Swing 在JButton Actionlistener中重置JTextfield

我正在使用CardLayout开发一个预算应用程序。下面的代码创建了一个JPanel主面板，其中包含一个名为homePageCard的主页JPanel卡和另一个名为addItemCard的JPanel卡。当我单击名为Add Item的JButton AddItem按钮时，它会成功地将我带到addItemCard

我还插入了一个名为previous to my addItemCard的按钮，将我带回homePageCard，为用户添加了一个saveBudgetItem按钮以保存其预算项目数据，并在addItemCard中添加了两个JTextFields：budget_item_Title_字段和budget_Amount_字段。如果用户试图通过单击JButton saveBudgetItemButton来保存预算项目，而不填写这两个文本字段中的任何一个，或者如果这两个字段中的任何一个包含空字符串，则用户应收到一个JOptionPane错误消息对话框。如果保存成功，另一个JOptionPane对话框应告诉用户预算项目已成功保存

问题的症结在于：当我点击previous进入homepageCard并清除previous按钮的操作侦听器中的文本字段，然后按Add Item按钮返回addItemCard时，它通过使用budget_Item_Title_Field.setText和budget_Amount_Field.setText成功地清除了这两个文本字段

但是，当我为两个文本字段键入新文本并单击saveBudgetItem JButton时，我错误地得到下面详细说明的错误消息，即JOptionPane.showmessagedialog消息，并抱怨当两个字段都不为空时，两个文本字段中仍有空字符串

如何使我在单击“上一步”按钮并在各自的文本字段中键入新预算项目的标题和金额后返回addItemCard时，程序识别更新的文本字段不再包含空字符串

这是我的主要课程代码：

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

public class Main
{
    public static void main(String[] args)
    { 
        SwingUtilities.invokeLater(new Runnable() {
        public void run() {
           // Create main GUI to display and to use software, and add contents to it
           HomePage h = new HomePage();
        }});
    }
}

这是我的主页类代码：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

public class HomePage extends JFrame {
    // Panel to contain contents of JFrame
    private static JPanel contentPanel = new JPanel(new BorderLayout());
    private static Dimension screenDimensions = Toolkit.getDefaultToolkit().getScreenSize();
    private static int screenWidth = screenDimensions.width;
    private static int screenHeight = screenDimensions.height;
    private static int frameWidth = 800;
    private static int frameHeight = 510;

    // the following are components for card layout and widgets for entering budget data
    private static JPanel main_panel = new JPanel(new CardLayout());
    private static JPanel homeCard = new JPanel(new BorderLayout());
    private static JPanel addItemCard = new JPanel(new BorderLayout());
    private static JPanel textfieldPanel = new JPanel(new FlowLayout());
    private static JTextField budget_Title_Field;
    private static JTextField amount_Field;
    private static JButton previous = new JButton("<< previous");
    private static JButton addItemButton = new JButton("Add Revenue or Expense");
    private static JButton saveBudgetItemButton = new JButton("Save Budget Item");

    public HomePage() {
        // format frame
        setSize(frameWidth, frameHeight);
        setResizable(false);
        setLocation((screenWidth - frameWidth) / 2, (screenHeight - frameHeight) / 2);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        // format home page and add all cards to main_panel to manipulate them in card layout       
        formatHomeCard(homeCard);

        // add all cards to main_panel
        main_panel.add(homeCard, "Home");
        main_panel.add(addItemCard, "Add Item");

       // add main_panel to home JFrame
       this.add(main_panel);
    }

    public static void formatHomeCard(JPanel homeCard)
    {
        // Add functionality to addItemButton so it switches the card to the Add Item page
        addItemButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                // Adds all of the contents of the add revenue or expense page to the           
                // addItemCard
                formatAddItemCard(addItemCard);

                // If the add item button is pressed, switch the JPanel so that the add item card  
                // shows
                CardLayout cardLayout = (CardLayout) main_panel.getLayout();
                cardLayout.show(main_panel, "Add Item");
           }
        });

        // Add the addItemButton to the home page
        homeCard.add(addItemButton, BorderLayout.CENTER);
    }

    // the purpose of this method is to add all contents to addItemCard
    public static void formatAddItemCard(JPanel addItemCard)
    {
        // add 2 jtextfields, one for the budget title and the other for the budget amount
        // I excluded irrelevant JLabels, etc. for the sake of avoiding unnecessary details
        textfieldPanel.add(budget_Title_Field);
        textfieldPanel.add(amount_Field);
        addItemCard.add(textfieldPanel, BorderLayout.NORTH);

       // add functionality to save budget item button and add it to addItemCard
       saveBudgetItemButton.addActionListener(new ActionListener()
       {
             public void actionPerformed(ActionEvent e)
             {
                // If the data fields are complete, create and serialize the budget item. Else,
                // prompt the user for more information.   
                if (!(budget_Title_Field.getText().equals("")) && !(amount_Field.getText().equals("")))
                 {
                     // will save the budget data here. confirm the user saved the budget item.
                     JOptionPane.showMessageDialog(null, "Success! Your budget item was saved and has been integrated into your budget.");
                 }

                 // if either budget item title or amount is missing, complain and don't save budget item
                if (budget_Title_Field.getText().equals("") || amount_Field.getText().equals(""))
                {
                    // PROBLEMATIC CODE HERE: INCORRECTLY ASSUMES TEXTFIELDS ARE EMPTY WHEN THEY'RE 
                    // NOT AFTER CLICKING ON "PREVIOUS" BUTTON, THEN RETURNING TO THIS PAGE BY 
                    // CLICKING "ADD REVENUE OR EXPENSE" BUTTON
                    // print out error message that budget item title and amount is incomplete
                    JOptionPane.showMessageDialog(null, "Please enter in both the budget item title and dollar amount to continue.");
                }
            }
       });

       addItemCard.add(saveBudgetItemButton, BorderLayout.CENTER);

       // Add functionality to previous button and add it to the addItemCard
       previous.addActionListener(new ActionListener()
       {
            public void actionPerformed(ActionEvent e)
            {   
                // If the previous button is pressed, switch the JPanel so that the home page card shows
                CardLayout cardLayout = (CardLayout) main_panel.getLayout();
                cardLayout.show(main_panel, "Home");

                budget_Title_Field.setText("");
                amount_Field.setText("");
                isExpenseButton.setSelected(true); 
            }
        });

        addItemCard.add(previous, BorderLayout.SOUTH);
    }
}

---

如果我进行修改以使示例程序运行，它将按预期工作。您是否可能在真实代码中的某个地方创建新的文本字段，以便检查错误的字段？我在类的顶端初始化了它们，而不是在其他地方。