JButton无法显示JPanel

Question

I want to call My JPanel with button. My Jpanel is actually a sub JPanel from main Panel with card layout.

to do that, i am using card layout api method HERE to show the JPanel after a button was clicked.

JButton btnCallPanel1 = new JButton("Call PanelOne");
   btnCallPanel1.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {

            CardLayout card = (CardLayout)mainPanel.getLayout();
            card.show(mainPanel, "PanelOne");                     //call Panel One

        }  

output :

nothing appear, panel not called and no error pop out.

My Code is HERE

package wan.dev.sample.cardlayout;

import java.awt.CardLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

import javax.swing.JLabel;

public class HowToUseCardLayout {

    private JFrame frame;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    HowToUseCardLayout window = new HowToUseCardLayout();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public HowToUseCardLayout() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 688, 358);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JPanel mainPanel = new JPanel();
        mainPanel.setBounds(0, 0, 672, 260);
        frame.getContentPane().add(mainPanel);
        mainPanel.setLayout(new CardLayout(0, 0));

                JPanel PrePanel = new JPanel();
                mainPanel.add(PrePanel, "name_246268073832057");
                PrePanel.setLayout(null);

                        JLabel lblPanel_1 = new JLabel("Pre Panel");
                        lblPanel_1.setBounds(280, 115, 57, 20);
                        PrePanel.add(lblPanel_1);

        JPanel panelOne = new JPanel();
        mainPanel.add(panelOne, "name_246268067657434");
        panelOne.setLayout(null);

        JLabel lblPanel = new JLabel("panel 1");
        lblPanel.setBounds(279, 118, 46, 14);
        panelOne.add(lblPanel);

        JButton btnPan1 = new JButton("Call PanelOne");
        btnPan1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                CardLayout card = (CardLayout) mainPanel.getLayout();
                card.show(mainPanel, "PanelOne");

            }
        });
        btnPan1.setBounds(262, 286, 144, 23);
        frame.getContentPane().add(btnPan1);
    }
}

ANSWER

The reason i cant call my panel because i did not call it by using identifier. i have to give identifier name to my desire jpanel and use the identifier on my cardLayout.show(..)

Public Static final String PANEL_ONE = "panel one";                  //Name of JPanel Identifier


//add panel to main panel and declare panelOne identifier
mainPanel.add(panelOne, PANEL_ONE);                         //PANEL_ONE function like 
                                                            //an identifier


JButton btnCallPanel1 = new JButton("Call PanelOne");
btnCallPanel1.addActionListener(new ActionListener() {
  public void actionPerformed(ActionEvent e) {

        CardLayout card = 
                     (CardLayout)mainPanel.getLayout();

        card.show(mainPanel, PANEL_ONE);                     //call panelOne using PANEL_ONE 
                                                             //instead of JPanel name

    }  

Answer 1

As I suspected — You're calling the CardLayout.show(...) method with the String parameter "PanelOne", but yet you've not added any component to the CardLayout-using container using this same String, so it makes sense that it won't work. Solution: don't do this. Use the Same String that you add the component to the CardLayout using container as the one that you use to display it.

ie, If you want to display container foo and use the String "bar" to add it to the CardLayout -using container, then you must pass "bar" into the CardLayout 's show(...) method. Again, use String constants for this so that you reduce the chances of messing up.

Other issues: You're using null layout and setBounds — Don't. Doing this makes for very inflexible GUI's that while they might look good on one platform look terrible on most other platforms or screen resolutions and that are very difficult to update and maintain.

eg,

import java.awt.CardLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class CardLayoutFoo extends JPanel {
   public static final String BAR = "bar";
   public static final String BUTTON_PANEL = "button panel";
   private CardLayout cardlayout = new CardLayout();

   public CardLayoutFoo() {
      setLayout(cardlayout);

      JLabel fooLabel = new JLabel("Foo", SwingConstants.CENTER);
      add(fooLabel, BAR); // added using String constant, BAR

      JButton showFooBtn = new JButton(new AbstractAction("Show Foo") {

         @Override
         public void actionPerformed(ActionEvent evt) {
            // use same String, BAR, to get the fooLabl shown
            cardlayout.show(CardLayoutFoo.this, BAR);
         }
      });
      JPanel btnPanel = new JPanel();
      btnPanel.add(showFooBtn);
      add(btnPanel, BUTTON_PANEL);

      cardlayout.show(this, BUTTON_PANEL);            
   }

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

      JFrame frame = new JFrame("CardLayoutFoo");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_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();
         }
      });
   }
}