Prevent an accordion in JavaFX from collapsing - accordion

Question

Is there an easy way of preventing an accordion in JavaFX 2.1 from fully collapsing? I have an accordion with a few entries but if the user clicks the active accordion entry it collapses the accordion.
I could probably use a mouse click listener to check do the check and act accordingly but this feels like it should be even simpler than that to accomplish.

Answer 1

Add a listener to the currently expanded accordion pane and prevent it from being collapsed by the user by modifying it's collapsible property.
Here is a sample app:
import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.value.*;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.stage.Stage;
public class AccordionSample extends Application {
public static void main(String[] args) { launch(args); }
#Override public void start(Stage primaryStage) {
// create some titled panes to go in an accordion.
TitledPane adminPane = new TitledPane("Animals",
VBoxBuilder.create().style("-fx-padding: 10").spacing(10).children(
ButtonBuilder.create().text("Zebra").maxWidth(Double.MAX_VALUE).build(),
ButtonBuilder.create().text("Shrew").maxWidth(Double.MAX_VALUE).build()
).build()
);
TitledPane viewPane = new TitledPane("Vegetables",
VBoxBuilder.create().style("-fx-padding: 10").spacing(10).children(
ButtonBuilder.create().text("Eggplant").maxWidth(Double.MAX_VALUE).build(),
ButtonBuilder.create().text("Carrot").maxWidth(Double.MAX_VALUE).build()
).build()
);
// create an accordion, ensuring the currently expanded pane can not be clicked on to collapse.
Accordion accordion = new Accordion();
accordion.getPanes().addAll(adminPane, viewPane);
accordion.expandedPaneProperty().addListener(new ChangeListener<TitledPane>() {
#Override public void changed(ObservableValue<? extends TitledPane> property, final TitledPane oldPane, final TitledPane newPane) {
if (oldPane != null) oldPane.setCollapsible(true);
if (newPane != null) Platform.runLater(new Runnable() { #Override public void run() {
newPane.setCollapsible(false);
}});
}
});
for (TitledPane pane: accordion.getPanes()) pane.setAnimated(false);
accordion.setExpandedPane(accordion.getPanes().get(0));
// layout the scene.
StackPane layout = new StackPane();
layout.setStyle("-fx-padding: 10; -fx-background-color: cornsilk;");
layout.getChildren().add(accordion);
primaryStage.setScene(new Scene(layout));
primaryStage.show();
}
}

Answer 2

Here is another solution for making sure the accordion will never completely collapse. The difference from the great original answer by #jewelsea is little - I didn't like the fact that the default down facing arrow was disappearing from the open accordion TitledPane face, because its "collapsible" property is being set to false. I played with it a bit more to achieve a more "natural" feel for my interface.
/* Make sure the accordion can never be completely collapsed */
accordeon.expandedPaneProperty().addListener((ObservableValue<? extends TitledPane> observable, TitledPane oldPane, TitledPane newPane) -> {
Boolean expand = true; // This value will change to false if there's (at least) one pane that is in "expanded" state, so we don't have to expand anything manually
for(TitledPane pane: accordeon.getPanes()) {
if(pane.isExpanded()) {
expand = false;
}
}
/* Here we already know whether we need to expand the old pane again */
if((expand == true) && (oldPane != null)) {
Platform.runLater(() -> {
accordeon.setExpandedPane(oldPane);
});
}
});