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?
On
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.
You can use the
mouseDragged()method of theMouseMotionListenerin conjunction with themousePressed()method of theMouseListener.The
mousePressed()method will handle a simple click without movement, andmouseDragged()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.