java delete a component

Question

Current I can add a bunch of customed component objects to the JPanel by pressing "add" JButton. I also got a "delete" JButton which I wish to do the opposite of "add".

My intention is that I can select a component with a mouse and click the delete button and pressto!, the component is gone.

I hook a MouseListener to the panel, and use MouseEvent, e.getComponent() to get w/e current component the mouse clicks on. So if it returns a custom component then a variable "private myComponent current" (already set to null) will point to that component. Then I can just click on "delete" button to remove it. An actionListener already added in "delete" button and in the body it calls this.remove(current) (if current is not null).

However, this doesn't work as I can't remove a component! Any pointer?

If there is an elegant way to managing add/remove components please suggest!

public class MainDisplayPanel extends JPanel implements ActionListener, MouseListener{

private JButton newClassButton;
private JButton deleteButton;
private Resizable current;
private Resizable resizer;
public MainDisplayPanel(LayoutManager layout) {
    super(layout);

    newClassButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
            addResizer();
     }          
    });

    deleteButton = new JButton("Delete");
    deleteButton.addActionListener(this);
    this.addMouseListener(this);
    this.add(newClassButton);
    this.add(deleteButton);

}
public void addResizer() {
    //JPanel panel = new JPanel();
    //panel.setBackground(Color.white);
     resizer = new Resizable( new ClassBox());
    this.add(resizer);
    this.revalidate();
    this.repaint();
}

public void actionPerformed(ActionEvent e) {
          if(current!=null)
          {
              this.remove(current);
              this.revalidate();
              this.repaint();

          }
}

public void mouseClicked(MouseEvent e) {
    System.out.println(e);
            Component component = e.getComponent();

            if(component instanceof Resizable)
                current= (Resizable) e.getComponent();

}


    public static void main(String[] args) {
    JFrame jframe = new JFrame();
    jframe.add(new MainDisplayPanel(null));
    jframe.setSize(new Dimension(600,400));
    jframe.setVisible(true);
    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

} Doh!

Now, in the addResizer() method. Every time I press the add button to add a new Resizable object, what'd happen to the previously added objects? I'm certain that they become null because resizer variable no longer referring to it them??? Even if this is the case, they are still displayed on the panel...And if I pressed delete only the newly added Resizable object gets removed. So am I on the right track here?

Edit: to sum up my problem, I hooked the MouseListener to wrong object. It should be Resizable object instead of the panel. Therefore, variable current is always null.

Answer 1

it very crazy idea, but everything is possible, but

1) in case that you Layed JComponent by using some of LayoutManager you can remove JComponents from Container, and thenafter you must/have to call revalidate() + repaint(), but this actions has side effect -> ReLayout Container and then Container's contents could be look very ***

2) in case that you layed Container with AbsoluteLayout, that should be maybe nicest but question is what with emtpy space inside Container

there is very easy way how to do it, you need to add JPopupMenu to the Container,

• on RightMouseClick you have to finding JComponent under the MouseCursor

• then call Container#remove(myComponent), thenafter you have to call revalidate() + repaint() for refresh GUI

or is same for me

• call myComponent.setVisible(false), no re-layout, no revalidate + repaint, JComponent waiting on same place for (eventually) reusing

• excelent thread about how to LayoutManagers add/remove JComponents + revalidate + repaint

Answer 2

Your problem is your MouseLisetener. You are listening to the MainDisplayPanel, and so when you click on the JPanel, the MouseEvent#getComponent method returned by, e, in your mousePressed method will return the MainDisplayPanel instance since that is what is being listened to, not the Resizable instance that is under the mouse.

Solutions include:

• creating one MouseListener object and adding this same object to each Resizable as a MouseListener for the Resizable, or
• using your current set up, but hold your Resizable's in an ArrayList and then iterating through the array list in the mousePressed method to see if any Resizable has been clicked by using the componentAt(...) method.

Note that I had to create my own SSCCE to solve this. Again in the future, please do us all a favor and do this for us as it really is in your and our best interest, and shows that you respect our time and our help.

Edit 1
My SSCCE:

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

import javax.swing.*;

@SuppressWarnings("serial")
public class MainDisplayPanel extends JPanel {
   private static final int RESIZABLE_COUNT = 40;
   private JButton deleteButton;
   private Resizable current;
   private Resizable resizer;
   private List<Resizable> resizableList = new ArrayList<Resizable>();

   public MainDisplayPanel(LayoutManager layout) {
      super(layout);

      deleteButton = new JButton("Delete");
      deleteButton.addActionListener(new ActionListener() {
         @Override
         public void actionPerformed(ActionEvent e) {
            deleteButtonActionPerformed(e);
         }
      });
      this.addMouseListener(new MyMouseAdapter());
      this.add(deleteButton);

      for (int i = 0; i < RESIZABLE_COUNT; i++) {
         addResizer();
      }
   }

   private void deleteButtonActionPerformed(ActionEvent e) {
      if (current != null) {
         this.remove(current);
         resizableList.remove(current);
         current = null;
         this.revalidate();
         this.repaint();
      }
   }

   public void addResizer() {
      resizer = new Resizable();
      this.add(resizer);
      resizableList.add(resizer);
      this.revalidate();
      this.repaint();
   }

   private class MyMouseAdapter extends MouseAdapter {

      @Override
      public void mousePressed(MouseEvent e) {
         current = null;
         Component c = getComponentAt(e.getPoint());
         for (Resizable resizable : resizableList) {
            if (resizable == c) {
               current = resizable;
               resizable.setFill(true);
            } else {
               resizable.setFill(false);
            }
         }
      }
   }

   public static void main(String[] args) {
      JFrame jframe = new JFrame();
      // !! jframe.add(new MainDisplayPanel(null));
      jframe.add(new MainDisplayPanel(new FlowLayout()));
      jframe.setSize(new Dimension(600, 400));
      jframe.setVisible(true);
      jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   }

}

@SuppressWarnings("serial")
class Resizable extends JPanel {

   private static final int RESIZE_WIDTH = 50;
   private static final int RESIZE_HEIGHT = 40;
   private static final int THICKNESS = 5;
   private static final Color FILL_COLOR = Color.pink;

   public Resizable() {
      Random rand = new Random();

      // different color border so we can see that it was the clicked one that was deleted.
      Color color = new Color(
               rand.nextInt(255), 
               rand.nextInt(255), 
               rand.nextInt(255));
      setBorder(BorderFactory.createLineBorder(color, THICKNESS));
   }

   @Override // so we can see it
   public Dimension getPreferredSize() {
      return new Dimension(RESIZE_WIDTH, RESIZE_HEIGHT);
   }

   public void setFill(boolean fill) {
      Color fillColor = fill ? FILL_COLOR : null;
      setBackground(fillColor);
      repaint();
   }

}

Answer 3

I believe the problem is you need to force Swing to layout the components again after removing one. After you remove(current), call revalidate().