Question

I’m drawing lines on a JPanel using a paint component and graphics 2D, but the background of the JPanel is set to a grid which is drawn when the user enters some dimensions. How do I clear the lines drawn on the JPanel when a button is clicked but regenerate a fresh panel again with the grid lines drawn? With the action event method for the clear button, I’ve tried using repaint(), removeAll() and creating a new instance of the JPanel but none of that seems to work.

Here is the code for the class with the main Panel and button functions:

package floorplan;

/**
*
* @author xodkx
*/


import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.SwingUtilities;


public class FloorPlan extends JFrame 
{

private JPanel backPanel = new JPanel();
private JPanel toolsPanel = new JPanel();
private JFrame chooseFurniture;
private JFrame chooseFixture;
private JFrame chooseFramework;
private JButton furnitureButton = new JButton();
private JButton fixturesButton = new JButton();
private JButton frameworkButton = new JButton();
private JButton deleteButton = new JButton();
private JButton saveButton = new JButton();
private JButton clearButton = new JButton();
private JButton closeButton = new JButton();
private JRadioButton wall = new JRadioButton("Wall");
private JRadioButton door = new JRadioButton("Door");
private JRadioButton window = new JRadioButton("Window");


Floor floor = new Floor();

public FloorPlan()
{
     super("Floor Plan Generator");  
     createWindow();
     buttonFunctions();
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     pack();
     setVisible(true);
}

private void createWindow()
{
  backPanel.setLayout(new BorderLayout());
  backPanel.setBorder(BorderFactory.createEmptyBorder(200, 200, 200, 200));
  GridLayout panelLayout = new GridLayout();
  frameworkButton.setText("Framework");
  fixturesButton.setText("Fixtures");
  furnitureButton.setText("Furniture");
  deleteButton.setText("Delete");
  saveButton.setText("Save");
  clearButton.setText("Clear");

  add(backPanel, BorderLayout.CENTER);
  backPanel.add(toolsPanel, BorderLayout.NORTH);
  backPanel.add(floor, BorderLayout.CENTER);
  backPanel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
  toolsPanel.add(frameworkButton);
  toolsPanel.add(fixturesButton);
  toolsPanel.add(furnitureButton);
  toolsPanel.add(deleteButton);
  toolsPanel.add(saveButton);
  toolsPanel.add(clearButton);
  add(backPanel); 
}


private void buttonFunctions()
{
    frameworkButton.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(final ActionEvent e)
        {
           chooseFramework = new JFrame("Pick A Framework");
           chooseFramework.setSize(250,250);
           chooseFramework.setLayout(new GridLayout(4,1));
           chooseFramework.add(wall);
           chooseFramework.add(door);
           chooseFramework.add(window);
           chooseFramework.add(closeButton);
           closeButton.setText("Close");


           wall.addActionListener(new ActionListener() 
          {
                @Override
                public void actionPerformed(ActionEvent e) 
          {

               floor.setFramework(Framework.WALL);



        }});

            door.addActionListener(new ActionListener() 
          {
                @Override
                public void actionPerformed(ActionEvent e) 
          {

               floor.setColor(Color.RED);
               floor.setFramework(Framework.DOOR);


        }});

            window.addActionListener(new ActionListener() 
          {
                @Override
                public void actionPerformed(ActionEvent e) 
          {
               floor.setColor(Color.BLUE);
               floor.setFramework(Framework.WALL);


        }});

           closeButton.addActionListener(new ActionListener() 
           {
                @Override
            public void actionPerformed(ActionEvent e) 
            {
               chooseFramework.setVisible(false);

            }
           });

            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            pack();
            chooseFramework.setVisible(true);
        }
    });

    furnitureButton.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(final ActionEvent e)
        {
           chooseFurniture = new JFrame("Pick Furniture to add");
           chooseFurniture.setSize(250,250);
           chooseFurniture.setLayout(new GridLayout(4,1));
           chooseFurniture.add(closeButton);
           closeButton.setText("Close");

           closeButton.addActionListener(new ActionListener() 
           {
                @Override
            public void actionPerformed(ActionEvent e) 
            {
               chooseFurniture.setVisible(false);
            }
           });

            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            pack();
            chooseFurniture.setVisible(true);
        }
    });

    fixturesButton.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(final ActionEvent e)
        {
           chooseFixture = new JFrame("Pick Furniture to add");
           chooseFixture.setSize(250,250);
           chooseFixture.setLayout(new GridLayout(4,1));
           chooseFixture.add(closeButton);
           closeButton.setText("Close");

           closeButton.addActionListener(new ActionListener() 
           {
                @Override
            public void actionPerformed(ActionEvent e) 
            {
               chooseFixture.setVisible(false);
            }
           });

            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            pack();
            chooseFixture.setVisible(true);
        }
    });

      **clearButton.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(final ActionEvent e)
        {  
          **//THIS IS WHERE I WANT TO CLEAR THE JPANEL WHEN THIS BUTTON IS CLICKED**  
        }
   });**
}    
public static void main(String[] args) 
{
    SwingUtilities.invokeLater(new Runnable()
     {

        @Override
          public void run()
          {
            FloorPlan floorPlan = new FloorPlan();
          }

     });
}
}

Here is the class that does all the graphics stuff and draws onto the JPanel

package floorplan;

/**
*
* @author xodkx
*/

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.image.BufferedImage;
import java.awt.event.MouseListener;

public class Floor extends JPanel implements MouseListener, MouseMotionListener
{


private static final int WIDTH = Integer.parseInt(JOptionPane.showInputDialog("Please    
                                                   enter the width of your room"));
private static final int LENGTH = Integer.parseInt(JOptionPane.showInputDialog("Please 
                                                 enter the width of your room"));
private static final Color BACKGROUND = Color.WHITE;
private static final Color INITIAL_COLOUR = Color.BLACK;
private static final Framework INITIAL_FRAMEWORK = Framework.WALL;

private MouseState state = MouseState.IDLE;
private Framework frameworkType = INITIAL_FRAMEWORK;
private Color colour = INITIAL_COLOUR;


private Point start = null;
private Point end = null;
private Point startpt = null;
private Point endpt = null;

private BufferedImage bufImage = null;


public Floor()
{
    setPreferredSize(new Dimension(LENGTH,WIDTH));
    setBackground(Color.white);
    setBorder(BorderFactory.createLineBorder (Color.black, 5));

    this.addMouseListener(this);
    this.addMouseMotionListener(this);

}

public void setColor(Color color)
{
    colour = color;

}

public void setFramework(Framework framework)
{
    frameworkType = framework;
}

@Override
public void paintComponent(Graphics g)
{
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D)g;
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
      RenderingHints.VALUE_ANTIALIAS_ON);

    if(bufImage == null)
    {
        int h = this.getHeight();
        int w = this.getWidth();
        bufImage = (BufferedImage)this.createImage(h,w);
        Graphics2D gc = bufImage.createGraphics();
        gc.setColor(BACKGROUND);
        gc.fillRect(0, 0, w, h);
    }


    g2.drawImage(bufImage,null,0,0);

    drawGrid(g2);

    if(state == MouseState.DRAGGING)
    {
        createComponent(g2);
    }
}

public void drawGrid(Graphics g2)
{
    int gridDivisions = 20;
    int divisionSize = WIDTH/gridDivisions;
    int grid = WIDTH*LENGTH;

    g2.setColor(Color.lightGray);

    for(int i=1; i<grid; i++)
    {
        int x = i * divisionSize;
        g2.drawLine(x,0,x,getSize().height);
    }

    for(int i=1; i<grid; i++)
    {
        int y = i*divisionSize;
        g2.drawLine(0,y,getSize().width,y);
    }
}


public void createComponent(Graphics2D g2)
{
    g2.setColor(colour);

    switch (frameworkType)
    {
        case WALL:
            g2.setStroke(new BasicStroke(5));
            g2.drawLine(start.x, start.y, end.x,end.y);
            break;

        case DOOR:
            g2.setStroke(new BasicStroke(5));
            g2.drawLine(start.x, start.y, end.x,end.y);
            break;

        case WINDOW:
            g2.setStroke(new BasicStroke(5));
            g2.drawLine(start.x, start.y, end.x,end.y);
            break;


        default:
            g2.drawString("test", 10, 20);
            break;
    }
}


@Override
public void mousePressed(MouseEvent e)
{
    state = MouseState.DRAGGING;
    start = e.getPoint();
    end = start;
}

@Override

public void mouseDragged(MouseEvent e)
{

    state = MouseState.DRAGGING;
    end = e.getPoint();
    this.repaint();

}

@Override
public void mouseReleased(MouseEvent e)
{
    end = e.getPoint();
    if(state == MouseState.DRAGGING)
    {
        state = MouseState.IDLE;
        createComponent(bufImage.createGraphics());
        this.repaint();
    }
}



@Override
public void mouseClicked(MouseEvent e)
{

}

@Override
public void mouseEntered(MouseEvent e)
{

}

@Override
public void mouseExited(MouseEvent e)
{

}



@Override
public void mouseMoved(MouseEvent e)
{

}

}

Answer 1

It is not clear exactly how do you want to incorporate the logic of displaying the grid. Here is an example how to toggle it just to give you the idea. In Floor class add boolean flag that controls whether the grid is displayed or not. Then in Floor.paintComponent() draw grid based on the value of this boolean flag. Changing the flag’s value should trigger a repaint. Then, change the value of this flag from FloorPlan class, in response to an action or some other program logic. Here is a simple implementation that toggles grid when clear button is clicked :

Floor class:

private boolean displayGrid = true;

public boolean isDisplayGrid() {
    return displayGrid;
}
public void setDisplayGrid(boolean displayGrid) {
    this.displayGrid = displayGrid;
    repaint();
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    ...
    if (displayGrid)
        drawGrid(g2);
}

FloorPlan class:

clearButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(final ActionEvent e) {
        floor.setDisplayGrid(!floor.isDisplayGrid());
    }
});

EDIT:

Seems that I totally misinterpreted your question. If I understand correctly you want to clear the drawings upon a button click. Looks like all the drawings are done on the bufImage in the Floor class. Simply reset this image, ie:

Floor class:

public void clear() {
    bufImage.flush();
    bufImage = null;
    repaint();
}

FloorPlan class:

clearButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(final ActionEvent e) {
        floor.clear();
    }
});