JComboBox从ArrayList-不工作-Java摇摆

Question

我仍然在玩Java和秋千（对这一切还是很陌生的）。我试图填充一个JComboBox与数据从. txt文件。我将数据拉入ArrayList，并试图用ArrayList变量填充JComboBox。然而，当我运行应用程序时，组合框是空白的。

这是数组代码：

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

文件读取器代码：

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();
         }
     }

我用来做组合盒的混乱：

 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); 

    }

这个类的整个混乱的代码。

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); 

    }      







}

你知道我哪里出错了吗？

Answer 1

Taka仔细看看你做事情的顺序。。。

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

首先，您调用reportInterface，它初始化您的框架...

其次，调用allReportsBtn，创建按钮...

第三，您调用comboBox，它将List的内容应用到您的组合框，该组合框是空的...

第四，调用fileRead，它从文件中读取值。。。

您提供给JComboBox的数组与您读取的文件值的列表之间没有关系，因此即使您告诉combobox值已更改，它也不会看到更改

试着做一些更像

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

反而...

Answer 2

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

正如奥比切雷所指出的那样：

1. 首先调用comboBox（），它创建组合框并用空List填充组合框。
2. 然后调用fileRead（）方法，该方法将数据添加到List中，但这不会更新组合框的模型。

代码顺序需要颠倒：

fileRead();
comboBoxes();