So I have a JPanel that is populated by the contents of a 2D array. I have a mouse listener which changes the colour of a cell when pressed. My question is, is it possible to have the user drag the mouse over a line of cells and colour them all in succession? I have looked into mouse motion listener but this doesn't seem to help.
Any ideas?
You can use the mouseDragged() method of the MouseMotionListener in conjunction with the mousePressed() method of the MouseListener.
The mousePressed() method will handle a simple click without movement, and mouseDragged() will handle any dragging done. I combined the code I wrote for my answer to your original question here to better clarify what everything does, and a response on your other question would be very much appreciated.
package stackoverflow.answers;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class JPanelPaint {
JPanel panel;
JFrame frame;
BufferedImage image;
public JPanelPaint() {
image = new BufferedImage(50, 50, BufferedImage.TYPE_INT_ARGB);
for (int i = 0; i < image.getWidth(); i++) {
for (int j=0; j < image.getHeight(); j++) {
/* I'm just initializing the image with an arbitrary color (white in this case), you can easily change this. */
image.setRGB(i, j, new Color((int)(255 ), (int)(255 ), (int)(255 )).getRGB());
}
}
frame = new JFrame("JPanel Paint");
panel = new JPanel() {
@Override
public void paint(Graphics g) {
super.paint(g);
Rectangle rect = g.getClipBounds();
g.setColor(Color.white);
g.fillRect(rect.x, rect.y, rect.width, rect.height);
for (int i = 0; i < image.getWidth(); i++) {
for (int j=0; j < image.getHeight(); j++) {
/* Set the color of the "quadpixel" to that of the original cell on the image. */
g.setColor(new Color(image.getRGB(i, j)));
g.fillRect(j*4, i*4, 4, 4);
}
}
}
};
panel.addMouseListener(new MouseListener() {
@Override
public void mouseClicked(MouseEvent arg0) { }
@Override
public void mouseEntered(MouseEvent arg0) { }
@Override
public void mouseExited(MouseEvent arg0) { }
@Override
public void mousePressed(MouseEvent arg0) {
/* Y and X are swapped, just a quirk in the JRE */
/* I'm just setting the pixel with an arbitrary color (black in this case), you can easily change this. */
image.setRGB(arg0.getY() / 4, arg0.getX() / 4, new Color(0, 0, 0).getRGB());
panel.repaint();
}
@Override
public void mouseReleased(MouseEvent arg0) { }
});
panel.addMouseMotionListener(new MouseMotionListener() {
@Override
public void mouseDragged(MouseEvent arg0) {
/* Y and X are swapped, just a quirk in the JRE */
/* I'm just setting the pixel with an arbitrary color (black in this case), you can easily change this. */
image.setRGB(arg0.getY() / 4, arg0.getX() / 4, new Color(0, 0, 0).getRGB());
panel.repaint();
}
@Override
public void mouseMoved(MouseEvent arg0) { }
});
panel.setPreferredSize(new Dimension(200, 200));
frame.add(panel);
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
panel.repaint();
}
public static void main(String[] args) {
new JPanelPaint();
}
}
You don't need the mouse listeners if you extend JPanel. Just enable mouse events then override the component's mouse event handlers. The general logic is:
if mouse pressed {
dragging = true
begin drag
}
if mouse dragged and dragging == true {
process drag
}
if mouse released and dragging == true {
dragging = false
finalize drag
}
Here is an example:
import java.awt.AWTEvent;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class DragTest {
// example JPanel. click and drag on it to create lines.
static class DragPanel extends JPanel {
private static final long serialVersionUID = 1L;
static class Line {
int x1, y1, x2, y2;
}
private final List<Line> lines = new ArrayList<Line>();
private Line draggedLine; // null if not dragging
public DragPanel() {
// enable mouse event processing even if no listeners are registered
enableEvents(AWTEvent.MOUSE_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK);
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLACK);
g.fillRect(0, 0, getWidth(), getHeight());
// draw saved lines
g.setColor(Color.WHITE);
for (Line line : lines)
g.drawLine(line.x1, line.y1, line.x2, line.y2);
// draw currently active line if there is one
if (draggedLine != null) {
g.setColor(Color.RED);
g.drawLine(draggedLine.x1, draggedLine.y1, draggedLine.x2, draggedLine.y2);
}
}
// does the work; since motion and press/release are all MouseEvent,
// we can just direct MouseEvents here from the event handler overrides
// and handle based on event ID.
private void handleMouseEvent(MouseEvent e) {
if (e.getID() == MouseEvent.MOUSE_PRESSED && e.getButton() == MouseEvent.BUTTON1) {
// begin drag by initializing a new Line at mouse position
if (draggedLine == null) {
draggedLine = new Line();
draggedLine.x1 = draggedLine.x2 = e.getX();
draggedLine.y1 = draggedLine.y2 = e.getY();
e.consume();
}
} else if (e.getID() == MouseEvent.MOUSE_DRAGGED) {
// if drag in progress, update line endpoint
if (draggedLine != null) {
draggedLine.x2 = e.getX();
draggedLine.y2 = e.getY();
e.consume();
}
} else if (e.getID() == MouseEvent.MOUSE_RELEASED && e.getButton() == MouseEvent.BUTTON1) {
// if drag in progress, accept new line and end drag
if (draggedLine != null) {
draggedLine.x2 = e.getX();
draggedLine.y2 = e.getY();
lines.add(draggedLine);
draggedLine = null;
e.consume();
}
}
if (e.isConsumed())
repaint();
}
@Override
public void processMouseMotionEvent(MouseEvent e) {
handleMouseEvent(e); // pass to our handler, may consume event
super.processMouseMotionEvent(e); // in case there are registered listeners
}
@Override
public void processMouseEvent(MouseEvent e) {
handleMouseEvent(e); // pass to our handler, may consume event
super.processMouseEvent(e); // in case there are registered listeners
}
}
public static final void main(String[] args) {
JFrame frame = new JFrame("Panel Drag Example");
frame.getContentPane().add(new DragPanel());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(640, 480);
frame.setVisible(true);
}
}
Extending JPanel is usually a better idea than adding listeners with inline classes because it gives you a fully self-contained reusable component.
