sarahgerweck / scalafx-utils   0.14.3


ScalaFX Utilities

Scala versions: 2.12 2.11

Sarah’s ScalaFX Utilities

This project contains helper functions, utilities and convenience functions for working with JavaFX and ScalaFX in Scala.

ScalaFX does a tremendous job at making JavaFX more usable from Scala, but it doesn't go as far as it could in facilitating functional and reactive programming. This project is an attempt to add additional facilities that further bridge the beautiful paradigms of Scala with the powerful UI functionality offered JavaFX.

In particular, here are some key features:

  • Monadic and applicative interfaces on top of Observable make it easy to build up computations.
  • Converters that allow you to use a Future or Akka Stream as an Observable.

This code is offered as is with no guarantees. You are free to use it if you find it useful, but this is not part of any production project and it may have serious bugs. These APIs may also change at any time, and I make no guarantees that the project will be maintained at all. I welcome any bug reports and I will be happy to merge high-quality pull requests if you find a bug.


To use ScalaFX, add the following to your SBT build:

libraryDependencies += "org.gerweck.scala" %% "scalafx-utils" % "0.14.3"

This currently supports both Scala 2.11 and 2.12. Scala 2.11 will remain a first-class citizen until Scala 2.13 is released unless it would require substantial forking.


The primary use of this library is to provide a number of implicit conversions and instances, which are all brought into scope with this import:

import org.gerweck.scalafx.util._

If you use Cats, this makes ScalaFX observables instances of Functor, Applicative and Monad. It also provides some simple extension methods along these lines.

Functional Transformations

Note that the output of a functional transformation is always a ReadOnlyObjectProperty[A], even if there exists a more specific result type like ReadOnlyIntegerProperty that would work. (The types used by ScalaFX are fairly complicated, and no real harm is done by using an ObjectProperty in all cases.)


To facilitate functional programming, the standard map function allows you to transform an observable value using a pure function.

Note that, for performance reasons, these functionally defined observables do not trigger an update if an input or output value is changed to one that is identical as defined by equals.

import scalafx.beans.value._
import scalafx.scene.control._
import org.gerweck.scalafx.util._

val textBox = new TextField { /* ... */ }
val boxText: ObservableValue[String, String] = textBox.text
/* Construct a new observable derived from the underlying one using `map` */
val characterCount: ReadOnlyObjectProperty[String] = textBox.text map (_.size)

Multiple Function Inputs

If your function depends on several observable values, you can use the applicative behavior provided by the library. The Cats applicative functionality is all available, but there is a more convenient mechanism for the most common use case where you want to operate on a tuple.

import org.gerweck.scalafx.util._

val startedDownloads = IntegerProperty(0)
val finishedDownloads = IntegerProperty(0)
val runningDownloads: ReadOnlyObjectProperty[Int] =
  (startedDownloads, finishedDownloads).observe map {
    case (st, fi) => st - fi

This observe extension method is available on tuples of any arity and efficiently processes updates from any of its dependent values.

Monadically Chained Observables

In addition to the behavior of an applicative functor, this library also provides the ability to act like a monadic functor by providing flatMap and flatten. Where possible use the applicative syntax defined above rather than a chain of flatMap applications: the applicative format performs much better.

Here is an example of a model where you might have a dialog box or window. In this window, you could have a list selection where you choose from one of many transformation types. Once you've selected a transformation type, it will display a configuration panel that you can use to control the details of that transformation.

import org.gerweck.scalafx.util._

/** An object that has a config dialog that produces a function */
trait ConfigurableIntFunction {
  val typeName: String
  val configPanel: scalafx.scene.layout.Pane
  val currentFunction: ReadOnlyObjectProperty[Int => Int]
val selectedFunctionType: ObjectProperty[ConfigurableIntFunction] = ???
val selectedFunction = selectedFunctionType flatMap (_.currentFunction)
val inputInt = IntegerProperty(0)
val outputInt =
  (selectedFunction, inputInt).observe map {
    case (sf, ii) => sf(ii)