将元素添加到DefaultListModel时JList不更新
房子昂
问题内容：
问题答案：
我正在尝试创建一个简单的程序来管理员工。尝试添加新员工时，我似乎无法让该员工显示在Jlist上。
主机…
public class EmployeeFrame extends JFrame implements ActionListener {
// The buttons to display
private JButton addButton;
private JButton editButton;
private JButton deleteButton;
private JButton saveButton;
// The underlying list of employees, and the GUI object to display them
private DefaultListModel<Employee> listModel;
private JList<Employee> employeeList;
public static final String SAVE_FILE = "employees.txt";
/**
* Creates and displays a new EmployeeFrame. The program exits when the
* window is closed.
*/
public EmployeeFrame() {
// Basic window features
super("Employee Manager");
setLocationByPlatform(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
// Try to make it look like a native application -- using try/multi-catch
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException
| UnsupportedLookAndFeelException e) {
e.printStackTrace();
}
// Initialise an empty list model, a JList to display it, and a scroll
// pane to contain the list
listModel = new DefaultListModel<>();
employeeList = new JList<>(listModel);
JScrollPane employeeScroll = new JScrollPane(employeeList);
employeeScroll.setBorder(new TitledBorder("Employee List"));
// Initialise all buttons and add the current class as an action
// listener to all
addButton = new JButton("Add Employee");
addButton.addActionListener(this);
editButton = new JButton("Edit Employee");
editButton.addActionListener(this);
deleteButton = new JButton("Delete Employee");
deleteButton.addActionListener(this);
saveButton = new JButton("Save Employee List");
saveButton.addActionListener(this);
// Lay out the buttons in a line
Box topBox = Box.createHorizontalBox();
topBox.add(addButton);
topBox.add(Box.createHorizontalStrut(10));
topBox.add(editButton);
topBox.add(Box.createHorizontalStrut(10));
topBox.add(deleteButton);
topBox.add(Box.createHorizontalStrut(10));
topBox.add(saveButton);
// Lay out the window
getContentPane().setLayout(new BorderLayout());
getContentPane().add(topBox, BorderLayout.NORTH);
getContentPane().add(employeeScroll, BorderLayout.CENTER);
pack();
}
public DefaultListModel<Employee> getListModel() {
return this.listModel;
}
@Override
public void actionPerformed(ActionEvent event) {
// Determine which button was pushed
Object source = event.getSource();
// Here's what to do with the delete button
if (source == deleteButton) {
Employee selection = employeeList.getSelectedValue();
if (selection != null) {
listModel.removeElement(selection);
}
}
if (source == addButton) {
AddEmployeeDialog frame = new AddEmployeeDialog(new EmployeeFrame());
frame.setVisible(true);
}
}
public static void main(String[] args) {
new EmployeeFrame().setVisible(true);
}
}
添加员工的对话…
public class AddEmployeeDialog extends JDialog implements ActionListener {
// Common fields
private JComboBox<String> workerType;
private JTextField givenNameField;
private JTextField familyNameField;
private JDatePicker startDatePicker;
// Fields that depend on the employee type
private JTextField rateField;
private JTextField hoursField;
private JTextField salaryField;
// Buttons
private JButton okButton;
private JButton cancelButton;
// The employee frame -- used to position the dialog and to access the
// employee list
private EmployeeFrame employeeFrame;
public AddEmployeeDialog(final EmployeeFrame frame) {
// Basic initialisation
super(frame, "Add Employee", true);
setLocationRelativeTo(employeeFrame);
this.employeeFrame = frame;
// Common fields
workerType = new JComboBox<String>(Employee.getEmployeeTypes());
givenNameField = new JTextField(20);
familyNameField = new JTextField(20);
startDatePicker = new JDateComponentFactory().createJDatePicker();
// Fields only for hourly workers
rateField = new JTextField(10);
hoursField = new JTextField(5);
// Field only for salaried worker
salaryField = new JTextField(10);
// Top line
Box workerBox = Box.createHorizontalBox();
workerBox.add(new JLabel("Worker type"));
workerBox.add(workerType);
workerBox.add(new JLabel("Start date"));
workerBox.add((JPanel) startDatePicker);
// Next lines (names)
Box givenNameBox = Box.createHorizontalBox();
givenNameBox.add(new JLabel("Given name "));
givenNameBox.add(givenNameField);
Box familyNameBox = Box.createHorizontalBox();
familyNameBox.add(new JLabel("Family name"));
familyNameBox.add(familyNameField);
// Hourly-worker fields
Box hourlyBox = Box.createHorizontalBox();
hourlyBox.setBorder(new TitledBorder("Hourly worker information"));
hourlyBox.add(new JLabel("Rate"));
hourlyBox.add(rateField);
hourlyBox.add(Box.createHorizontalStrut(10));
hourlyBox.add(new JLabel("Hours"));
hourlyBox.add(hoursField);
// Salaried-worker fields
Box salariedBox = Box.createHorizontalBox();
salariedBox.setBorder(new TitledBorder("Salaried worker information"));
salariedBox.add(new JLabel("Salary"));
salariedBox.add(salaryField);
// Ensure that only the appropriate fields are enabled, depending on the
// worker type chosen
workerType.addItemListener(new ItemListener() {
@Override
public void itemStateChanged(ItemEvent arg0) {
String type = (String) workerType.getSelectedItem();
salaryField.setEnabled("Salaried".equals(type));
rateField.setEnabled("Hourly".equals(type));
hoursField.setEnabled("Hourly".equals(type));
}
});
workerType.setSelectedItem(null);
// Create buttons and add the current class as an ActionListener
okButton = new JButton("OK");
okButton.addActionListener(this);
cancelButton = new JButton("Cancel");
cancelButton.addActionListener(this);
// Bottom row of GUI: buttons
Box bottomBox = Box.createHorizontalBox();
bottomBox.add(Box.createHorizontalGlue());
bottomBox.add(okButton);
bottomBox.add(Box.createHorizontalGlue());
bottomBox.add(cancelButton);
bottomBox.add(Box.createHorizontalGlue());
// Lay out the GUI
getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
getContentPane().add(workerBox);
getContentPane().add(givenNameBox);
getContentPane().add(familyNameBox);
getContentPane().add(hourlyBox);
getContentPane().add(salariedBox);
getContentPane().add(Box.createVerticalStrut(10));
getContentPane().add(bottomBox);
pack();
}
@Override
public void actionPerformed(ActionEvent event) {
// Convert the value from the date picker into a LocalDate
GregorianCalendar startDateValue = (GregorianCalendar) startDatePicker.getModel().getValue();
LocalDate startDate = startDateValue.toZonedDateTime().toLocalDate();
// Work out which button was pressed
Object source = event.getSource();
if (source == cancelButton) {
// Just close the window
dispose();
}
if (source == okButton) {
// Determine if the employee is hourly or salaried
if (workerType.getSelectedItem().toString() == "Salaried") {
// Create new salaried employee
if (salaryField.getText().matches("[0-9]+")) {
Employee employee = new SalariedEmployee(givenNameField.getText(),
familyNameField.getText(),
startDate,
Double.parseDouble(salaryField.getText()));
employeeFrame.getListModel().addElement(employee);
}
}
else {
// Create new hourly employee
if (rateField.getText().matches("[0-9]+") && hoursField.getText().matches("[0-9]+")) {
Employee employee = new HourlyEmployee(givenNameField.getText(),
familyNameField.getText(),
startDate,
Double.parseDouble(rateField.getText()),
Integer.parseInt(hoursField.getText()));
employeeFrame.getListModel().addElement(employee);
}
}
dispose();
}
}
}
这就是我用来添加员工的方法
employeeFrame.getListModel().addElement(employee);
我认为这是正确的方法，但似乎无效。任何帮助将不胜感激。
问题答案：
有两个问题，
第一个：
不好：if (workerType.getSelectedItem().toString() == "Salaried") {。使用equals（…）或equalsIgnoreCase（…）。理解==检查是否绝对不是您感兴趣的 引用 相等性。您需要 函数
相等性，这是方法要测试的。
所以： if ("Salaried".equalsIgnoreCase(workerType.getSelectedItem().toString())) {
第二：
AddEmployeeDialog frame = new AddEmployeeDialog(new EmployeeFrame());
您要传入一个 新的 EmployeeFrame对象，这意味着您正在为错误的EmployeeFrame更新列表模型。而是传递 可视化的
EmployeeFrame。
更改为：
AddEmployeeDialog frame = new AddEmployeeDialog(EmployeeFrame.this);
我创建的程序可以缩小您的代码，但仍然允许其运行并演示您的问题：
import java.awt.BorderLayout;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.TitledBorder;
@SuppressWarnings("serial")
public class EmployeeFrame extends JFrame implements ActionListener {
private JButton addButton;
private DefaultListModel<Employee> listModel;
private JList<Employee> employeeList;
public EmployeeFrame() {
super("Employee Manager");
setLocationByPlatform(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
listModel = new DefaultListModel<>();
employeeList = new JList<>(listModel);
JScrollPane employeeScroll = new JScrollPane(employeeList);
employeeScroll.setBorder(new TitledBorder("Employee List"));
addButton = new JButton("Add Employee");
addButton.addActionListener(this);
Box topBox = Box.createHorizontalBox();
topBox.add(addButton);
getContentPane().setLayout(new BorderLayout());
getContentPane().add(topBox, BorderLayout.NORTH);
getContentPane().add(employeeScroll, BorderLayout.CENTER);
pack();
}
public DefaultListModel<Employee> getListModel() {
return this.listModel;
}
@Override
public void actionPerformed(ActionEvent event) {
Object source = event.getSource();
if (source == addButton) {
// !! AddEmployeeDialog frame = new AddEmployeeDialog(new EmployeeFrame());
AddEmployeeDialog frame = new AddEmployeeDialog(EmployeeFrame.this);
frame.setVisible(true);
}
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new EmployeeFrame().setVisible(true);
}
});
}
}
@SuppressWarnings("serial")
class AddEmployeeDialog extends JDialog implements ActionListener {
private JComboBox<String> workerType;
private JTextField givenNameField;
private JTextField familyNameField;
private JButton okButton;
private JButton cancelButton;
private EmployeeFrame employeeFrame;
public AddEmployeeDialog(final EmployeeFrame frame) {
super(frame, "Add Employee", true);
setLocationRelativeTo(employeeFrame);
this.employeeFrame = frame;
workerType = new JComboBox<String>(Employee.getEmployeeTypes());
givenNameField = new JTextField(20);
familyNameField = new JTextField(20);
Box workerBox = Box.createHorizontalBox();
workerBox.add(new JLabel("Worker type"));
workerBox.add(workerType);
workerBox.add(new JLabel("Start date"));
Box givenNameBox = Box.createHorizontalBox();
givenNameBox.add(new JLabel("Given name "));
givenNameBox.add(givenNameField);
Box familyNameBox = Box.createHorizontalBox();
familyNameBox.add(new JLabel("Family name"));
familyNameBox.add(familyNameField);
workerType.setSelectedItem(null);
// Create buttons and add the current class as an ActionListener
okButton = new JButton("OK");
okButton.addActionListener(this);
cancelButton = new JButton("Cancel");
cancelButton.addActionListener(this);
Box bottomBox = Box.createHorizontalBox();
bottomBox.add(Box.createHorizontalGlue());
bottomBox.add(okButton);
bottomBox.add(Box.createHorizontalGlue());
bottomBox.add(cancelButton);
bottomBox.add(Box.createHorizontalGlue());
// Lay out the GUI
getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));
getContentPane().add(workerBox);
getContentPane().add(givenNameBox);
getContentPane().add(familyNameBox);
getContentPane().add(Box.createVerticalStrut(10));
getContentPane().add(bottomBox);
pack();
}
@Override
public void actionPerformed(ActionEvent event) {
Object source = event.getSource();
if (source == okButton) {
System.out.println("here");
System.out.println(workerType.getSelectedItem());
if ("Salaried".equalsIgnoreCase(workerType.getSelectedItem().toString())) {
Employee employee = new Employee("Salaried", givenNameField.getText(), familyNameField.getText());
employeeFrame.getListModel().addElement(employee);
} else {
Employee employee = new Employee("Hourly", givenNameField.getText(), familyNameField.getText());
employeeFrame.getListModel().addElement(employee);
}
}
dispose();
}
}
class Employee {
private static final String[] EMPLOYEE_TYPES = { "Salaried", "Hourly" };
private String givenName;
private String familyName;
private String type;
public Employee(String type, String givenName, String familyName) {
this.type = type;
this.givenName = givenName;
this.familyName = familyName;
}
public static String[] getEmployeeTypes() {
return EMPLOYEE_TYPES;
}
public String getGivenName() {
return givenName;
}
public String getFamilyName() {
return familyName;
}
public String getType() {
return type;
}
@Override
public String toString() {
return String.format("Employee: %s, %s %s", type, givenName, familyName);
}
}
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