In JavaFX, how do I tell which Stage is in front of another? - javafx

Question

I have a JavaFX application with several Stages open to provide floating windows. I want to iterate through these Stages from front to back. I have a list of all the Stages which I'd like to sort and am looking for a method that will let me compare two of them and determine which is in front. Is there a way to do this?

Answer 1

This is just one possibility.
Store each open Stage in a list that can be observed for changes.
Add a listener on each Stage's focusedProperty. When it changes to true,
Remove the stage from our List and readd it at index 0
Now, create a listener on the List and your "focused" Stage will always be at index 0.
You now have an ArrayList that stores the open stages, in order.
Here is a simple MCVE to demonstrate. There are certainly areas to be improved upon and I welcome suggestions, but this does provide some basic functionality.
OpenStages.java:
import javafx.beans.property.SimpleListProperty;
import javafx.collections.FXCollections;
/**
* Implementation of a SimpleListProperty that will store our ObservableArrayList
*/
public class OpenStages<Stage> extends SimpleListProperty<Stage> {
/**
* Constructor that creates an ObservableArrayList
*/
public OpenStages() {
super(FXCollections.observableArrayList());
}
/**
* Removes this Stage from the list and re-adds it at index 0
*/
public void focusStage(Stage stage) {
this.remove(stage);
this.add(0, stage);
}
}
Main.java:
import javafx.application.Application;
import javafx.collections.ListChangeListener;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) {
// Custom SimpleListProperty that holds our ObservableArrayList of open stages
OpenStages<Stage> openStages = new OpenStages<>();
// Simple interface
VBox root = new VBox(5);
root.setPadding(new Insets(10));
root.setAlignment(Pos.CENTER);
Button btnCreateStage = new Button("Create New Stage");
btnCreateStage.setOnAction(event -> {
// Create a new Stage
Stage newStage = new Stage();
// Add a listener to the focusedProperty of the Stage. When focus changes to true, we
// need to update our openStages list
newStage.focusedProperty().addListener((observable, oldValue, newValue) -> {
if (newValue) {
openStages.focusStage(newStage);
}
});
// Add the stage to our OpenStages list.
openStages.add(newStage);
// Simple layout for the new Stage
VBox stageRoot = new VBox();
stageRoot.setPrefSize(300, 100);
stageRoot.setPadding(new Insets(10));
stageRoot.setAlignment(Pos.CENTER);
// Let's add a label and title to indicate which Stage this is
stageRoot.getChildren().add(new Label("Stage #" + openStages.size()));
newStage.setTitle("Stage #" + openStages.size());
newStage.setScene(new Scene(stageRoot));
// Finally, let's show the stage
newStage.show();
});
// Now, let's create a simple listener for our openStages list to print out the focused Stage
openStages.addListener(new ListChangeListener<Stage>() {
#Override
public void onChanged(Change<? extends Stage> c) {
// Only interested in a stage being added
if (c.next() && c.wasAdded()) {
System.out.println("Focused stage: " + openStages.get(0).getTitle());
}
}
});
// Add the Button to our main layout
root.getChildren().add(btnCreateStage);
// Show the Stage
primaryStage.setScene(new Scene(root));
primaryStage.show();
}
}