如何從另一個類中獲取ArrayList以顯示在JComboBox中？

Question

我正在嘗試構建程序， 但無法從另一個類中獲取ArrayList使其顯示在JComboBox中。 我的程序看起來像這樣，但是在編寫“ Melissa”之前，我想擁有一個JComboBox，該列表具有一個用戶列表，並能夠從中選擇以獲得結果：

更新這是我的錯誤：

 ----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.

這是我不完整的代碼，由於無法找到我的arrayList而給我一個錯誤：

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);
    }
}

這是我的另一個包含ArrayList的面板的代碼：

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);
    }
}

這是用於制作ArrayList的User類：

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，您最好從歷史記錄主目錄調用用戶管理器模塊，例如

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

    manageUsers();

這將啟動兩個JPanels，因此您可以同時管理用戶和觀看歷史記錄。

另外，

// 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);
}

還有一件事，一旦初始化用戶列表，您就需要附加一個監聽器，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) {
        }
    });

通過這兩項更正，您將能夠在組合框中列出用戶名，並且用戶列表的動態更改將反映到該框中的列表中。

干杯。

Answer 2

讓我在這里上傳整個源代碼

1. User.java-源代碼隨即出現（我不知道為什么它們不符合要求。）

   打包用戶選擇列表;

   公共類用戶{

   私有字符串userName; private int積分= 0;

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

   public User（）{userName =“”; }

   公共無效setUserName（String userName）{this.userName = userName;
   }

   public String getUserName（）{return userName; }

   公共無效addPoints（int chorePoints）{點+ = chorePoints; }}

2. ManageUsersGUI.java －緊隨其后的是源代碼（我不知道為什么它們還是再次出現。）

   打包用戶選擇列表;

   導入javax.swing。 ; 導入java.awt。 ; 導入java.awt.event。*; 導入java.util.ArrayList; 導入javax.swing.JCheckBox;

   公共類ManageUsersGUI擴展了JPanel {公共靜態ArrayList用戶=新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); } // 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); } 

   }

3. UserHistory.java-源代碼隨即出現（我不知道為什么它們不合常規，第三次也是最后一次出現。）

   導入java.awt。 ; 導入javax.swing。 ; 導入javax.swing.event.PopupMenuEvent; 導入javax.swing.event.PopupMenuListener; 導入userchorelist.ManageUsersGUI; 導入靜態userchorelist.ManageUsersGUI.manageUsers; 導入靜態userchorelist.ManageUsersGUI.users; 導入userchorelist.User;

   公共類UserHistory擴展了JPanel {private JLabel jcomp1; 私人JComboBox userList; 私人JLabel jcomp3; 私有JTextField selectedUser; 私人JLabel jcomp5; 私人JTextField pointsEarned; 私人JLabel jcomp7; 私人JList choresCompleted;

    public UserHistory() { //construct preComponents String[] userListItems = new String[users.size()]; String[] choresCompletedItems = {"Item 1", "Item 2", "Item 3"}; //construct components jcomp1 = new JLabel ("User History"); 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) { } }); 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); manageUsers(); } 

   }

Answer 3

我建議您在類UserHistory和ManageUsersGUI添加作為顯式參數接收用戶列表：

class UserHistory
{
    private final List<User> users;

    public UserHistory(List<User> users)
    {
        super();
        this.users=users;
        ...
    }
}

class ManageUsersGUI
{
    private final List<User> users;

    public UserHistory(List<User> users)
    {
        super();
        this.users=users;
        ...
    }
}

然后，您可以創建一個唯一的用戶列表作為外部類，例如UserManagement ，並使其成為單例 ：

public class UserManagement
{
    private static final UserManagement INSTANCE=new UserManagement();

    private final List<User> list=new ArrayList<User>();

    public static UserManagement getInstance()
    {
        return INSTANCE;
    }

    private UserManagement()
    {
    }

    public List<User> getUsers()
    {
        return users;
    }
}

然后，在main方法中同時實例化兩個類時，必須提供用戶列表（以及將來可能出現的實例化）：

public static void main (String[] args) {
    ...
    UserManagement.getInstance().getUsers().add("winkum");
    UserManagement.getInstance().getUsers().add("blinkum");
    UserManagement.getInstance().getUsers().add("nod");
    frame.getContentPane().add (new UserHistory(UserManagement.getInstance().getUsers()));
    ...
}