Event handlers

Event handlers are implementations of the javafx.event.EventHandler interface, and can be set on event handler properties with an fx:Evaluate or fx:Observe expression:

com/sample/MyControl.fxml

<StackPane xmlns="http://javafx.com/javafx" xmlns:fx="http://jfxcore.org/fxml/2.0"
           fx:subclass="com.sample.MyControl">
    <Button onAction="$myActionHandler"/>
</StackPane>

com/sample/MyControl.java

public class MyControl extends MyControlBase {
    final EventHandler<ActionEvent> myActionHandler = (event) -> {
        ...
    };

    public MyControl() {
        initializeComponent();
    }
}

Usually, event handlers don’t change dynamically. It is therefore advisable to use fx:Evaluate instead of fx:Observe.

Method event handlers

Event handlers can also be implemented as methods on the code-behind class that have a signature compatible with the javafx.event.EventHandler interface. The method name must be prefixed with # in the FXML attribute:

com/sample/MyControl.fxml

<StackPane xmlns="http://javafx.com/javafx" xmlns:fx="http://jfxcore.org/fxml/2.0"
           fx:subclass="com.sample.MyControl">
    <!-- Note that # identifies a method handler -->
    <Button onAction="#handleActionEvent"/>
</StackPane>

com/sample/MyControl.java

public class MyControl extends MyControlBase {
    public MyControl() {
        initializeComponent();
    }
    
    void handleActionEvent(ActionEvent event) {
        ...
    }
}

The event parameter is optional in the method signature and can be omitted if not required.