在Graphics2D类中绘制直线拖放

Question

How can I draw a straight line on a drag and drop, that there was only one line and moved around?

My code:

panelPaint.addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    point1 = e.getPoint();
                }
            });
            panelPaint.addMouseMotionListener(new MouseMotionAdapter() {
                @Override
                public void mouseDragged(MouseEvent e) {
                    point2 = e.getPoint();

                    g2.draw(new Line2D.Double(point1, point2));

                    panelPaint.repaint();
                }
            });

Current effect:

Answer 1

Looks like you are drawing to a BufferedImage or something. You should not be doing painting using a Graphics object in the mouse event.

Instead you should be doing custom painting on a panel and override the paintCompnent(...) method. Your paintComponent() method should look like:

@Override
protected void paintComponent(Grapahics g)
{
    super.paintComponent(g);

    // custom painting here
    g.drawLine(...);

}

The first statement will clear the background. The next statement will draw the line between your starting/ending points.

Check out Custom Painting Approaches for more information and examples. The example will dynamically draw a Rectangle as you drag the mouse, but the concept is the same for a single line.