我有2个Jcombo Box：combo1和combo2
我选择了combo1，我可以获得combo2的信息但问题是我可以获得combo2的信息，但它没有更新。我也尝试使用updata.UI（）但它没有帮助。
这是旁边的代码
public void actionPerformed(ActionEvent e) {
JComboBox cb = (JComboBox)e.getSource();
String uname1 = (String)cb.getSelectedItem();
combo2 = update(uname1);
combo2.updateUI();
}
这是更新内的代码
protected JComboBox update(String name) {
JComboBox tmp = new JComboBox();
//Read Content from XML file (University is bigger than Year)
NodeList nList = doc.getElementsByTagName("University");
System.out.println("Inside Fn " + name);
for(int i = 0 ; i < nList.getLength();i++) {
Element el = (Element)nList.item(i);
if(name.contentEquals(el.getAttributeNode("name").getNodeValue()))
{
NodeList tmpyList = el.getElementsByTagName("Year");
for(int j = 0 ; j < tmpyList.getLength();j++)
{
Element yl = (Element)tmpyList.item(j);
System.out.println(yl.getAttribute("yr"));
tmp.addItem(yl.getAttribute("yr"));
}
}
}
return tmp; //Return ComboBox to combo2
}
感谢您的善意，我尝试使用您的代码，但它不起作用（它仍然没有更新），请帮帮我
这是我的构造函数
public JFrameExample() {
String[] comboboxdefault = { "Select" };
JComboBox combo1 = Universitylist();
JComboBox combo2 = new JComboBox(comboboxdefault);
JComboBox combo3 = new JComboBox(comboboxdefault);
uList.addActionListener(this);
yList.addActionListener(this);
dList.addActionListener(this);
JPanel student_information = new JPanel(new GridLayout(0,1));
uList.setName("University List");
yList.setName("Year List");
// University List
student_information.add(combo1);
// Database Year List
student_information.add(combo2);
// Programme List
student_information.add(combo3);
//Add Components to this container, using the default FlowLayout.
add(student_information);
}
这是combo2更新它返回String Array
protected String[] updateyList(String name)
{
String[] tmp = null;
//Read from XML file
for(int i = 0 ; i < nList.getLength();i++) {
Element el = (Element)nList.item(i);
if(name.contentEquals(el.getAttributeNode("name").getNodeValue()))
{
NodeList tmpyList = el.getElementsByTagName("Year");
tmp = new String[tmpyList.getLength()];
for(int j = 0 ; j < tmpyList.getLength();j++)
{
Element yl = (Element)tmpyList.item(j);
//Add to String Array
tmp[j] = yl.getAttribute("yr");
}
}
}
return tmp;
}
在行动中执行
public void actionPerformed(ActionEvent e) {
JComboBox cb = (JComboBox)e.getSource();
String uname1 = (String)cb.getSelectedItem();
System.out.println(cb.getName()); // To make sure I got the combo1.
try {
//I change to the model method
DefaultComboBoxModel model = new DefaultComboBoxModel( updateyList(uname1) );
System.out.println(model.getSize());
combo2 = new JComboBox(); // If I don't have this line it will throw error Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
combo2.setModel(model);
} catch (ParserConfigurationException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (SAXException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
这是用于创建GUI功能
private static void createAndShowLoginGUI() {
//Create and set up the window.
JFrame frame = new JFrame("Login");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JFrameExample newContentPane = new JFrameExample();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
这是主要功能
public static void main(String[] args)
{
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowLoginGUI();
}
});
}
我认为我做错了但我不知道在哪里
答案 0 :(得分：3)
无需使用updateUI（）方法。
如果要更改第二个组合框中的数据，则应更改模型（不要创建新的组合框）：
comboBox2.setModel(...);
它将自动重绘自己。您可以创建DefaultComboBoxModel并直接向其添加数据。
编辑：
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class ComboBoxTwo extends JFrame implements ActionListener
{
private JComboBox mainComboBox;
private JComboBox subComboBox;
private Hashtable subItems = new Hashtable();
public ComboBoxTwo()
{
String[] items = { "Select Item", "Color", "Shape", "Fruit" };
mainComboBox = new JComboBox( items );
mainComboBox.addActionListener( this );
// prevent action events from being fired when the up/down arrow keys are used
mainComboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);
getContentPane().add( mainComboBox, BorderLayout.WEST );
// Create sub combo box with multiple models
subComboBox = new JComboBox();
subComboBox.setPrototypeDisplayValue("XXXXXXXXXX"); // JDK1.4
getContentPane().add( subComboBox, BorderLayout.EAST );
String[] subItems1 = { "Select Color", "Red", "Blue", "Green" };
subItems.put(items[1], subItems1);
String[] subItems2 = { "Select Shape", "Circle", "Square", "Triangle" };
subItems.put(items[2], subItems2);
String[] subItems3 = { "Select Fruit", "Apple", "Orange", "Banana" };
subItems.put(items[3], subItems3);
// mainComboBox.setSelectedIndex(1);
}
public void actionPerformed(ActionEvent e)
{
String item = (String)mainComboBox.getSelectedItem();
Object o = subItems.get( item );
if (o == null)
{
subComboBox.setModel( new DefaultComboBoxModel() );
}
else
{
subComboBox.setModel( new DefaultComboBoxModel( (String[])o ) );
}
}
public static void main(String[] args)
{
JFrame frame = new ComboBoxTwo();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible( true );
}
}
答案 1 :(得分：2)
正如您现在所做的那样，每次都会重新创建组合框（通过在update方法中返回tmp）。这似乎没有反映在UI中，也许其他人会发布原因。但是，如果您可以更改以更新组合值（更改模型或删除当前值并添加新值）而不是重新创建，那么以下帖子可以帮助您Dynamically change JComboBox