如何在jlayeredpane Java中画线

Question

I want to draw line in my jLayeredPane and this is my project from netbeans.

https://drive.google.com/file/d/0B6e6jjVl5-sCMkJFcEI3MkZEZ1E/view

I have problem when i clicked my button why i can't draw line in my jlayeredpane??where's my wrong with this code?

I want to draw some line in my jlayeredpane when click button draw.I try to add jlayerpane1.add some component.and i set this for visible.

how to fix it?

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    jLayeredPane1.add(new JComponent(){                                   
     ArrayList<Shape> linesList = new ArrayList<Shape>();
    private Shape line = null;
    {
    MouseAdapter mouseAdapter = new MouseAdapter(){
                @Override
        public void mousePressed (MouseEvent e){                       
        line = new Line2D.Double(e.getPoint(), e.getPoint());
        linesList.add(line);
        repaint();
        }
                @Override
        public void mouseDragged(MouseEvent e){
        Line2D shape =(Line2D)line;
        shape.setLine(shape.getP1(), e.getPoint());
        repaint();
        }
                @Override
        public void mouseReleased(MouseEvent e){
        line = null;
        repaint();
        }
    };
    addMouseListener(mouseAdapter);
    addMouseMotionListener(mouseAdapter);
    }
        @Override
    protected void paintComponent(Graphics g){
    Graphics2D g2d = (Graphics2D) g;
    g2d.setPaint(Color.BLUE);
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    for(Shape content : linesList){
        g2d.draw(content);
    }
  }          
    });
    jLayeredPane1.setVisible(true); // set for visible
}

Answer 1

A JLayeredPane uses a null layout. So when you add your custom painting panel to the layered pane you need to give the panel a size otherwise the size is (0, 0) so there is nothing to paint.

So the code should be something like:

JPanel panel = new CustomPaintingPanel();
panel.setSize(300, 300);
layeredPane.add(panel, ...);
frame.add(layeredPane);