以下是多文件项目代码的一部分。我只发布此代码，因为我不清楚为什么setText方法不起作用。并非所有此项目的代码都包含在内。
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");
}
}
}
}
}
我想要的是当有人点击GridBagLayout的loanid实例时，会显示有关贷款的详细信息。我可以看到valueChanged（）被调用为“inside valueChanged.selectedListIndex”，但loanIdFld.setText（“1234”）不会用1234更新LoadId文本字段.1234是我插入的随机数，用于确定是否可以显示，但也没有显示。这里没有定义某些函数，但没有语法错误。
答案 0 :(得分：3)
我的猜测：具有上述方法的loansController对象，您设置其JTextField的文本，与用户可视化的loanController对象不同。
但没有更多信息，这只是猜测。
编辑1
这证明我可能是对的：
listSelectionModel.addListSelectionListener(new loansController(model));
您正在创建新 loanController对象作为侦听器，而不是使用 this ：
listSelectionModel.addListSelectionListener(this);
编辑2
现在使用下面几乎是SSCCE代码（太长时间不能成为真正的SSCCE，但足够短），我已经证明我的猜测实际上是正确的，你正在设置错误对象的文本，而不是可视化。如果您找到注释行，请注释掉一行并取消注释另一行以查看行为的更改：
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();
}
}
请注意，这就是您应该做的事情：简化代码直到您将问题隔离开来，因为它允许您更轻松地解决问题，并且失败了，那么如果您发布这个可编译的可运行代码，它会让 us 可帮助您更轻松地解决问题。此过程称为创建SSCCE或Short, Self Contained, Correct (Compilable), Example
编辑3
更好的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();
}
}