java - 如何从另一个类获取 ArrayList 以显示在 JComboBox 中？

Question

我正在尝试构建一个程序，我无法从另一个类获取 ArrayList 以显示在 JComboBox 中。我的程序看起来像这样，但在“Melissa”所在的位置之前编写，我想要一个包含用户列表的 JComboBox，并能够从中进行选择以获取结果:

更新这是我的错误:

 ----jGRASP exec: javac -g UserHistory.java

UserHistory.java:20: error: cannot find symbol
        String[] userListItems = users.toArray(new String[0]);
                                 ^
  symbol:   variable users
  location: class UserHistory
Note: UserHistory.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error

 ----jGRASP wedge2: exit code for process is 1.
 ----jGRASP: operation complete.

这是我不完整的代码，它给我一个错误，因为它无法找到我的 arrayList:

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

public class UserHistory extends JPanel {
    private JLabel jcomp1;
    private JComboBox userList;
    private JLabel jcomp3;
    private JTextField selectedUser;
    private JLabel jcomp5;
    private JTextField pointsEarned;
    private JLabel jcomp7;
    private JList choresCompleted;

    public UserHistory() {
        //construct preComponents
        String[] userListItems = users.toArray(new String[0]);
        String[] choresCompletedItems = {"Item 1", "Item 2", "Item 3"};

        //construct components
        jcomp1 = new JLabel ("User History");
        userList = new JComboBox(userListItems);
        jcomp3 = new JLabel ("Below are the results of : ");
        selectedUser = new JTextField (5);
        jcomp5 = new JLabel ("Total points earned: ");
        pointsEarned = new JTextField (5);
        jcomp7 = new JLabel ("List of chores completed: ");
        choresCompleted = new JList (choresCompletedItems);

        //set components properties
        userList.setToolTipText ("Select a user");

        //adjust size and set layout
        setPreferredSize (new Dimension (465, 343));
        setLayout (null);

        //add components
        add (jcomp1);
        add (userList);
        add (jcomp3);
        add (selectedUser);
        add (jcomp5);
        add (pointsEarned);
        add (jcomp7);
        add (choresCompleted);

        //set component bounds (only needed by Absolute Positioning)
        jcomp1.setBounds (120, 20, 70, 25);
        userList.setBounds (210, 20, 100, 25);
        jcomp3.setBounds (95, 70, 155, 25);
        selectedUser.setBounds (245, 70, 100, 25);
        jcomp5.setBounds (125, 105, 140, 25);
        pointsEarned.setBounds (245, 105, 100, 25);
        jcomp7.setBounds (95, 140, 160, 25);
        choresCompleted.setBounds (245, 145, 100, 75);
    }


    public static void main (String[] args) {
        JFrame frame = new JFrame ("UserHistory");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add (new UserHistory());
        frame.pack();
        frame.setVisible (true);
    }
}

这是我包含 ArrayList 的另一个面板的代码:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import javax.swing.JCheckBox;

public class ManageUsersGUI extends JPanel {
    public ArrayList<User> users = new ArrayList<>();

    private JLabel addNewUserLabel;
    private JTextField addNewUserTextField;
    private JLabel deleteUsersLabel;
    private JButton addButton;
    private JButton deleteButton;
    private JPanel namePanel;


    public ManageUsersGUI() {
        //construct components
        addNewUserLabel = new JLabel ("Add new User here:");
        addNewUserTextField = new JTextField (0);
        deleteUsersLabel = new JLabel ("Select which User(s) you would like to delete:");
        addButton = new JButton ("Add");
        deleteButton = new JButton ("Delete");
        namePanel = new JPanel();
        namePanel.setLayout(new BoxLayout(namePanel, BoxLayout.Y_AXIS));

        //set components properties
        addNewUserTextField.setToolTipText ("Enter name and click on Add button.");
        addButton.setToolTipText ("Click here to Add new user.");
        deleteButton.setToolTipText ("Click here to delete User(s) selected.");

        //adjust size and set layout
        setPreferredSize (new Dimension (580, 485));
        setLayout (null);

        //add components
        add (addNewUserLabel);
        add (addNewUserTextField);
        add (deleteUsersLabel);
        add (namePanel);
        add (addButton);
        add (deleteButton);

        //set component bounds (only needed by Absolute Positioning)
        addNewUserLabel.setBounds (85, 130, 120, 25);
        addNewUserTextField.setBounds (235, 130, 125, 25);
        deleteUsersLabel.setBounds (135, 225, 281, 25);
        addButton.setBounds (385, 130, 100, 25);
        namePanel.setBounds(225, 270, 140, 0);
        deleteButton.setBounds (230, 335, 100, 25);

        addButton.addActionListener(new AddButtonListener());

        deleteButton.addActionListener(new DeleteButtonListener());
    }

    public ArrayList<User> getUser() {
               return users;
            }        

    private class AddButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            String text = addNewUserTextField.getText();
            users.add(new User(text));

            // Display the changes.
            JOptionPane.showMessageDialog(null, text + " has been added.");

            JCheckBox nameCheckBox = new JCheckBox();
            nameCheckBox.setText(addNewUserTextField.getText());
            namePanel.add(nameCheckBox);
            namePanel.setBounds(225, 270, 140, namePanel.getHeight() + 25);
            deleteButton.setBounds(230, deleteButton.getY() + 25, 100, 25);
            JFrame frame = (JFrame) getRootPane().getParent();
            frame.setSize(frame.getWidth(), frame.getHeight() + 25);
            frame.pack(); 

        }
    }

    private class DeleteButtonListener implements ActionListener {
         @Override
         public void actionPerformed(ActionEvent e) {
            for(Component component : namePanel.getComponents()) {
               if(component instanceof JCheckBox) {
                  if(((JCheckBox)component).isSelected())
                     namePanel.remove(component);
               }
            }
            namePanel.revalidate();
            namePanel.repaint();
         }   
    }


    public static void main (String[] args) {
        JFrame frame = new JFrame ("AddUsersPanel1");
        frame.setTitle("Manage Users");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add (new ManageUsersGUI());
        frame.pack();
        frame.setVisible (true);
    }
}

这是我用来制作 ArrayList 的 User 类:

public class User {

   private String userName;
   private int points = 0;

   public User(String userName) {
      this.userName = userName;
   }

   public User() {
      userName = "";
   }   

   public void setUserName(String userName) {
      this.userName = userName;   
   }

   public String getUserName() {
      return userName;
   }

   public void addPoints(int chorePoints) {
      points += chorePoints;
   }

  // public String toString() {
     // return userName + "\n";
 //  }

} 

Answer 1

首先，您最好从历史记录主调用用户管理器模块，例如

    JFrame frame = new JFrame ("UserHistory");
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add (new UserHistory());
    frame.pack();
    frame.setVisible (true);

    manageUsers();

这将启动两个 JPanel，以便您可以同时管理用户和观看历史记录。

此外，

// in ManageUsersGUI
public static void manageUsers() {
    JFrame frame = new JFrame ("AddUsersPanel1");
    frame.setTitle("Manage Users");
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add (new ManageUsersGUI());
    frame.pack();
    frame.setVisible (true);
}

还有一件事，一旦初始化用户列表，您就需要附加一个监听器，如下所示:

    userList = new JComboBox(userListItems);

    userList.addPopupMenuListener(new PopupMenuListener() {
        @Override
        public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
            userList.removeAllItems();
            for (User user: users) {
                userList.addItem(user.getUserName());
            }   
        }

        @Override
        public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
        }

        @Override
        public void popupMenuCanceled(PopupMenuEvent e) {
        }
    });

这两个更正将使您能够在组合框中列出用户名，并且用户列表的动态更改将反射(reflect)到框中的列表中。

干杯。