我试图在用户登录后在下一张卡上显示用户名，但没有运气。
我正在使用CardLayout并定义了两张卡片 - 一张卡片供用户输入名称＆amp;密码和第二个显示登录uner名称的欢迎消息。我正在学习Java＆amp;摇摆我自己而不是专家。任何帮助，包括修复此代码或参考资料供我阅读，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;
}
}
答案 0 :(得分：4)
您在代码中声明并初始化JPanel cards两次，一次作为实例变量，第二次在CardLayoutLoginTest类的构造函数内。
由于你的是一步一步的，所以你最好将JPanel作为Cards逐一添加到CardLayout。因为如果LoginFails你不需要它们，只要登录有效时添加你想要添加到CardLayout的内容。
请使用setLocationByPlatform(true);代替setLocationRelativeTo(null);。正如@Andrew Thompson在他的一篇文章How to best position Swing GUI's中所解释的那样，前者更好
我修改了你的代码，看看并告诉我它是否缺少什么。
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的小型示例程序：
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);
}
}
答案 1 :(得分：3)
每次CardLayout触发时都会重新创建JButton's Action个实例，只创建一次，例如
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class OnTheFlyImageTest extends JFrame {
private static final long serialVersionUID = 1L;
private JPanel cardPanel;
private CardLayout cardLayout;
public OnTheFlyImageTest() {
JPanel cp = new JPanel(new BorderLayout());
cp.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
cardLayout = new CardLayout(5, 5);
cardPanel = new JPanel(cardLayout);
cp.add(cardPanel);
for (int i = 0; i < 5; i++) {// Create random panels for testing.
String name = "ImagePanel" + (i + 1);
String image = (i & 1) == 0 ? "foo.gif" : "bar.gif";
Color clr = (i & 1) == 0 ? Color.red : Color.blue;
ImagePanel imgPanel = new ImagePanel(name, image, clr);
cardPanel.add(imgPanel, name);
cardLayout.addLayoutComponent(imgPanel, name);
}
JPanel buttonPanel = new JPanel(new GridLayout(1, 2, 5, 5));
JButton prevButton = new JButton("< Previous");
prevButton.setActionCommand("Previous");
prevButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
cardLayout.previous(cardPanel);
}
});
buttonPanel.add(prevButton);
JButton nextButton = new JButton("Next >");
nextButton.setActionCommand("Next");
nextButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
cardLayout.next(cardPanel);
}
});
buttonPanel.add(nextButton);
JPanel temp = new JPanel(new BorderLayout());
temp.add(buttonPanel, BorderLayout.LINE_END);
cp.add(temp, BorderLayout.SOUTH);
setContentPane(cp);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setTitle("Test");
pack();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new OnTheFlyImageTest().setVisible(true);
}
});
}
}
class ImagePanel extends JPanel {
private static final long serialVersionUID = 1L;
private String imgString;
private JLabel imgLabel;
public ImagePanel(String name, String imgString, Color backGround) {
setName(name);
this.imgString = imgString;
setLayout(new BorderLayout());
setBackground((backGround));
// Ensure size is correct even before any image is loaded.
setPreferredSize(new Dimension(400, 300));
}
@Override
public void setVisible(boolean visible) {
if (visible) {
System.err.println(getName() + ": Loading and adding image");
ImageIcon icon = new ImageIcon(imgString);
imgLabel = new JLabel(icon);
add(imgLabel);
}
super.setVisible(visible);
if (!visible) { // Do after super.setVisible() so image doesn't "disappear".
System.err.println(getName() + ": Removing image");
if (imgLabel != null) { // Before display, this will be null
remove(imgLabel);
imgLabel = null; // Hint to GC that component/image can be collected.
}
}
}
}