For MQTT.fx I wanted to use ToggleButtons to e.g. choose the de coding of a MQTT Message or the QoS Level:

👁 decode

👁 qos

I found out that in context of a ToggleGroup ToggleButtons behave different than RadioButtons in terms of selection/deselection: unlike RadioButtons ToggleButtons can still be set to unselected state.

A RadioButton extends ToggleButton and overrides fire() (which is invoked when a user gesture indicates that an event for this ButtonBase should occur aka “Button was clicked”):
RadioButton:

@Override public void fire() {
 // we don't toggle from selected to not selected if part of a group
 if (getToggleGroup() == null || !isSelected()) {
 super.fire();
 }
}

ToggleButton:

@Override public void fire() {
 setSelected(!isSelected());
 fireEvent(new ActionEvent());
}

In a ToogleGroup ToggleButtons should behave like RadioButtons, so IMHO this is a bug worth a pull request for ToggleButton ��

One way to handle this is for sure to create a custom extension of ToggleButton implementing fire() in respect to the RadioButton.
But I like more to add behavior to existing controls.
This is my tweak to modify default behavior by adding filters to all ToogleButtons of a ToggleGroup consuming unwanted MouseEvents:

public class JavaFXUtil {

 private static JavaFXUtil me;

 private JavaFXUtil() {
 }

 public static JavaFXUtil get() {
 if (me == null) {
 me = new JavaFXUtil();
 }
 return me;
 }

 public EventHandler<MouseEvent> consumeMouseEventfilter = (MouseEvent mouseEvent) -> {
 if (((Toggle) mouseEvent.getSource()).isSelected()) {
 mouseEvent.consume();
 }
 };

 public void addAlwaysOneSelectedSupport(final ToggleGroup toggleGroup) {
 toggleGroup.getToggles().addListener((Change<? extends Toggle> c) -> {
 while (c.next()) {
 for (final Toggle addedToggle : c.getAddedSubList()) {
 addConsumeMouseEventfilter(addedToggle);
 }
 }
 });
 toggleGroup.getToggles().forEach(t -> {
 addConsumeMouseEventfilter(t);
 });
 }

 private void addConsumeMouseEventfilter(Toggle toggle) {
 ((ToggleButton) toggle).addEventFilter(MouseEvent.MOUSE_PRESSED, consumeMouseEventfilter);
 ((ToggleButton) toggle).addEventFilter(MouseEvent.MOUSE_RELEASED, consumeMouseEventfilter);
 ((ToggleButton) toggle).addEventFilter(MouseEvent.MOUSE_CLICKED, consumeMouseEventfilter);
 }

}

public class ButtonDemoController {
 @FXML
 private ToggleGroup g2;

 @FXML
 private ToggleGroup g3;

 public void initialize() {
 JavaFXUtil.get().addAlwaysOneSelectedSupport(g2);
 JavaFXUtil.get().addAlwaysOneSelectedSupport(g3);
 }

}

👁 buttonofchoice

Example code at GitHub.