更新JComboBox后，如何刷新框的长度

问题描述

我正在尝试创建一种更新JComboBox的方法，以便当用户在文本字段中输入内容时，一些代码将处理该条目并相应地更新JComboBox.我遇到的一个问题是我可以更新JComboBox，但是第一次打开它时，该盒子并没有刷新其中选项的长度，并且如下面的代码所示，它显示了额外的空白.我不知道是否有更好的其他方法可以做到这一点，但这就是我想出的.

I am trying to create a way to update a JComboBox so that when the user enters something into the text field, some code will process the entry and update the JComboBox accordingly.The one issue that I am having is I can update the JComboBox, but the first time it is opened, the box has not refresh the length of the options in it and as seen in the code below it displays extra white space. I do not know if there is a better different way to do this, but this is what I came up with.

感谢您的帮助，

丹

import java.awt.event.*;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Catch{
public static JComboBox dropDown;
public static String dropDownOptions[] = {
         "Choose",
         "1",
         "2",
         "3"};
 public static  void main(String[] args) {
     dropDown = new JComboBox(dropDownOptions);
     final JTextField Update = new JTextField("Update", 10);
     final JFrame frame = new JFrame("Subnet Calculator");
     final JPanel panel = new JPanel();
     frame.setSize(315,430);
     frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
     Update.addFocusListener(new FocusListener(){
    public void focusGained(FocusEvent arg0) {
            }
            public void focusLost(FocusEvent arg0) {
                dropDown.removeAllItems();
                dropDown.insertItemAt("0", 0);
                dropDown.insertItemAt("1", 1);
                dropDown.setSelectedIndex(0);
            }
              });
        panel.add(Update);
        panel.add(dropDown);
        frame.getContentPane().add(panel);
        frame.setVisible(true);
        Update.requestFocus();
        Update.selectAll();
    }
}

推荐答案

1)JTextField从ActionListener

2)删除FocusListener

3)关于从JTextField向JList添加最后一个Item的新Item的示例，只需要修改JComboBox并正确添加方法insertItemAt()

3) example about add new Item as last Item from JTextField to the JList, only you have to modify for JComboBox and add method insertItemAt() correctly

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

public class ListBottom2 {

    private static final long serialVersionUID = 1L;
    private JFrame frame = new JFrame();
    private DefaultListModel model = new DefaultListModel();
    private JList list = new JList(model);
    private JTextField textField = new JTextField("Use Enter to Add");
    private JPanel panel = new JPanel(new BorderLayout());

    public ListBottom2() {
        model.addElement("First");
        list.setVisibleRowCount(5);
        panel.setBackground(list.getBackground());
        panel.add(list, BorderLayout.SOUTH);
        JScrollPane scrollPane = new JScrollPane(panel);
        scrollPane.setPreferredSize(new Dimension(200, 100));
        frame.add(scrollPane);
        frame.add(textField, BorderLayout.NORTH);
        textField.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                JTextField textField = (JTextField) e.getSource();
                DefaultListModel model = (DefaultListModel) list.getModel();
                model.addElement(textField.getText());
                int size = model.getSize() - 1;
                list.scrollRectToVisible(list.getCellBounds(size, size));
                textField.setText("");
            }
        });
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ListBottom2 frame = new ListBottom2();
            }
        });
    }
}

这篇关于更新JComboBox后，如何刷新框的长度的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！