Swap JPanels in an array of JPanels

Question

I am able to SWAP the panels but it is not good enough. For instance, if panel1 collides panel2, it swaps, but if the same collides panel3, panel3 also moves to panel1 location(which I don't want to happen). If there are about 10 panels, and if I want to swap panel1 with panel10 it is not possible with current logic. Can anyone please help me out.

Below is the code with the above logic:

import javax.swing.border.LineBorder;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class GDragAndDrop extends JFrame {
   public GDragAndDrop() {
      add(new op());
   }

   public static void main(String[] args) {
      GDragAndDrop frame = new GDragAndDrop();
      frame.setTitle("GDragAndDrop");
      frame.setSize(600, 600);
      frame.setLocationRelativeTo(null);// Center the frame
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
}

class op extends JPanel implements MouseListener, MouseMotionListener {
   JPanel p;
   Point pPoint;
   Point p1;
   Point p2;
   MouseEvent pressed;
   JPanel[] panels = new JPanel[3];

   public op() {
      int b = 3;
      int a = 0;
      for (int i = 0; i < b; i++) {
         panels[i] = new JPanel();
         panels[i].setBackground(Color.cyan);
         panels[i].setBorder(new LineBorder(Color.black));
         a = a + 20;
         panels[i].setPreferredSize(new Dimension(a, 400));
         panels[i].addMouseListener(this);
         panels[i].addMouseMotionListener(this);
         panels[i].setBorder(new LineBorder(Color.black));
         panels[i].setVisible(true);
         panels[i].add("Center", new JLabel("To Move" + i));
         this.add(panels[i]);
      }
   }

   public JPanel getPanelColliding(JPanel dragPanel) {
      Rectangle rDrag = dragPanel.getBounds();
      for (int i = 0; i < 3; i++) {
         if (panels[i] == dragPanel)
            continue;
         Rectangle r = panels[i].getBounds();
         if (r.intersects(rDrag)) {
            return panels[i];
         }
      }
      return null;
   }

   public void mousePressed(MouseEvent e) {
      int b = 3;
      for (int i = 0; i < b; i++) {
         if (e.getSource() == panels[i]) {
            pressed = e;
            p2 = panels[i].getLocation();
         }
      }
   }

   @Override
   public void mouseDragged(MouseEvent arg0) {
      int b = 3;
      for (int i = 0; i < b; i++) {
         if (arg0.getSource() == panels[i]) {
            pPoint = panels[i].getLocation(pPoint);
            int x = pPoint.x - pressed.getX() + arg0.getX();
            int y = pPoint.y - pressed.getY() + arg0.getY();
            if (getPanelColliding(panels[i]) != null) {
               JPanel DragP = new JPanel();
               DragP = getPanelColliding(panels[i]);
               p1 = getPanelColliding(panels[i]).getLocation(p1);
               int x1 = pPoint.x - pressed.getX() + arg0.getX();
               int y1 = pPoint.y - pressed.getY() + arg0.getY();
               panels[i].setLocation(x1, y1);
               DragP.setLocation(p2);
            } else
               panels[i].setLocation(x, y);
         }
      }
   }

   @Override
   public void mouseClicked(MouseEvent e) {
   }

   @Override
   public void mouseReleased(MouseEvent e) {
   }

   @Override
   public void mouseEntered(MouseEvent e) {
   }

   @Override
   public void mouseExited(MouseEvent e) {
   }

   @Override
   public void mouseMoved(MouseEvent e) {
   }
}

Answer 1

If you don't want to use drag-and-drop, and if your JPanels are in columns, then consider these suggestions:

• I've gotten this to work having the container JPanel (the one that holds the multiple column components) use a FlowLayout
• I've added the MouseAdapter as a MouseListener and MouseMotionListener to the container JPanel, not the column components.
• I obtained the selected column component by calling getComponentAt(mouseEvent.getPoint()) on the container JPanel. Of course check that it's not null.
• If the selected component is not null, then I set a selectedComponent variable with this component, and put a placeholder JLabel that has the same preferredSize in its place. I do this by removing all components from the container JPanel, and then re-adding them all back except for the selected component where I instead add the placeholder JLabel. I then call revalidate and repaint on the container.
• To drag the selected component, elevate it to the glassPane (i.e., add it to the glassPane).
• make the glassPane visible and give it a null layout.
• Drag the selected component in the glassPane simply by changing its location relative to the glassPane.
• On mouseReleased, find out what column component the mouse is over, again by using getComponentAt(...).
• Then remove all components from the container JPanel,
• and then add them all back in the desired order.
• Then again call revalidate and repaint on the container JPanel.

  ---

For example:

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridBagLayout;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.*;

public class SwapPanelEg extends JPanel {
   private static final long serialVersionUID = 1594039652438249918L;
   private static final int PREF_W = 400;
   private static final int PREF_H = 400;
   private static final int MAX_COLUMN_PANELS = 8;
   private JPanel columnPanelsHolder = new JPanel();

   public SwapPanelEg() {
      columnPanelsHolder.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));

      for (int i = 0; i < MAX_COLUMN_PANELS; i++) {
         int number = i + 1;
         int width = 20 + i * 3;
         int height = PREF_H - 30;
         columnPanelsHolder.add(new ColumnPanel(number, width, height));
      }

      MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
      columnPanelsHolder.addMouseListener(myMouseAdapter);
      columnPanelsHolder.addMouseMotionListener(myMouseAdapter);

      setLayout(new GridBagLayout());
      add(columnPanelsHolder);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private class MyMouseAdapter extends MouseAdapter {
      private JComponent selectedPanel;
      private Point deltaLocation;
      private JLabel placeHolder = new JLabel();
      private JComponent glassPane;

      @Override
      public void mousePressed(MouseEvent evt) {
         if (evt.getButton() != MouseEvent.BUTTON1) {
            return;
         }
         JPanel source = (JPanel) evt.getSource();
         selectedPanel = (JComponent) source.getComponentAt(evt.getPoint());

         if (selectedPanel == null) {
            return;
         }

         if (selectedPanel == source) {
            selectedPanel = null;
            return;
         }

         glassPane = (JComponent) SwingUtilities.getRootPane(source).getGlassPane();
         glassPane.setVisible(true);
         Point glassPaneOnScreen = glassPane.getLocationOnScreen();
         glassPane.setLayout(null);
         Point ptOnScreen = evt.getLocationOnScreen();
         Point panelLocOnScreen = selectedPanel.getLocationOnScreen();

         int deltaX = ptOnScreen.x + glassPaneOnScreen.x - panelLocOnScreen.x;
         int deltaY = ptOnScreen.y + glassPaneOnScreen.y - panelLocOnScreen.y;

         deltaLocation = new Point(deltaX, deltaY);

         Component[] allComps = source.getComponents();
         for (Component component : allComps) {
            source.remove(component);
            if (component == selectedPanel) {
               placeHolder.setPreferredSize(selectedPanel.getPreferredSize());
               source.add(placeHolder);
               selectedPanel.setSize(selectedPanel.getPreferredSize());
               int x = ptOnScreen.x - deltaLocation.x;
               int y = ptOnScreen.y - deltaLocation.y;
               selectedPanel.setLocation(x, y);
               glassPane.add(selectedPanel);
            } else {
               source.add(component);
            }
         }
         revalidate();
         repaint();

      }

      @Override
      public void mouseDragged(MouseEvent evt) {
         if (selectedPanel != null) {
            Point ptOnScreen = evt.getLocationOnScreen();

            int x = ptOnScreen.x - deltaLocation.x;
            int y = ptOnScreen.y - deltaLocation.y;
            selectedPanel.setLocation(x, y);
            repaint();
         }
      }

      @Override
      public void mouseReleased(MouseEvent evt) {
         if (evt.getButton() != MouseEvent.BUTTON1) {
            return;
         }
         if (selectedPanel == null) {
            return;
         }

         JComponent source = (JComponent) evt.getSource();

         Component[] allComps = source.getComponents();
         Component overComponent = (JComponent) source.getComponentAt(evt
               .getPoint());

         source.removeAll();

         if (overComponent != null && overComponent != placeHolder
               && overComponent != source) {
            for (Component component : allComps) {
               if (component == placeHolder) {
                  source.add(overComponent);
               } else if (component == overComponent) {
                  source.add(selectedPanel);
               } else {
                  source.add(component);
               }
            }
         } else {
            for (Component component : allComps) {
               if (component == placeHolder) {
                  source.add(selectedPanel);
               } else {
                  source.add(component);
               }
            }
         }
         revalidate();
         repaint();
         selectedPanel = null;
      }
   }

   private static void createAndShowGui() {
      SwapPanelEg mainPanel = new SwapPanelEg();

      JFrame frame = new JFrame("SwapPanelEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class ColumnPanel extends JPanel {
   private static final long serialVersionUID = 5366233209639059032L;
   private int number;
   private int prefWidth;
   private int prefHeight;

   public ColumnPanel(int number, int prefWidth, int prefHeight) {
      setName("ColumnPanel " + number);
      this.number = number;
      this.prefWidth = prefWidth;
      this.prefHeight = prefHeight;

      add(new JLabel(String.valueOf(number)));
      setBorder(BorderFactory.createLineBorder(Color.black));
      setBackground(Color.cyan);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(prefWidth, prefHeight);
   }

   public int getNumber() {
      return number;
   }

}

Answer 2

If you don't want to use Swing drag-and-drop, swap the content of the source and destination, as shown in this JLayeredPane example and variation.