您创建了一个使用cardlayout和卡片的JPanel，但是没有添加任何内容，因此它当然不会显示自身，也不会显示卡片。解决方案：将此JPanel添加到您的GUI。
所以代替：
main.setContentPane(welcomePanel());
做：
main.setContentPane(cards);
问题编号2：
将字符串用作键的类型时，请使用字符串常量。请注意，您因此将一个JPanel添加到卡JPanel中：
cards.add(home, "Home");
但是，然后尝试像这样显示它：
cl.show(cards, "home");
但是“家”与“家”不同。
而是声明一个常量HOME：
public static final String HOME = "home";
举一个简单的例子：
import java.awt.cardlayout;
import java.awt.event.ActionEvent;
import javax.swing.*;
public class MainGui2 extends JPanel {
private cardlayout cardlayout = new cardlayout();
private WelcomePanel welcomePanel = new WelcomePanel(this);
private HomePanel homePanel = new HomePanel();
public MainGui2() {
setLayout(cardlayout);
add(welcomePanel, WelcomePanel.NAME);
add(homePanel, HomePanel.NAME);
}
public void showCard(String name) {
cardlayout.show(this, name);
}
private static void createAndShowGui() {
MainGui2 mainPanel = new MainGui2();
JFrame frame = new JFrame("MainGui2");
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();
}
});
}
}
class WelcomePanel extends JPanel {
public static final String NAME = "welcome panel";
private MainGui2 mainGui2;
public WelcomePanel(final MainGui2 mainGui2) {
this.mainGui2 = mainGui2;
add(new JLabel(NAME));
add(new JButton(new AbstractAction("logon") {
@Override
public void actionPerformed(ActionEvent e) {
mainGui2.showCard(HomePanel.NAME);
}
}));
}
}
class HomePanel extends JPanel {
public static final String NAME = "home panel";
public HomePanel() {
add(new JLabel(NAME));
}
}
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