Trying to add a dynamically positioned image to JPanel when a button is clicked

Question

I am trying to add / draw a separate Graphics object to an existing JPanel. I generate 10 initial graphic objects randomly and place them on the panel, but I would like to add additional drawn objects once, a random size and place them as initial 10.

The AddNewDrawItem class does not currently create a new Graphics object.

Thanks for the input.

import javax.swing.*; import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.util.Random; public class Painter{ private DrawingPanel dp = new DrawingPanel(); //constructor public Painter(){ buildGUI(); } private void buildGUI(){ JFrame frame = new JFrame(); frame.setLayout(new BorderLayout()); frame.setTitle("Paint drawing demonstration"); JPanel headerPanel = new JPanel(); headerPanel.add(new JLabel("The drawing panel is below")); JButton addNew = new JButton("Add New Graphic"); addNew.addActionListener(new addNewClickHandler()); headerPanel.add(addNew); frame.add(BorderLayout.NORTH,headerPanel); frame.add(BorderLayout.SOUTH,this.dp); frame.pack(); frame.setVisible(true); } class DrawingPanel extends JPanel { public void paintComponent(Graphics g) { super.paintComponent(g); this.setBackground(Color.white); int x, posx, posy, width, height; for(x=0;x<=10;x++){ //even number differentiation if(x % 2 == 0){ g.setColor(Color.red); }else{ g.setColor(Color.blue); } Random rand = new Random(); posx = rand.nextInt(300); posy = rand.nextInt(300); width = rand.nextInt(40); height = rand.nextInt(40); //System.out.println("the ran x pos is: " + posx); g.fillRect(posx, posy, width, height); }//end for }//end paintComponent public Dimension getPreferredSize() { return new Dimension(400,400); } }// end DrawingPanel private class addNewClickHandler implements ActionListener{ public void actionPerformed(ActionEvent e){ System.out.print("in addNew_click_handler click handler");//trace debug AddNewDrawItem newItem = new AddNewDrawItem(); newItem.repaint(); System.out.print("after repaint() in addNew_click_handler click handler");//trace debug } } class AddNewDrawItem extends JPanel { public void paintComponent(Graphics g) { super.paintComponent(g); this.setBackground(Color.white); int posx, posy, width, height; Random rand = new Random(); posx = rand.nextInt(300); posy = rand.nextInt(300); width = rand.nextInt(40); height = rand.nextInt(40); g.setColor(Color.cyan); g.fillRect(posx, posy, width, height); }//end paintComponent }//end AddNewDrawItem public static void main(String args[]){ new Painter(); } }//end class Painter 

Answer 1

You have some problems with your code, one of which is that you have program logic in your paintComponent method: the code randomly changes the values ​​displayed in this method, which means that your display will change when it is copied, do you want to you this or not. To make sure this is the case, try resizing your GUI and you will see some psychedelic changes in the drawn red and blue rectangles.

Now about your current problem, solving this is similar to solving the problem described above. I suggest...

• what you create ArrayList<Rectangle2D> ,
• that you create your random rectangles in your class constructor so that they are created only once and then put them in the ArrayList above.
• so that you iterate over this ArrayList into your JPanel paintComponent method, drawing them when you go. So paintComponent does nothing but paint, which should be what it should be,
• that you create an object derived from MouseAdapter and add it as MouseListener and MouseMotionListener to your DrawingPanel
• that you use the listener above to create a new Rectangle2D object, and when this is done add it to the ArrayList and redraw the call to the DrawingPanel
• that you activate the mouse adapter through your button action listener.

I will dwell on this, but I think you understand this idea, and if you do not, ask any questions that may arise.