JList添加第一个元素非常慢

Question

我正在向带有DefaultListModel的JList添加一个字符串，它需要几秒钟才能出现。 有时，我可能需要单击JList才能显示列表。

我正在使用 Eclipse Indigo。 当我在将元素添加到 JList 后设置断点时，执行速度很快。

我在网上搜索了JList，他们都在谈论向列表中添加许多项目。 我正在将第一个元素添加到列表中。

这是我的代码片段：

private DefaultListModel function_list_model = new DefaultListModel();
private JList list_functions = new JList(function_list_model);
//...
// Initialization code:
JPanel panel_function_list = new JPanel();
panel_function_list.setBounds(10, 53, 541, 220);
panel_functions.add(panel_function_list);
panel_function_list.setLayout(null);
JLabel lblFunctions = new JLabel("Functions");
lblFunctions.setHorizontalAlignment(SwingConstants.CENTER);
lblFunctions.setBounds(235, 11, 99, 14);
panel_function_list.add(lblFunctions);
list_functions.setBorder(new LineBorder(new Color(0, 0, 0)));
list_functions.setBounds(10, 42, 492, 177);
list_functions.setFont(new Font("Courier New", Font.PLAIN, 12));
list_functions.setPreferredSize(new Dimension(0, 150));
list_functions.setMinimumSize(new Dimension(32767, 100));
list_functions.setMaximumSize(new Dimension(32767, 100));
JScrollPane scrollPane_functions = new JScrollPane(list_functions);
scrollPane_functions.setBounds(10, 79, 541, 183);
panel_functions.add(scrollPane_functions);
// Code to add a string:  
String burger = new String("burger");
function_list_model.addElement(burger);

我也在将 WindowBuilder 与 Eclipse 一起使用。

那么如何提高JList的性能呢？

Answer 1

如果你愿意，我可以从Char[]生成新的Item并调用doClick()JButton("Fire")

import java.awt.*;
import java.awt.event.*;
import java.util.Date;
import javax.swing.*;
import javax.swing.event.*;
public class ListDemo extends JPanel implements ListSelectionListener {
private JList list;
private DefaultListModel listModel;
private static final String hireString = "Hire";
private static final String fireString = "Fire";
private JButton fireButton;
private JTextField employeeName;
private javax.swing.Timer timer = null;
private int delay = 3;
private int count = 0;
public ListDemo() {
super(new BorderLayout());
listModel = new DefaultListModel();
listModel.addElement("Jane Doe");
listModel.addElement("John Smith");
listModel.addElement("Kathy Green");
list = new JList(listModel);
list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
list.setSelectedIndex(0);
list.addListSelectionListener(this);
list.setVisibleRowCount(5);
JScrollPane listScrollPane = new JScrollPane(list);
JButton hireButton = new JButton(hireString);
HireListener hireListener = new HireListener(hireButton);
hireButton.setActionCommand(hireString);
hireButton.addActionListener(hireListener);
hireButton.setEnabled(false);
fireButton = new JButton(fireString);
fireButton.setActionCommand(fireString);
fireButton.addActionListener(new FireListener());
employeeName = new JTextField(10);
employeeName.addActionListener(hireListener);
employeeName.getDocument().addDocumentListener(hireListener);
String name = listModel.getElementAt(list.getSelectedIndex()).toString();
JPanel buttonPane = new JPanel();
buttonPane.setLayout(new BoxLayout(buttonPane, BoxLayout.LINE_AXIS));
buttonPane.add(fireButton);
buttonPane.add(Box.createHorizontalStrut(5));
buttonPane.add(new JSeparator(SwingConstants.VERTICAL));
buttonPane.add(Box.createHorizontalStrut(5));
buttonPane.add(employeeName);
buttonPane.add(hireButton);
buttonPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
add(listScrollPane, BorderLayout.CENTER);
add(buttonPane, BorderLayout.PAGE_END);
start();
System.out.println(new Date());
}
private void start() {
timer = new javax.swing.Timer(delay * 10, updateCol());
timer.start();
}
public Action updateCol() {
return new AbstractAction("text load action") {
private static final long serialVersionUID = 1L;
@Override
public void actionPerformed(ActionEvent e) {
listModel.addElement("Jane Doe");
listModel.addElement("John Smith");
listModel.addElement("Kathy Green");
list.ensureIndexIsVisible(listModel.getSize()-1);
count++;
if (count >= 500) {
timer.stop();
System.out.println("update cycle completed");
System.out.println(new Date());
}
}
};
}
class FireListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
int index = list.getSelectedIndex();
listModel.remove(index);
int size = listModel.getSize();
if (size == 0) { //Nobody's left, disable firing.
fireButton.setEnabled(false);
} else { //Select an index.
if (index == listModel.getSize()) {
index--;
}
list.setSelectedIndex(index);
list.ensureIndexIsVisible(index);
}
}
}
class HireListener implements ActionListener, DocumentListener {
private boolean alreadyEnabled = false;
private JButton button;
HireListener(JButton button) {
this.button = button;
}
@Override
public void actionPerformed(ActionEvent e) {
String name = employeeName.getText();
if (name.isEmpty() || alreadyInList(name)) {
Toolkit.getDefaultToolkit().beep();
employeeName.requestFocusInWindow();
employeeName.selectAll();
return;
}
int index = list.getSelectedIndex(); //get selected index
if (index == -1) { //no selection, so insert at beginning
index = 0;
} else {           //add after the selected item
index++;
}
listModel.insertElementAt(employeeName.getText(), index);
//listModel.addElement(employeeName.getText());
employeeName.requestFocusInWindow();
employeeName.setText("");
list.setSelectedIndex(index);
list.ensureIndexIsVisible(index);
}
protected boolean alreadyInList(String name) {
return listModel.contains(name);
}
@Override
public void insertUpdate(DocumentEvent e) {
enableButton();
}
@Override
public void removeUpdate(DocumentEvent e) {
handleEmptyTextField(e);
}
@Override
public void changedUpdate(DocumentEvent e) {
if (!handleEmptyTextField(e)) {
enableButton();
}
}
private void enableButton() {
if (!alreadyEnabled) {
button.setEnabled(true);
}
}
private boolean handleEmptyTextField(DocumentEvent e) {
if (e.getDocument().getLength() <= 0) {
button.setEnabled(false);
alreadyEnabled = false;
return true;
}
return false;
}
}
@Override
public void valueChanged(ListSelectionEvent e) {
if (e.getValueIsAdjusting() == false) {
if (list.getSelectedIndex() == -1) {
fireButton.setEnabled(false);
} else {
fireButton.setEnabled(true);
}
}
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("ListDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JComponent newContentPane = new ListDemo();
newContentPane.setOpaque(true);
frame.setContentPane(newContentPane);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
createAndShowGUI();
}
});
}
}