Tower Tower - 3 months ago 30
Scala Question

Getting started on Scala + JavaFX desktop application development

Is there some guide or walkthrough to building a Scala + JavaFX desktop application?

I'm having hard time finding a good source and I am using IntelliJ IDEA as the IDE.

Even the most simplistic desktop hello world samples would help a lot, because I have little clue where to start.

Update: This is what I have now:

import javafx.application.Application
import javafx.scene.Scene
import javafx.scene.layout.StackPane
import javafx.stage.Stage
import javafx.scene.control.Label

class Test extends Application {
override def start(primaryStage: Stage) {
primaryStage.setTitle("Sup!")

val root = new StackPane
root.getChildren.add(new Label("Hello world!"))

primaryStage.setScene(new Scene(root, 300, 300))
primaryStage.show()
}
}

object Test {
def main(args: Array[String]) {
val t = new Test
t.start(new Stage)
}
}


Running it I get:


Exception in thread "main" java.lang.IllegalStateException: Not on FX
application thread; currentThread = main


How can I get it to display the hello world window with the label?

Answer

There are a few things to know when writing Scala based JavaFX applications.

First, here's a sample hello world app:

import javafx.application.Application
import javafx.scene.Scene
import javafx.scene.layout.StackPane
import javafx.stage.Stage
import javafx.scene.control.Label

class Test extends Application {
  println("Test()")

  override def start(primaryStage: Stage) {
    primaryStage.setTitle("Sup!")

    val root = new StackPane
    root.getChildren.add(new Label("Hello world!"))

    primaryStage.setScene(new Scene(root, 300, 300))
    primaryStage.show()
  }
}

object Test {
  def main(args: Array[String]) {
    Application.launch(classOf[Test], args: _*)
  }
}

Running it you should get:

enter image description here

Here's an official hello world example in Java: http://docs.oracle.com/javafx/2/get_started/hello_world.htm

The main differences are:

  • You have to write the so-called companion object with the def main() that launches the actual application.
  • You have to specify that it will be run in context of the class Test, and not the companion object: Application.launch(classOf[Test], args: _*).

If you just try to run the application directly with Application.launch(args : _*) you will get this error:

Exception in thread "main" java.lang.RuntimeException: Error: class Test$ is not a subclass of javafx.application.Application

To learn more about JavaFX, just read the official documentation: http://docs.oracle.com/javafx/index.html