Question

As you see these picture, the background grid lines and black rectangle are not updated after the menu item is closed. How can I update it? In C# there is an event handler to make it updated automatically, but I am newbie to Java swing GUI application.

Here is the code:

public void paint(Graphics g) {

  super.paintComponents(g); 

  MainDisplayForm mD = new MainDisplayForm();           


  Graphics2D g2 = (Graphics2D) g;  

  g2.setColor(Color.BLACK);
  int gridWidth = 1240;
  int gridHeight = 400;      
  g2.fillRect(20, 50, gridWidth, gridHeight);


  g2.setColor(Color.darkGray);

  paintGrid(g2,gridWidth, gridHeight);

  g2.setColor(Color.red);
  Line2D line = new Line2D.Float(20, 50, 250, 260);               
  g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
  //g2.draw(line); //pending       

  g2.dispose();

}

private void paintGrid(Graphics g, int gridWidth, int gridHeight)
{

  for(int i=20; i<gridWidth+20; i=i+10)
  {      
      g.drawLine(i, 50, i, gridHeight+49);          
  }      

  for(int i=50; i<gridHeight+50; i=i+10)
  {      
      g.drawLine(20, i, 1259, i);          
  }      
}

//Thanks for comments!! Here is the event handler to add.
This must be added to every memu item drawn over the grid

private void jMenu2MenuDeselected(javax.swing.event.MenuEvent evt) {
    repaint();
}

Answer 1

When the menu is closed call reprint to the window.

Don’t call paint(getGraphics()). Instead call repaint() because this informs the super component that it needs to redraw as well.