How to add a MouseListener to each individual element in a GridLayout?

Question

I have some code that creates a grid of coloured buttons that I would like to attach mouse listeners to. Ideally, I'd want the program to print a line (e.g. "button entered!") every time my mouse enters any one of these buttons.

However, my current code only prints this message out when the grid itself is entered.

My code is here:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.net.URL;

public class ColorGrid implements MouseListener {

/*
    Frame holds the panel
    Panel holds the grid framework and the toolbar
*/
JFrame frame = new JFrame();
JLabel[][] grid;
JToolBar toolbar = new JToolBar("Test");
ButtonGroup bgroup = new ButtonGroup();
JPanel panel = new JPanel();

// Example strings for default button implementations - not needed
static final private String PREVIOUS = "previous";
static final private String UP = "up";
static final private String NEXT = "next";

// holds strings that point to URL of button elements
String[] buttonPics = {"images/circle_blue.png", "images/circle_green.png", "images/circle_orange.png", "images/circle_red.png", "images/circle_yellow.png"};
Random rand = new Random();

/*
    CONSTRUCTOR

    Add buttons to the toolbar
    Set layouts for the frame and panel
    Populate grid with icons (representing buttons)

*/
public ColorGrid(int width, int length) {

    addButtons(bgroup, toolbar);

    frame.setLayout(new BorderLayout());
    panel.setLayout(new GridLayout(width, length));

    grid = new JLabel[width][length];

    panel.addMouseListener(this);

    for(int y=0; y<length; y++){

        for(int x=0; x<width; x++){

            int randomColor = rand.nextInt(5);
            ImageIcon icon = createImageIcon(buttonPics[randomColor]);

            grid[x][y] = new JLabel(icon);
            panel.add(grid[x][y]);

        }
    }

    frame.add(toolbar, BorderLayout.NORTH);
    frame.add(panel, BorderLayout.CENTER);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true); 

}

/*
    Finds URL for button images and returns it
*/
ImageIcon createImageIcon(String path) {

    URL imgURL = ColorGrid.class.getResource(path);

    if (imgURL != null) 
        return new ImageIcon(imgURL);
    else {
        System.err.println("Couldn't find file: " + path);
        return null;
    }

}

/*
    Adds buttons to the ButtonGroup and then add to Toolbar
*/
void addButtons(ButtonGroup bgroup, JToolBar toolbar) {
    JToggleButton button = null;

    //first button
    button = makeNavigationButton("circle_blue", PREVIOUS, "Back to previous something-or-other", "Previous");
    bgroup.add(button);
    toolbar.add(button);

    //second button
    button = makeNavigationButton("circle_Green", UP, "Up to something-or-other", "Up");
    bgroup.add(button);
    toolbar.add(button);

    //third button
    button = makeNavigationButton("circle_orange", NEXT, "Forward to something-or-other", "Next");
    bgroup.add(button);
    toolbar.add(button);

    button = makeNavigationButton("circle_red", NEXT, "Forward to something-or-other", "Next");
    bgroup.add(button);
    toolbar.add(button);

    button = makeNavigationButton("circle_yellow", NEXT, "Forward to something-or-other", "Next");
    bgroup.add(button);
    toolbar.add(button);

}

/*
    Called by the addButtons() method.

    Handles main button creation logic - finds the image and sets the command to the default string commands
*/
JToggleButton makeNavigationButton(String imageName, String actionCommand, String toolTipText, String altText) {
    //Look for the image.
    String imgLocation = "images/"
                         + imageName
                         + ".png";
    URL imageURL = ColorGrid.class.getResource(imgLocation);

    //Create and initialize the button.
    JToggleButton button = new JToggleButton();
    button.setActionCommand(actionCommand);
    button.setToolTipText(toolTipText);

    if (imageURL != null) {                      //image found
        button.setIcon(new ImageIcon(imageURL, altText));
    } else {                                     //no image found
        button.setText(altText);
        System.err.println("Resource not found: "
                           + imgLocation);
    }

    return button;
}

public void mouseEntered(MouseEvent e) {

    JPanel panel = (JPanel) getComponentAt(e.getPoint());

    if (panel != null) {
        System.out.println("Button entered!");
    }
}

public void mousePressed(MouseEvent e) {
    System.out.println("Mouse pressed!");
}

public void mouseReleased(MouseEvent e) {
    System.out.println("Mouse released!");
}

public void mouseExited(MouseEvent e) {
    System.out.println("Mouse exited!");
}

public void mouseClicked(MouseEvent e) {
    System.out.println("Mouse clicked!");
}


public static void main(String[] args) {
    new ColorGrid(4,4);//makes new ButtonGrid with 2 parameters
}

}

How can I fix this?

Answer 1

If you want to test for mouse entering a button, add a ChangeListener to the button's ButtonModel and test for isRollover()

Answer 2

I'm not sure you mean "button" as the only thing you're adding to your GridLayout is JLabels...

But basically, you need to register a MouseListener with each component individuallym for example...

for(int y=0; y<length; y++){

    for(int x=0; x<width; x++){

        int randomColor = rand.nextInt(5);
        ImageIcon icon = createImageIcon(buttonPics[randomColor]);

        grid[x][y] = new JLabel(icon);
        grid[x][y].addMouseListener(this);
        panel.add(grid[x][y]);

    }
}

You should also remove the panel.addMouseListener(this); call as this might just consfuse the issue...

Answer 3

well you are doing

panel.addMouseListener(this);

try changing it to

button.addMouseListener(this); 

in the addButtons method