Scala: How to create JavaFX keystroke handlers/listeners on a Scene/Stage

By Alvin Alexander. Last updated: May 23, 2020

As a brief note, here are a few examples of how I add some keystroke handlers/listeners to a JavaFX project written in Scala:

// add keystroke listeners/handlers to the scene
def addKeystrokeHandlers(scene: Scene, stage: Stage, theMainPane: MainSplitPane): Unit = {
    configureCommandMHandler(scene, stage)
    // other code was here ...
}

// Minimize (needed to implement manually)
private def configureCommandMHandler(scene: Scene, mainStage: Stage): Unit = {
    val keyComboCommandM: KeyCombination = new KeyCodeCombination(
        KeyCode.M,
        KeyCombination.META_DOWN
    )
    scene.addEventHandler(KeyEvent.KEY_RELEASED, (event: KeyEvent) => {
        if (keyComboCommandM.`match`(event)) {
            mainStage.setIconified(true)
        }
    })
}

The keys for this keystroke-handler solution are knowing how to use the KeyCodeCombination, and how to handle a KeyEvent on the JavaFX Scene. Everything besides that involves implementing your custom logic, such as minimizing the Scene/Stage/Frame in this example. I also use this technique to increase and decrease font size in text editors, like this:

private def decreaseFontSizeHandler(scene: Scene, theMainPane: MainSplitPane): Unit = {
    val decreaseFontSizeKeyCombination: KeyCombination = new KeyCodeCombination(
        KeyCode.MINUS,
        KeyCombination.META_DOWN
    )
    scene.addEventHandler(KeyEvent.KEY_RELEASED, (event: KeyEvent) => {
        if (decreaseFontSizeKeyCombination.`match`(event)) {
            theMainPane.decreaseFontSize()
        }
    })
}

and this:

def decreaseFontSize(): Unit = {
    fontSize -= 1
    editorTextArea.setFont(Font.font("Monaco", FontWeight.NORMAL, fontSize))
    notesTextArea.setFont(Font.font("Monaco", FontWeight.NORMAL, fontSize))
}

Some of that code can be improved, but in summary, if you want to see how to implement JavaFX keystroke handlers/listeners in Scala or Java code, I hope these examples are helpful.

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