JTextField 的 setText 方法不更新 JTextField 实例

Question

The below is part of code of a multi file project. I am posting only this code since I am unclear why setText method is not working. Not all code for this project is included.

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

        @SuppressWarnings("serial")

        public class Controller extends JFrame implements ActionListener,ListSelectionListener 
        {

            private JButton addButton;
            private JButton deleteButton;
            private JButton viewDetailsButton;
            private JPanel btnsPnl = new JPanel();
            private JPanel mainPnl = new JPanel();
            private JPanel dataPnl = new JPanel();
            private JPanel listPnl = new JPanel();
            private JLabel loanIdLabel = new JLabel("LoanId");
            private JLabel loanName = new JLabel("Loan Name");
            private JLabel loanLender = new JLabel("Lender");
            private JLabel loanAmount = new JLabel("Loan Amount");
            private JTextField loanIdFld = new JTextField(15);
            private JTextField loanNameFld = new JTextField(15);
            private JTextField lenderFld = new JTextField(15);
            private JTextField loanamountFld = new JTextField(15);
            private DefaultListModel dlm = new DefaultListModel();
            private JList jlst=new JList(dlm);

            private loansModel model;
            private loansView loansView;

            private int selectedListIndex;
            private ListSelectionModel listSelectionModel;


        public loansController(loansModel mo)
        {
           addButton = new JButton("Add Loan");
           deleteButton = new JButton("Delete Loan");
           viewDetailsButton = new JButton("View Details of all Loans");
           model = mo;
           loansView = new loansView(mo);   
        }

        /* Builds GUI for the controller component of the
         *  Model-View-Controller implementation
         */
        public void buildGUI()
        {
            GridBagLayout gbl = new GridBagLayout();
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx=0;
            gbc.gridy=0;
            dataPnl.setLayout(new GridLayout(4,2));
            dataPnl.add(loanIdLabel);
            dataPnl.add(loanIdFld);
            dataPnl.add(loanName);
            dataPnl.add(lenderFld);
            dataPnl.add(authorLabel);
            dataPnl.add(authorFld);
            dataPnl.add(priceLabel);
            dataPnl.add(loanamountFld); 
            gbl.setConstraints(dataPnl, gbc);
            mainPnl.add(dataPnl);    
            Dimension listDim = new Dimension(50,90);
            jlst.setPreferredSize(listDim);
            gbc.gridx = 0;
            gbc.gridy = 1;
            gbl.setConstraints(listPnl,gbc);
            listPnl.add(jlst);
            listSelectionModel= jlst.getSelectionModel();
            listSelectionModel.addListSelectionListener(new loansController(model));
            gbc.gridx=1;
            gbc.gridy=1;
            gbc.gridwidth=2;
            gbl.setConstraints(btnsPnl,gbc);    
            addButton.addActionListener(this);
            deleteButton.addActionListener(this);
            viewDetailsButton.addActionListener(this);
            btnsPnl.add(addButton);
            btnsPnl.add(deleteButton);
            btnsPnl.add(viewDetailsButton);
            mainPnl.add(listPnl);
            mainPnl.add(btnsPnl);
            getContentPane().add(mainPnl);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            setSize(800,400);
            setVisible(true);
        }

        /* Handles events coming from add,delete, and view Details 
         * buttons */
        public void actionPerformed(ActionEvent ae)
        {

            if (ae.getSource()==addButton)
            {
                String bId = loanIdFld.getText();
                String titFld = lenderFld.getText();
                String authFld = authorFld.getText();
                String priFld = loanamountFld.getText();
                boolean isAnumber;
                isAnumber = isNumeric(priFld);

                if (!isAnumber)
                {
                    JOptionPane.showMessageDialog(null, 
                        "Enter the correct loan amount",
                        "Error: Price entry",
                         JOptionPane.INFORMATION_MESSAGE);
                    priFld = loanamountFld.getText();
                    isAnumber = isNumeric(priFld);

                }

                else
                {           
                    Loan loanItem;
                    loanItem = new Loan(bId, titFld,
                    authFld,Double.parseDouble(priFld));
                    model.addLoan(loanItem);
                    dlm.addElement(bId);
                    setClearTextFld();
                }
            }

            else if (ae.getSource()== deleteButton)
            {
                model.deleteLoan(model.getSelectedListIndex());
                dlm.removeElementAt(model.getSelectedListIndex());
                setClearTextFld();
            } 

            else if (ae.getSource()==viewDetailsButton)
            {   
                loansView.buildGUI();

            }

        }




         /* This method clears the text field after the action Performed
          * method for the add and delete Buttons
          */
          public void setClearTextFld()
          {
               loanIdFld.setText("");
               lenderFld.setText("");
               authorFld.setText("");
               loanamountFld.setText("");
          }





          /* This value changed method gets the selected item in the JList
           * for performing the  
           */
          public void valueChanged(ListSelectionEvent e) 
          {

            listSelectionModel = (ListSelectionModel)e.getSource();

            int maxselectedListIndex = listSelectionModel.getMaxSelectionIndex();
            int minselectedListIndex = listSelectionModel.getMinSelectionIndex();

            System.out.println(selectedListIndex);  

            if (!listSelectionModel.isSelectionEmpty())
            {   
            for (int i = minselectedListIndex; i <= maxselectedListIndex; i++) {
                if (listSelectionModel.isSelectedIndex(i)) 
                {  
                   selectedListIndex=i;
                   System.out.println("inside valueChanged. selectedListIndex");
                   System.out.println(selectedListIndex);
                   model.setSelectedListIndex(i);
                   Loan selectedLoan = model.getLoan(i);
                   System.out.println(selectedLoan.getTitle().toString());
                   System.out.println(selectedLoan.getId());
                   System.out.println(selectedLoan.getAuthor());
                   System.out.println(selectedLoan.getTitle());
                   System.out.println((selectedLoan.getPrice()));   
        //             lenderFld.setText(selectedLoan.getTitle().toString());
          //           authorFld.setText(selectedLoan.getAuthor().toString());
            //     loanamountFld.setText(Double.toString(selectedLoan.getPrice()));


               loanIdFld.setText("1234");
               lenderFld.setText("Test LoaN NAME");
               authorFld.setText("Test lender");
               loanamountFld.setText("Test loan amount");


                }
            }
            }

          }

          }

What I want is when someone clicks on the GridBagLayout's loanid instances, details about the loan are displayed. I can see that valueChanged() is called as "inside valueChanged. selectedListIndex" is printed but loanIdFld.setText("1234") does not update the LoadId text field with 1234. 1234 is a random number I inserted to determine if something can be displayed but that also is not shown. Some functions are not defined here, but there is no syntax error.

Answer 1

My guess: The loansController object that has the methods above called, that you set the text of its JTextFields, is not the same loansController object that is visualized by the user.

But without more information, this is just a guess.

Edit 1
Here is evidence that I may be right:

listSelectionModel.addListSelectionListener(new loansController(model));

You are creating a new loansController object as the listener rather than using this :

listSelectionModel.addListSelectionListener(this);

Edit 2
And now with the almost-SSCCE code below (too long to be a true SSCCE, but short enough), I have proven that my guess is in fact correct, that you are setting the text of the wrong object, of one that is not visualized. If you find the commented lines, comment out one line and uncomment the other to see the alteration in behavior:

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

@SuppressWarnings("serial")
public class loansController extends JFrame implements ActionListener,
         ListSelectionListener {
   private JButton addButton;
   private JButton deleteButton;
   private JButton viewDetailsButton;
   private JPanel btnsPnl = new JPanel();
   private JPanel mainPnl = new JPanel();
   private JPanel dataPnl = new JPanel();
   private JPanel listPnl = new JPanel();
   private JLabel loanIdLabel = new JLabel("LoanId");
   private JLabel loanName = new JLabel("Loan Name");
   private JTextField loanIdFld = new JTextField(15);
   private JTextField lenderFld = new JTextField(15);
   private JTextField loanamountFld = new JTextField(15);
   private DefaultListModel dlm = new DefaultListModel();
   private JList jlst = new JList(dlm);
   private int selectedListIndex;
   private ListSelectionModel listSelectionModel;

   public loansController() {
      addButton = new JButton("Add Loan");
      deleteButton = new JButton("Delete Loan");
      viewDetailsButton = new JButton("View Details of all Loans");
   }

   public void buildGUI() {
      String[] data = {"one", "two", "three", "four"};
      for (String datum : data) {
         dlm.addElement(datum);
      }
      GridBagLayout gbl = new GridBagLayout();
      GridBagConstraints gbc = new GridBagConstraints();
      gbc.gridx = 0;
      gbc.gridy = 0;
      dataPnl.setLayout(new GridLayout(4, 2));
      dataPnl.add(loanIdLabel);
      dataPnl.add(loanIdFld);
      dataPnl.add(loanName);
      dataPnl.add(lenderFld);
      dataPnl.add(loanamountFld);
      gbl.setConstraints(dataPnl, gbc);
      mainPnl.add(dataPnl);
      Dimension listDim = new Dimension(50, 90);
      jlst.setPreferredSize(listDim);
      gbc.gridx = 0;
      gbc.gridy = 1;
      gbl.setConstraints(listPnl, gbc);
      listPnl.add(jlst);
      listSelectionModel = jlst.getSelectionModel();


      // ****** here, comment one line and uncomment the other
      listSelectionModel.addListSelectionListener(new loansController());
      // !! listSelectionModel.addListSelectionListener(this);


      gbc.gridx = 1;
      gbc.gridy = 1;
      gbc.gridwidth = 2;
      gbl.setConstraints(btnsPnl, gbc);
      addButton.addActionListener(this);
      deleteButton.addActionListener(this);
      viewDetailsButton.addActionListener(this);
      btnsPnl.add(addButton);
      btnsPnl.add(deleteButton);
      btnsPnl.add(viewDetailsButton);
      mainPnl.add(listPnl);
      mainPnl.add(btnsPnl);
      getContentPane().add(mainPnl);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setSize(800, 400);
      setVisible(true);
   }

   public void actionPerformed(ActionEvent ae) {
      if (ae.getSource() == addButton) {
      } else if (ae.getSource() == deleteButton) {
      } else if (ae.getSource() == viewDetailsButton) {
      }
   }

   /*
    * This method clears the text field after the action Performed method for
    * the add and delete Buttons
    */
   public void setClearTextFld() {
      loanIdFld.setText("");
      lenderFld.setText("");
      loanamountFld.setText("");
   }

   public void valueChanged(ListSelectionEvent e) {
      listSelectionModel = (ListSelectionModel) e.getSource();
      int maxselectedListIndex = listSelectionModel.getMaxSelectionIndex();
      int minselectedListIndex = listSelectionModel.getMinSelectionIndex();
      System.out.println(selectedListIndex);
      if (!listSelectionModel.isSelectionEmpty()) {
         for (int i = minselectedListIndex; i <= maxselectedListIndex; i++) {
            if (listSelectionModel.isSelectedIndex(i)) {
               selectedListIndex = i;
               System.out.println("inside valueChanged. selectedListIndex");
               System.out.println(selectedListIndex);
               loanIdFld.setText("1234");
               lenderFld.setText("Test LoaN NAME");
               loanamountFld.setText("Test loan amount");
            }
         }
      }
   }

   public static void main(String[] args) {
      loansController controller = new loansController();
      controller.buildGUI();
   }
}

Note that this is what you should be doing: simplifying your code until you isolate the problem as it allows you to solve it much more easily, and failing that, then if you post this compilable runnable code, it lets us help you solve it more easily. This process is called creating an SSCCE or Short, Self Contained, Correct (Compilable), Example

Edit 3
A better SSCCE:

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

@SuppressWarnings("serial")
public class loansController extends JFrame implements ListSelectionListener {
   private JPanel mainPnl = new JPanel();
   private JPanel dataPnl = new JPanel();
   private JPanel listPnl = new JPanel();
   private JTextField loanIdFld = new JTextField(15);
   private JTextField lenderFld = new JTextField(15);
   private JTextField loanamountFld = new JTextField(15);
   private DefaultListModel dlm = new DefaultListModel();
   private JList jlst = new JList(dlm);
   private ListSelectionModel listSelectionModel;

   public void buildGUI() {
      String[] data = {"one", "two", "three", "four"};
      for (String datum : data) {
         dlm.addElement(datum);
      }
      dataPnl.setLayout(new GridLayout(4, 2));
      dataPnl.add(loanIdFld);
      dataPnl.add(lenderFld);
      dataPnl.add(loanamountFld);
      mainPnl.add(dataPnl);
      Dimension listDim = new Dimension(50, 90);
      jlst.setPreferredSize(listDim);
      listPnl.add(new JScrollPane(jlst));
      listSelectionModel = jlst.getSelectionModel();

      // ****** here, comment one line and uncomment the other
      // !! listSelectionModel.addListSelectionListener(new loansController());
      listSelectionModel.addListSelectionListener(this);

      mainPnl.add(listPnl);
      getContentPane().add(mainPnl);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      pack();
      setLocationRelativeTo(null);
      setVisible(true);
   }

   public void valueChanged(ListSelectionEvent e) {
      System.out.println("inside valueChanged. ");
      loanIdFld.setText("1234");
      lenderFld.setText("Test LoaN NAME");
      loanamountFld.setText("Test loan amount");
   }

   public static void main(String[] args) {
      new loansController().buildGUI();
   }
}