.ClassNotFoundException: Didn't find class "com.my.app.example.Main" on path: DexPathList

I'm trying to use JavaFX 3D in this application, but I don't think that it's causing the error.

I checked my Android Manifest, and the package name is the same as my project.

My project hierarchy is like so:

root
  libs
  src
    android
    ios
    main
      kotlin
        com.my.app.example
          Main.kt

Which might be causing Android to not be able to find the file? Since there's no Java folder.

I have all of the following in my gradle file, compiled successfully:

apply plugin: 'kotlin'
apply plugin: 'idea'
apply plugin: 'java'
apply plugin: 'javafx-gradle-plugin'
apply plugin: 'org.javafxports.jfxmobile'
apply plugin: 'org.jetbrains.kotlin.android.extensions'

dependencies {
  compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
  compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
  compile 'no.tornado:tornadofx:1.7.12'
  compile 'no.tornado:tornadofx-android-compat:1.0.1'
  compile 'com.gluonhq:charm:4.3.7'
  compile fileTree(dir: 'libs', include: '*.jar')
}

The fileTree(dir: 'libs', include: '*.jar') is for an external library that I am using to import ObjModels for JavaFX, located in the libs folder of my project.

Things I am suspicious of causing this error:

1. Me not having the right things in my Gradle file because I am terrible with Gradle.
2. The .jar in my libs folder not being included correctly in the Android apk and messing it all up somehow
3. Kotlin file hierarchy somehow making Android not able to find the Main class, or the fact that it's Main.kt instead of Main.java

Please note that this project runs fine on my desktop, so it's not a problem with my source code, just something on the Android-specific end.

Any ideas what is causing this? Thanks for any help!

Answer 1

This is a very simple sample of a Gluon Mobile project working with Kotlin that can be deployed to Android/iOS.

Using the Gluon plugin for IntelliJ, created a project (Single View), and modify the build.gradle file:

build.gradle

buildscript {
    ext.kotlin_version = '1.1.51'
    repositories {
        mavenCentral()
        jcenter()
    }

    dependencies {
        classpath 'org.javafxports:jfxmobile-plugin:1.3.9'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

apply plugin: 'kotlin'
apply plugin: 'idea'
apply plugin: 'java'
apply plugin: 'org.javafxports.jfxmobile'
apply plugin: 'org.jetbrains.kotlin.android.extensions'

repositories {
    jcenter()
    mavenCentral()
    maven {
        url 'http://nexus.gluonhq.com/nexus/content/repositories/releases'
    }
}

mainClassName = 'com.gluon.kotlin.Main'

dependencies {
    compile 'com.gluonhq:charm:4.4.1'
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
    compile "org.jetbrains.kotlin:kotlin-reflect:$kotlin_version"
    compile 'no.tornado:tornadofx:1.7.12'
    compile 'no.tornado:tornadofx-android-compat:1.0.1'

}
jfxmobile {
    downConfig {
        version = '3.6.0'
        plugins 'display', 'lifecycle', 'statusbar', 'storage'
    }
    android {
        manifest = 'src/android/AndroidManifest.xml'
    }
    ios {
        infoPList = file('src/ios/Default-Info.plist')
        forceLinkClasses = [
                'com.gluonhq.**.*',
                'javax.annotations.**.*',
                'javax.inject.**.*',
                'javax.json.**.*',
                'org.glassfish.json.**.*'
        ]
    }
}

Remove the /src/main/java package, and add the /src/main/kotlin one.

The Main.kt class is in /src/main/kotlin/com/gluon/kotlin/Main.kt:

Main.kt

package com.gluon.kotlin

import com.gluonhq.charm.glisten.application.MobileApplication
import com.gluonhq.charm.glisten.mvc.View
import com.gluonhq.charm.glisten.visual.MaterialDesignIcon
import javafx.geometry.Pos
import javafx.scene.control.Button
import javafx.scene.control.Label
import javafx.scene.layout.VBox
import tornadofx.plusAssign

class Main: MobileApplication() {

    override fun init() {
        addViewFactory(MobileApplication.HOME_VIEW, {
            val view = View("home")

            val vBox = VBox()
            with (vBox) {
                alignment = Pos.CENTER
                spacing = 30.0
                this += Button("Kotlin", MaterialDesignIcon.CODE.graphic()).apply {
                    println("Click")
                }
                this += Label("Gluon Mobile - Kotlin")
            }
            with(view) {
                this.center = vBox
                this.setOnShown {
                    with(MobileApplication.getInstance().appBar) {
                        this.navIcon = MaterialDesignIcon.MENU.button().apply {
                            println("Click")
                        }
                        this.titleText = "Gluon Mobile - Kotlin"
                    }
                }
            }
            view
        })
    }

}

You can run the project on desktop, and without modifying the AndroidManifest file, deploy to an Android device using the androidInstall task.