JList not updating when adding element to DefaultListModel

问题

I'm trying to create a simple program to manage Employees. When trying to add a new employee I can't seem to get the employee to be displayed on the Jlist.

The main frame...

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);
    }

}

The dialogue that adds the employee...

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();      
        }       
    }

}

This is what I'm using to add the employee

employeeFrame.getListModel().addElement(employee);

I think this is the right method but it doesn't seem to work. Any help will really be appreciated.

回答1:

Two problems,
The first:

bad: if (workerType.getSelectedItem().toString() == "Salaried") {. Use equals(...) or equalsIgnoreCase(...). Understand that == checks for reference equality which is most definitely not what you're interested in. You want functional equality which is what the methods test for.

So: if ("Salaried".equalsIgnoreCase(workerType.getSelectedItem().toString())) {

The second:

AddEmployeeDialog frame = new AddEmployeeDialog(new EmployeeFrame());

You're passing in a new EmployeeFrame object meaning you're updating the list model for the wrong EmployeeFrame. Instead pass in the visualized EmployeeFrame.

Change it to:

AddEmployeeDialog frame = new AddEmployeeDialog(EmployeeFrame.this);

My program that I created to shrink your code but still allow it to be runnable and to demonstrate your problem:

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);
    }

}

来源：https://stackoverflow.com/questions/34031086/jlist-not-updating-when-adding-element-to-defaultlistmodel