移动时如何在另一个JPanel上显示一个JPanel？

Question

I have created a card game which allows the users to move the cards, which are JPanels, on top of each other. However, I noticed that if I attempt to move a card to another cards exact location (ie on top of it), that card will not always be displayed on top of that card.

For example, lets say we have 5 cards, which where built in order.

If move card1 to card2's location, then card1 will appear on top of card2. However, if I tried to move card5 to card3's location, then card5 will appear underneath card3.

How can can I make is so that the last card that I move will be the one on top?

Answer 1

However, I noticed that if I attempt to move a card to another cards exact location (ie on top of it), that card will not always be displayed on top of that card.

This sounds related to the Z-Ordering of components. Basically the default behaviour for Swing is that the last component added to a panel is painted first.

So you need to change the Z-Order when you add the card on the panel. You are probably using code like:

 panel.add( card );

The easy solution is to use:

panel.add(0, card);

Or, when you handle the mousePressed() event when you click on the card your would use:

Component child = event.getComponent();
Component parent = child.getParent();
parent.setComponentZOrder(child, 0);

You may also want to look at the Overlap Layout which explains Z-Ordering a little more and provides a layout manager that can allow you to stack cards.

Answer 2

For this purpose card layout is your friend.

How to use card layout https://docs.oracle.com/javase/tutorial/uiswing/layout/card.html

Example uses:

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

public class CardLayoutDemo implements ItemListener {
    JPanel cards; //a panel that uses CardLayout
    final static String BUTTONPANEL = "Card with JButtons";
    final static String TEXTPANEL = "Card with JTextField";

    public void addComponentToPane(Container pane) {
        //Put the JComboBox in a JPanel to get a nicer look.
        JPanel comboBoxPane = new JPanel(); //use FlowLayout
        String comboBoxItems[] = { BUTTONPANEL, TEXTPANEL };
        JComboBox cb = new JComboBox(comboBoxItems);
        cb.setEditable(false);
        cb.addItemListener(this);
        comboBoxPane.add(cb);

        //Create the "cards".
        JPanel card1 = new JPanel();
        card1.add(new JButton("Button 1"));
        card1.add(new JButton("Button 2"));
        card1.add(new JButton("Button 3"));

        JPanel card2 = new JPanel();
        card2.add(new JTextField("TextField", 20));

        //Create the panel that contains the "cards".
        cards = new JPanel(new CardLayout());
        cards.add(card1, BUTTONPANEL);
        cards.add(card2, TEXTPANEL);

        pane.add(comboBoxPane, BorderLayout.PAGE_START);
        pane.add(cards, BorderLayout.CENTER);
    }

    public void itemStateChanged(ItemEvent evt) {
        CardLayout cl = (CardLayout)(cards.getLayout());
        cl.show(cards, (String)evt.getItem());
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event dispatch thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("CardLayoutDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        CardLayoutDemo demo = new CardLayoutDemo();
        demo.addComponentToPane(frame.getContentPane());

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

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

You can easily modify it to you fulfill your goal.