randomly displaying circles within gridPane cells

Question

I am creating am application that displays circles (of different colors) randomly within each cell of a gridPane.

What i want to do is create a "shuffle" button that changes the position of each circle randomly within the gridPane. However, I keep running into a slurry of problems.

Here is what i have so far. My two classes (have not added XML file):

Controller Class

public class viewController {

//My two Variables, a gridPane and a button

    @FXML
    private GridPane matrix;
    @FXML
    private Button shuffleBut;


//my eventHandler event that should (1) add circles to all the cells, and 
(2) shuffle them amongst the cells in the gridPane.  

void shuffle(ActionEvent e) {
    Random r = new Random ();
    int rowShuffle = r.next((4-0)+1);
    int colShuffle = r.next((4-0)+1);
    Circle newCircle = new Circle ();
    matrix.add(newCircle, rowShuffle,  colShuffle );

}

Main Class

public class Main extends Application {

@Override
public void start(Stage primaryStage) throws Exception {

    // just load fxml file and display it in the stage:


    Parent root = FXMLLoader.Load(getClass().getResource("mainUI.fxml"));
    Scene scene = new Scene(root);
    primaryStage.setScene(scene);
    primaryStage.show();
}

// main method to support non-JavaFX-aware environments:

public static void main(String[] args) {
    // starts the FX toolkit, instantiates this class, 
    // and calls start(...) on the FX Application thread:
    launch(args); 
}

Answer 1

Here is an example that demos how to shuffle Circles around in a GridPane. If you add the Circles to an ArrayList, you can remove the Circles from the GridPane. Then you can shuffle the List. Finally, you can add the shuffled list back to the GridPane.

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Control;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

/**
 *
 * @author blj0011
 */
public class JavaFXApplication314 extends Application
{

    Random random = new Random();
    int numberOfRows = 25;
    int numberOfColumns = 25;

    @Override
    public void start(Stage primaryStage)
    {
        List<Circle> circles = new ArrayList();
        for (int i = 0; i < numberOfColumns * numberOfRows; i++) {
            circles.add(new Circle(10, getRandomColor()));
        }

        GridPane gridPane = new GridPane();
        addCirclesToGridPane(gridPane, circles);
        gridPane.setPadding(new Insets(20, 20, 20, 20));

        Button btn = new Button();
        btn.setText("Say 'Hello World'");
        btn.setOnAction((ActionEvent event) -> {
            Collections.shuffle(circles);//Shuffle the List of Circles.
            for(int i = 0; i < numberOfColumns * numberOfRows; i++) 
            { 
                Circle c = circles.get(i); 
                GridPane.setColumnIndex(c, i % numberOfColumns); 
                GridPane.setRowIndex(c, i / numberOfColumns); 
            }
        });

        VBox vBox = new VBox(gridPane, new StackPane(btn));
        vBox.setMaxSize(Control.USE_COMPUTED_SIZE, Control.USE_COMPUTED_SIZE);
        StackPane root = new StackPane(vBox);
        root.setMaxSize(Double.MAX_VALUE, Double.MAX_VALUE);
        Scene scene = new Scene(root);

        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args)
    {
        launch(args);
    }

    public void addCirclesToGridPane(GridPane gridPane, List<Circle> circles)
    {
        for (int i = 0; i < numberOfColumns * numberOfRows; i++) {
            gridPane.add(circles.get(i), i % numberOfColumns, i / numberOfColumns);
        }
    }

    public Color getRandomColor()
    {
        int r = random.nextInt(255);
        int g = random.nextInt(255);
        int b = random.nextInt(255);

        return Color.rgb(r, g, b);
    }
}