我正在使用 CardLayout 编写一个简单的程序。主屏幕应显示一个按钮，按下该按钮将转到下一个屏幕，该屏幕包含另一个屏幕的另一个按钮。我的问题是，当我运行我的程序时，屏幕是黑色的。我尝试按照在线教程编写自己的程序，但我似乎没有发现我的代码有问题。运行时我没有收到任何错误。这是我的代码
//using CardLayout to change screen when action is performed
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.Popup;
import javax.swing.JOptionPane;
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.FlowLayout;
public class CL extends JFrame {
JPanel cardPanel;
JPanel cardPanelA;
JPanel cardPanelB;//to set different screens
CardLayout cl;
private JButton button1;
private JButton button2;
private JButton change;
private JLabel label;
private JTextField textField1;
private JTextField textField2;
JButton button;
public CL() {
super("This is a sample");
cardPanel = new JPanel();
cardPanelA = new JPanel();
cardPanelB = new JPanel();
cl = new CardLayout();
cardPanel.setLayout(cl);
button1 = new JButton("button1");
button2 = new JButton("button2");
change = new JButton("change screen");
label = new JLabel("this is a label");
textField1 = new JTextField(10);
textField2 = new JTextField("enter text", 6);
cardPanelA.add(change);
cardPanelA.add(label);
cardPanelA.add(textField1);
cardPanelA.add(textField2);
cardPanelB.add(button1);
cardPanelB.add(button2);
cardPanel.add(cardPanelA);
cardPanel.add(cardPanelB);
JPanel panel1 = new JPanel();
button = new JButton("initial button");
panel1.add(button);
theHandler handler = new theHandler();//make action listener
change.addActionListener(handler);
button1.addActionListener(handler);
button2.addActionListener(handler);
button.addActionListener(handler);
/*
getContentPane().add(panel1, BorderLayout.NORTH);
getContentPane().add(cardPanelA, BorderLayout.NORTH);
getContentPane().add(cardPanelB, BorderLayout.NORTH);
*/
}
private class theHandler implements ActionListener {
public void actionPerformed(ActionEvent event) {
if (event.getSource() == button) {
cl.show(cardPanel, "Panel A");
}
if (event.getSource() == change) {
cl.show(cardPanelB, "panelB");
}
if (event.getSource() == button2) {
cl.show(cardPanel, "PanelA");
}
if (event.getSource() == button1) {
JOptionPane.showMessageDialog(null, "this is the second screen");
}
}
}
}
/* 使用 CardLayout 的方法：创建一个 CardLayout 管理器并创建一堆不同的 JPanel * 每个都是不同的屏幕。制作一个将 CardLayout 存储为布局的面板。* 将不同的元素添加到每个面板（按钮、文本字段），然后将面板添加到存储 * CardLayout */ 的 JPanel
import javax.swing.JFrame;
public class CardTest {
public static void main(String[] args) {
CL object = new CL();
object.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
object.setSize(400, 400);
object.setVisible(true);
}
}
这可能很简单，但我不确定它是什么。一些建议将不胜感激。