ArrayList中的JComboBox <String> -無法正常工作-Java Swing

Question

我仍在使用Java和swing（仍然很新）。 我正在嘗試使用.txt文件中的數據填充JComboBox。 我將數據拉入ArrayList，並嘗試使用ArrayList變量填充JComboBox。 但是，當我運行應用程序時，組合框為空白。

這是數組代碼：

private ArrayList<String> list = new ArrayList<String>();

文件閱讀器代碼：

private void fileRead(){
         try{
             Scanner scan = new Scanner(new File("Examiner.txt"));
            // ArrayList<String> list = new ArrayList<String>();
             while(scan.hasNext()){
                 list.add(scan.next());
             }
             scan.close();
         }
         catch (FileNotFoundException e){
             e.printStackTrace();
         }
     }

還有我用於組合框的爛攤子：

 private void comboBoxes(){                
        panel.setBorder(new EmptyBorder(0, 5, 5, 10));
        String[] comboBox1Array = list.toArray(new String[list.size()]);
        JComboBox comboBox1 = new JComboBox(comboBox1Array);          
        panel.add(examinerLabel);
        panel.add(comboBox1);          
        panel.add(viewTeachedCourses);
         JComboBox comboBox2 = new JComboBox();
         panel.add(courseLabel);         
         panel.add(comboBox2); 
         panel.add(viewPrograms);
         add(panel, BorderLayout.LINE_START); 

    }

此類的整個代碼。

package messing with swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.border.EmptyBorder;


public class ReportGUI extends JFrame{
    //Fields
    private JButton viewAllReports = new JButton("View All Program Details");
    private JButton viewPrograms = new JButton("View Programs and Majors Associated with this course"); 
    private JButton viewTeachedCourses = new JButton("View Courses this Examiner Teaches"); 
    private JLabel courseLabel = new JLabel("Select a Course: ");
    private JLabel examinerLabel = new JLabel("Select an Examiner: "); 
    private JPanel panel = new JPanel(new GridLayout(6,2,4,4));  
    private ArrayList<String> list = new ArrayList<String>();
    //private String storeAllString="";



     public ReportGUI(){   
       reportInterface();
       allReportsBtn();     
       comboBoxes();
       fileRead();
     }   



     private void fileRead(){
         try{
             Scanner scan = new Scanner(new File("Examiner.txt"));
            // ArrayList<String> list = new ArrayList<String>();
             while(scan.hasNext()){
                 list.add(scan.next());
             }
             scan.close();
         }
         catch (FileNotFoundException e){
             e.printStackTrace();
         }
     }

    private void reportInterface(){         
          setTitle("Choose Report Specifications");                   
          setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
          JPanel panel = new JPanel(new FlowLayout());        
          add(panel, BorderLayout.CENTER);
          setSize(650,200);
          setVisible(true);    
          setResizable(false);
          setLocationRelativeTo(null);
}    
    private void allReportsBtn(){
        JPanel panel = new JPanel(new GridLayout(1,1)); 
        panel.setBorder(new EmptyBorder(70, 50, 70, 25));
        panel.add(viewAllReports);        
        viewAllReports.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e){
                JFrame AllDataGUI = new JFrame();
                new AllDataGUI();
            }
        });         
        add(panel, BorderLayout.LINE_END);
    }       
    private void comboBoxes(){                
        panel.setBorder(new EmptyBorder(0, 5, 5, 10));
        String[] comboBox1Array = list.toArray(new String[list.size()]);
        JComboBox comboBox1 = new JComboBox(comboBox1Array);          
        panel.add(examinerLabel);
        panel.add(comboBox1);          
        panel.add(viewTeachedCourses);
         JComboBox comboBox2 = new JComboBox();
         panel.add(courseLabel);         
         panel.add(comboBox2); 
         panel.add(viewPrograms);
         add(panel, BorderLayout.LINE_START); 

    }      







}

有什么想法我要去哪里嗎？

Answer 1

 public ReportGUI()
 {   
   reportInterface();
   allReportsBtn();     
   comboBoxes();
   fileRead();
 }   

正如Obicere指出的那樣：

1. 您首先調用comboBoxes() ，它將創建組合框，並用一個空的List填充組合框。
2. 然后調用fileRead()方法，該方法會將數據添加到列表中，但這不會更新組合框的模型。

代碼順序需要顛倒：

fileRead();
comboBoxes();

Answer 2

塔卡仔細看看你做的順序...

public ReportGUI(){   
   reportInterface();
   allReportsBtn();     
   comboBoxes();
   fileRead();
 }   

首先，調用reportInterface ，這將初始化您的框架...

其次，調用allReportsBtn ，這將創建您的按鈕...

第三，調用comboBoxes ，它將List的內容應用於您的組合框，該組合框為空...

第四，調用fileRead ，從文件中讀取值...

提供給JComboBox與讀取的文件的值List之間沒有關系，因此，即使您告訴組合框值已更改，也不會看到該更改

嘗試做更多類似的事情

public ReportGUI(){   
   reportInterface();
   allReportsBtn();     
   fileRead();
   comboBoxes();
 }   

代替...