java - 如何在 CardLayout Swap 上将一张卡片的文本字段值显示到另一张卡片

Question

我试图在用户登录后在下一张卡片上显示用户名，但没有成功。

我正在使用 CardLayout 并定义了两张卡片 - 一张用于用户输入名称和密码的卡片，第二张用于显示带有已登录用户名的欢迎消息。我自己学习 Java 和 Swing，而不是专家。任何帮助，包括修复此代码或供我阅读的引用，都将不胜感激。

这是我当前的代码(仍然需要添加代码来更新欢迎屏幕的文本字段):

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

public class CardTest
{   
    private JFrame frame;
    public static final String CARD_LOGIN =  "Card Login"; 
    public static final String CARD_DEPARTMENT = "Card Department";
    public static final String CARD_TEAM = "Card Team";
    public static JPanel cards;
    public Employee employee = null;
    public CardLogin cardLogin = null;
    public CardDepartment cardDepartment = null;
    public CardTeam cardTeam = null;

    public CardTest()
    {
        Employee employee = new Employee();

        frame = new JFrame("Card Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(true);

        cards = new JPanel();
        cards.setLayout(new CardLayout(20, 20));

        cardLogin = new CardLogin(this, employee);
        cardDepartment = new CardDepartment(this, employee);
        cardTeam = new CardTeam(this, employee);

        cards.add(cardLogin, CARD_LOGIN);       
        cards.add(cardDepartment, CARD_DEPARTMENT);
        cards.add(cardTeam, CARD_TEAM);

        frame.getContentPane().add(cards);
        frame.pack();
        frame.setVisible(true);
    }

    public void swapView(String key) 
    {
        CardLayout cardLayout = (CardLayout) cards.getLayout();
        cardLayout.show(cards, key);
    }

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

class CardLogin extends JPanel 
{ 
    private ActionListener action; 
    private JTextField tfUsername= null; 
    Employee employee;
    CardTest cardTest;

    public CardLogin(CardTest cardTest, Employee employee) 
    { 
        this.cardTest = cardTest;
        this.employee = employee;
        init(); 
    } 

    private void init() 
    { 
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();

        gc.fill = GridBagConstraints.HORIZONTAL;

        JLabel lbCardName = new JLabel("Login Card ");
        gc.gridx = 1;
        gc.gridy = 0;
        gc.gridwidth = 2;
        panel.add(lbCardName, gc);

        JLabel lbUsername = new JLabel("Username: ");
        gc.gridx = 0;
        gc.gridy = 2;
        gc.gridwidth = 1;
        panel.add(lbUsername, gc);

        tfUsername = new JTextField(20);
        gc.gridx = 1;
        gc.gridy = 2;
        gc.gridwidth = 2;
        panel.add(tfUsername, gc);

        JLabel lbPassword = new JLabel("Password: ");
        gc.gridx = 0;
        gc.gridy = 3;
        gc.gridwidth = 1;
        panel.add(lbPassword, gc);

        JPasswordField pfPassword = new JPasswordField(20);
        gc.gridx = 1;
        gc.gridy = 3;
        gc.gridwidth = 2;
        panel.add(pfPassword, gc);

        final JButton loginButton = new JButton("Login"); 

        action = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {
                if (tfUsername.getDocument().getLength() > 0)   
                {
                    employee.setUserName(tfUsername.getText());
                    cardTest.swapView(cardTest.CARD_DEPARTMENT);
                }
            } 
        }; 

        loginButton.addActionListener(action); 

        JPanel bp = new JPanel();
        bp.add(loginButton);

        setSize( 640, 480);

        add(panel, BorderLayout.CENTER);
        add(bp, BorderLayout.PAGE_END);
    } 
} 

class CardDepartment extends JPanel 
{ 
    private ActionListener actionNext; 
    private ActionListener actionLogout; 
    private JTextField tfDepartment= null; 
    private String department= null;
    Employee employee;
    CardTest cardTest;
    CardLogin cardLogin;

    public CardDepartment(CardTest cardTest, Employee employee) 
    { 
        this.employee = employee;
        this.cardTest = cardTest;
        init(); 
    } 

    private void init() 
    { 
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();
        gc.fill = GridBagConstraints.HORIZONTAL;

        JLabel lbCardName = new JLabel("Department Card ");
        gc.gridx = 1;
        gc.gridy = 0;
        gc.gridwidth = 2;
        panel.add(lbCardName, gc);

        JLabel lbWelcome = new JLabel("Welcome ");
        gc.gridx = 0;
        gc.gridy = 2;
        gc.gridwidth = 1;
        panel.add(lbWelcome, gc);

        gc.gridx = 1;
        gc.gridy = 2;
        gc.gridwidth = 2;
        panel.add(new JLabel(employee.getUserName()), gc);

        JLabel lbDepartment = new JLabel("Enter Department: ");
        gc.gridx = 0;
        gc.gridy = 3;
        gc.gridwidth = 1;
        panel.add(lbDepartment, gc);

        tfDepartment = new JTextField(20);
        gc.gridx = 1;
        gc.gridy = 3;
        gc.gridwidth = 2;
        panel.add(tfDepartment, gc);

        final JButton nextButton = new JButton("Next"); 
        actionNext = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {
                if (tfDepartment.getDocument().getLength() > 0)   
                {
                    department = tfDepartment.getText();
                    cardTest.swapView(cardTest.CARD_TEAM);
                }
            } 
        }; 

        final JButton logoutButton = new JButton("Logout"); 
        actionLogout = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {
                    cardTest.swapView(cardTest.CARD_LOGIN);
            } 
        }; 

        nextButton.addActionListener(actionNext); 
        logoutButton.addActionListener(actionLogout); 

        JPanel bp = new JPanel();
        bp.add(panel);
        bp.add(logoutButton);
        bp.add(nextButton);

        add(panel);
        add(bp); 
    } 
}

class CardTeam extends JPanel 
{ 
    private ActionListener actionPrev; 
    private ActionListener actionLogout; 
    private JTextField tfTeam= null; 
    Employee employee;
    CardTest cardTest;

    public CardTeam(CardTest cardTest, Employee employee) 
    { 
        this.cardTest = cardTest;
        this.employee = employee;
        init(); 
    } 

    private void init() 
    { 
        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();
        gc.fill = GridBagConstraints.HORIZONTAL;

        JLabel lbCardName = new JLabel("Team Card ");
        gc.gridx = 1;
        gc.gridy = 0;
        gc.gridwidth = 2;
        panel.add(lbCardName, gc);

        JLabel lbWelcome = new JLabel("Welcome ");
        gc.gridx = 0;
        gc.gridy = 2;
        gc.gridwidth = 1;
        panel.add(lbWelcome, gc);

        gc.gridx = 1;
        gc.gridy = 2;
        gc.gridwidth = 2;
        panel.add(new JLabel(employee.getUserName()), gc);

        JLabel lbDepartment = new JLabel("Department: ");
        gc.gridx = 0;
        gc.gridy = 3;
        gc.gridwidth = 1;
        panel.add(lbDepartment, gc);

        gc.gridx = 1;
        gc.gridy = 3;
        gc.gridwidth = 2;
        panel.add(new JLabel(employee.getDepartment()), gc);

        JLabel lbTeam = new JLabel("Enter Team: ");
        gc.gridx = 0;
        gc.gridy = 4;
        gc.gridwidth = 1;
        panel.add(lbTeam, gc);

        tfTeam = new JTextField(20);
        gc.gridx = 1;
        gc.gridy = 4;
        gc.gridwidth = 2;
        panel.add(tfTeam, gc);

        final JButton prevButton = new JButton("Prev"); 
        actionPrev = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {
                    cardTest.swapView(cardTest.CARD_DEPARTMENT);
            } 
        }; 

        final JButton logoutButton = new JButton("Logout"); 
        actionLogout = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {
                    cardTest.swapView(cardTest.CARD_LOGIN);
            } 
        }; 

        prevButton.addActionListener(actionPrev); 
        logoutButton.addActionListener(actionLogout); 

        JPanel bp = new JPanel();
        bp.add(logoutButton);
        bp.add(prevButton);

        add(panel);
        add(bp); 
    } 
}

class Employee
{ 
    private String userName = null;
    private String department = null;
    private String team = null;

    public Employee() {
        super();
    }

    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    public String getDepartment() {
        return department;
    }
    public void setDepartment(String department) {
        this.department = department;
    }
    public String getTeam() {
        return team;
    }
    public void setTeam(String team) {
        this.team = team;
    }
}

Answer 1

您在代码中两次声明和初始化JPanel 卡片，一次作为实例变量，第二次在CardLayoutLoginTest 类的构造函数中。因为你的是一步一步的事情，所以你最好将你的 JPanel 添加到 CardLayout 中，一个一个地充当 Cards。因为如果 LoginFails 您将不需要它们，只需在登录有效时将您想要添加的内容添加到 CardLayout。

请使用 setLocationByPlatform(true);而不是 setLocationRelativeTo(null);。正如@Andrew Thompson 在他的一篇帖子中所解释的那样，前者更好，How to best position Swing GUI's我已经修改了您的代码，请查看并告诉我是否缺少某些内容。

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

public class CardTest
{   
    private JFrame frame;
    public static final String CARD_LOGIN =  "Card Login"; 
    public static final String CARD_WELCOME = "Card Welcome";
    public static JPanel cards;
    public CardLogin cardLogin = null;

    public CardTest()
    {
        frame = new JFrame("Card LOGIN");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(true);

        cards = new JPanel();
        cards.setLayout(new CardLayout(20, 20));

        cardLogin = new CardLogin(this);
        cards.add(cardLogin, CARD_LOGIN);       

        frame.getContentPane().add(cards);
        frame.pack();
        frame.setVisible(true);
    }

    public void swapView(String key) 
    {
        CardLayout cardLayout = (CardLayout) cards.getLayout();
        cardLayout.show(cards, key);
    }

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

class CardLogin extends JPanel 
{ 
    private ActionListener action; 
    CardTest cardLayoutLoginTest;
    /*
     *  Made JTextField an instance variable so that
     * ActionListener can access it or you can make 
     * it final.
     */
    private JTextField tfUsername= null; 
    private String username = null;

    public CardLogin(CardTest cardLayoutLoginTest) 
    { 
        this.cardLayoutLoginTest = cardLayoutLoginTest;
        init(); 
    } 

    private void init() 
    { 

        JPanel panel = new JPanel(new GridBagLayout());
        GridBagConstraints gc = new GridBagConstraints();

        gc.fill = GridBagConstraints.HORIZONTAL;

        JLabel lbUsername = new JLabel("Username: ");
        gc.gridx = 0;
        gc.gridy = 0;
        gc.gridwidth = 1;
        panel.add(lbUsername, gc);

        tfUsername = new JTextField(20);
        gc.gridx = 1;
        gc.gridy = 0;
        gc.gridwidth = 2;
        panel.add(tfUsername, gc);

        JLabel lbPassword = new JLabel("Password: ");
        gc.gridx = 0;
        gc.gridy = 1;
        gc.gridwidth = 1;
        panel.add(lbPassword, gc);

        JPasswordField pfPassword = new JPasswordField(20);
        gc.gridx = 1;
        gc.gridy = 1;
        gc.gridwidth = 2;
        panel.add(pfPassword, gc);

        final JButton loginButton = new JButton("Login"); 

        action = new ActionListener() 
        { 
            public void actionPerformed(ActionEvent ae) 
            {

                    // Here need code to update text filed of welcome card
                /*
                 * Here we are first checking if there is any text inside
                 * the JTextField for USERNAME, if found we will send it to the
                 * next JPanel which will be serving as a new Card.
                 */ 
                if (tfUsername.getDocument().getLength() > 0)   
                {
                    username = tfUsername.getText();
                    CardWelcome cardWelcome = new CardWelcome(cardLayoutLoginTest.cardLogin);
                    CardTest.cards.add(cardWelcome, cardLayoutLoginTest.CARD_WELCOME);
                    cardLayoutLoginTest.swapView(cardLayoutLoginTest.CARD_WELCOME);
                }
            } 
        }; 

        loginButton.addActionListener(action); 

        JPanel bp = new JPanel();
        bp.add(loginButton);

        /*set size of the frame*/
        setSize( 640, 480);

        add(panel, BorderLayout.CENTER);
        add(bp, BorderLayout.PAGE_END);

    } 

    public String getUserName()
    {
        return username;
    }
} 

class CardWelcome extends JPanel 
{ 
    private JTextField textField;
    private CardLogin cardLogin;

    public CardWelcome(CardLogin cl) 
    { 
        cardLogin = cl;
        init(); 
    } 

    private void init() 
    { 
        setLayout(new GridLayout(1, 1)); 
        JLabel userLabel = new JLabel("Welcome "); 
        textField = new JTextField(); 
        textField.setText(cardLogin.getUserName());
        System.out.println("UserName : " + cardLogin.getUserName());

        add(userLabel); 
        add(textField); 
    } 
}

在运行时更新 JLabel 的小示例程序:

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

public class UpdateLabel extends JFrame
{
    private int count = 0;
    public UpdateLabel()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationByPlatform(true);

        final JPanel contentPane = new JPanel();
        contentPane.setLayout(new BorderLayout());

        final JLabel label = new JLabel("JLabel " + count);
        JButton button = new JButton("UPDATE JLABEL");
        button.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {
                count++;
                label.setText("JLabel " + count);
                contentPane.revalidate(); // sometimes you require to do this and the below line.
                contentPane.repaint();
            }
        });

        contentPane.add(label, BorderLayout.CENTER);
        contentPane.add(button, BorderLayout.PAGE_END);

        setContentPane(contentPane);
        pack();
        setVisible(true);
    }

    public static void main(String... args)
    {
        Runnable runnable = new Runnable()
        {
            public void run()
            {
                new UpdateLabel();
            }
        };
        SwingUtilities.invokeLater(runnable);
    }
}