Alberto Alberto - 3 months ago 24
Java Question

How to make an event in a matrix of JButtons?

I'm trying to create a

MouseListener
. When I hover a
JButton
, I want it to change its background color and the next
JButton
s in the array. For example, when I hover
JButton[0][0]
, it changes the background of
JButton[0][0]
,
JButton[1][0]
,
JButton[2][0]
and so on.

Here is how I create the
JButton
array:

for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++) {
btn[i][j] = new JButton();
btn[i][j].addMouseListener(this);
btn[i][j].setBackground(Color.black);
panel.add(btn[i][j]);
}
}


And its
MouseListener
:

@Override
public void mouseEntered(MouseEvent me) {
JButton event = (JButton) me.getSource();
int i = 0;
int j = 0;
btn[i][j] = event;
btn[i][j].setBackground(Color.blue);
}

@Override
public void mouseExited(MouseEvent me) {
JButton event = (JButton) me.getSource();
int i = 0;
int j = 0;
btn[i][j] = event;
btn[i][j].setBackground(Color.black);

}


I have tried doing
btn[i+1][j].setBackground(Color.black);
and it sets blue
[1][0]
,
[2][0]
... but not
[i+1][j]
.

There are no errors when I run my program.

Here

The picture above shows what I'm trying to do.

Answer

The method you are looking for is called Component.dispatchEvent(AWTEvent e), with that I came up with a one-dimensional example:

package scratch.pad.ui;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.*;
import java.util.List;

/**
 * Propagate event to neighbor buttons
 */
public class EventPropagation extends JFrame {

    private List<JButton> buttons = new ArrayList<>();

    private class MouseEventPropagationListener extends MouseAdapter {

        // The event source, for controlling the propagation of the event.
        // To prevent infinite loop, we only dispatch the event to targets when
        // e.getSource() == this.source;
        private JButton source;

        // Targets to propagate the event.
        private java.util.List<JButton> targets;

        public MouseEventPropagationListener(JButton source, JButton ... targets) {
            this.source = source;
            this.targets = Arrays.asList(targets);
        }

        @Override
        public void mouseEntered(MouseEvent e) {
            super.mouseEntered(e);
            // Use this.source because e.getSource() could be different.
            this.source.setBackground(Color.WHITE);
            dispatchEvent(e);
        }

        @Override
        public void mouseExited(MouseEvent e) {
            super.mouseExited(e);
            this.source.setBackground(Color.BLACK);
            dispatchEvent(e);
        }

        private void dispatchEvent(MouseEvent e) {
            if (e.getSource() == source) {
                for (JButton target : targets) {
                    target.dispatchEvent(e);
                }
            }
        }
    }

    public EventPropagation() throws HeadlessException {

        final int n = 10;

        this.setTitle("Event propagation test");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.getContentPane().setLayout(new FlowLayout());

        this.setSize(300, 300);

        this.setResizable(false);

        // Create the buttons
        for (int i = 0; i < n; i++) {
            JButton btn = new JButton("Button " + i);
            btn.setBackground(Color.BLACK);
            this.buttons.add(btn);
            this.getContentPane().add(btn);
        }

        // Setup propagation:
        for (int i = 0; i < n; i++) {
            JButton btn = this.buttons.get(i);

            MouseEventPropagationListener listener = new MouseEventPropagationListener(btn, getNeighbors(i));
            btn.addMouseListener(listener);
        }
    }

    private JButton [] getNeighbors(int i) {
        List<JButton> neighbors = new ArrayList<>();

        if (i > 0) neighbors.add(this.buttons.get(i-1));
        if (i < this.buttons.size() - 1) neighbors.add(this.buttons.get(i + 1));

        return neighbors.toArray(new JButton[0]);
    }

    public static void main(String [] args) {
        EventPropagation ep = new EventPropagation();
        ep.setVisible(true);
    }
}
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