如何使用JComboBox更新Jpanel

我是java語言的新手，我正在嘗試創建一個具有JComboBox的GUI，以允許用戶選擇其中一個選項，并根據所選選項通過添加更多文本欄位來更新面板。目前我面臨一個問題，如果我選擇（選擇 1）面板不會更新，它應該出現 5 個帶有標簽的文本欄位。

我的問題是：如何根據用戶從 JComboBox 中選擇的選項更新面板以添加更多文本欄位？

另外，我面臨另一個問題，我找不到設定 JFrame 大小的方法

這是我的代碼：

import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.border.EmptyBorder;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class RTSS extends JFrame implements ActionListener {

private JComboBox cb;
JPanel main;
JPanel panel3;
JPanel panel2;
JPanel panel1;
GridBagConstraints gbc;
String[] choices;
JLabel Label1;
JLabel Label2;
JLabel Label3;
JLabel Label4;
JLabel Label5;
JTextField tf1;
JTextField tf2;
JTextField tf3;
JTextField tf4;
JTextField tf5;



public RTSS() {
    Border blackline = BorderFactory.createLineBorder(Color.black);
    EmptyBorder b1 = new EmptyBorder(5, 0, 0, 0);
    main = new JPanel(new FlowLayout(FlowLayout.LEFT));

    panel3 = new JPanel(new FlowLayout(FlowLayout.LEFT));
    panel3.setAlignmentX(1);
    panel3.setPreferredSize(new Dimension(800, 35));
    panel3.setBorder(b1);
    main.add(panel3);

    panel2 = new JPanel();
    panel1 = new JPanel();
    panel1.setPreferredSize(new Dimension(700, 500));
    panel1.setBorder(blackline);
    panel1.setLayout(new GridBagLayout());
    gbc = new GridBagConstraints();
    choices = new String[]{ "","Choice 1", "Choice 2", "Choice 3 "};
    cb = new JComboBox(choices);

    //Main inputs (labels)
    Label1 = new JLabel("Label 1 ");
    Label2 = new JLabel("Label 2 ");
    Label3 = new JLabel("Label 3");
    Label4 = new JLabel("Label 4 ");
    Label5 = new JLabel("Label 5 ");

    //TextFields
    tf1 = new JTextField(10);
    tf2 = new JTextField(10);
    tf3 = new JTextField(10);
    tf4 = new JTextField(10);
    tf5 = new JTextField(10);
    gbc.anchor = GridBagConstraints.NORTHWEST;
    gbc.weightx = 0;
    gbc.weighty = 0;
    gbc.insets = new Insets(10, 3, 5, 0);
    panel3.add(cb);
    panel2.add(panel1);
    gbc.gridx = 0;
    gbc.gridy = 0;
    panel1.add(Label1, gbc);
    gbc.gridx = 0;
    gbc.gridy = 1;
    panel1.add(Label2, gbc);
    gbc.gridx = 0;
    gbc.gridy = 2;
    panel1.add(Label3, gbc);
    gbc.gridx = 1;
    gbc.gridy = 0;
    panel1.add(tf1, gbc);
    gbc.gridx = 1;
    gbc.gridy = 1;
    panel1.add(tf2, gbc);
    gbc.weightx = 0.5;
    gbc.weighty = 0.5;
    gbc.gridx = 1;
    gbc.gridy = 2;
    panel1.add(tf3, gbc);
    main.add(panel2);
    add(main);


}
@Override
public void actionPerformed(ActionEvent e) {
    String Choice = cb.getSelectedItem().toString();
    if ("Choice 1".equals(Choice)) {
        gbc.gridx = 0;
        gbc.gridy = 3;
        panel1.add(Label4, gbc);
        gbc.gridx = 1;
        gbc.gridy = 3;
        panel1.add(tf4, gbc);
        gbc.gridx = 0;
        gbc.gridy = 4;
        panel1.add(Label5, gbc);
        gbc.weightx = 6;
        gbc.weighty = 1;
        gbc.gridx = 1;
        gbc.gridy = 4;
        panel1.add(tf5, gbc);
    }
}

public static void main(String[] args) {

    try {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
    } catch (Exception ex) {
        ex.printStackTrace();
    }

    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            new RTSS().setVisible(true);
        }
    });
}
}

uj5u.com熱心網友回復：

將以下行添加到 RTSS 建構式的末尾：

public RTSS() {
    //your code

    //this lines 
    pack();        
    setLocationRelativeTo(null);
    cb.addActionListener(this);
}

這 3 行將 1.設定布局，2.居中框架和 3.激活 ActionListener。如果您現在在 ComboBox 中進行選擇，您的代碼將在 ActionListener 中執行。

在 ComboBox 中選擇更改布局后，再次呼叫 pack()。

@Override
public void actionPerformed(ActionEvent e) {
    String Choice = cb.getSelectedItem().toString();
    if ("Choice 1".equals(Choice)) {
         // your code

        pack();
    }
}

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