CardLayout的问题

Question

我正在学习关于YouTube on CardLayout的教程。我下载了原码，结果很好。但是对于我想要做的程序，我需要一个单独的类来运行应用程序(即只使用main方法的单独的类)、JFrame的单独的类以及JPanel的至少一个单独的类。我试着分离代码，但它为我显示了一个空白的JFrame。

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

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

public class CardJPanel extends JPanel
{
    JPanel panelCont = new JPanel();
    JPanel panelFirst = new JPanel();
    JPanel panelSecond = new JPanel();
    JButton buttonOne = new JButton("Switch to second panel");
    JButton buttonSecond = new JButton("Switch to first panel");
    CardLayout cl = new CardLayout();

    public CardJPanel()
    {
        panelCont.setLayout(cl);

        panelFirst.add(buttonOne);
        panelSecond.add(buttonSecond);
        panelFirst.setBackground(Color.BLUE);
        panelSecond.setBackground(Color.GREEN);

        panelCont.add(panelFirst, "1");
        panelCont.add(panelSecond, "2");
        cl.show(panelCont, "1");

        buttonOne.addActionListener(new ActionListener()
        {
            @Override
            public void actionPerformed(ActionEvent arg0)
            {
                cl.show(panelCont, "2");
            }
        });

        buttonSecond.addActionListener(new ActionListener()
        {
            @Override
            public void actionPerformed(ActionEvent arg0)
            {
                cl.show(panelCont, "1");
            }
        });
    }
}

import javax.swing.JFrame;

public class Frame extends JFrame
{
    public Frame()
    {
        CardJPanel panel = new CardJPanel();
        setContentPane(panel);
        setVisible(true);

// if I do this it displays the panel just fine
        JPanel panel2 = new JPanel();
        panel.setBackground(Color.MAGENTA);
        setContentPane(panel2);
    }
}

import javax.swing.JFrame;

public class Main
{
    public static void main(String[] args)
    {
        Frame startFrame = new Frame();
        startFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        startFrame.setSize(450, 400);
        startFrame.setVisible(true);
    }

}

Answer 1

在CardJPanel中，您应该添加以下一行：

this.add(panelCont);

可能就在你展示它之前：

public CardJPanel()
{
    panelCont.setLayout(cl);
    this.add(panelCont);
    panelFirst.add(buttonOne);
    panelSecond.add(buttonSecond);
    panelFirst.setBackground(Color.BLUE);
    panelSecond.setBackground(Color.GREEN);

    panelCont.add(panelFirst, "1");
    panelCont.add(panelSecond, "2");

    this.add(panelCont);
    cl.show(panelCont, "1");

    buttonOne.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent arg0)
        {
            cl.show(panelCont, "2");
        }
    });

    buttonSecond.addActionListener(new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent arg0)
        {
            cl.show(panelCont, "1");
        }
    });

}

你有JPanel panelCont，但实际上它从未被使用过。您希望将其添加到JPanel (或CardJPanel)本身，以便显示它。