我个人建议使用弹出窗口或自定义JWindow 而不是JPopupMenu，因为后者最初仅用于仅显示菜单项。它通常适用于其他事情，但以不同方式使用它并不是最佳实践。
例如，您的示例中有几个菜单项作为自动完成选项 - 如果只有几个结果，它们就可以正常工作。但是如果有 10 个呢？如果是50呢？还是500？您必须以某种方式为这些情况创建额外的解决方法 - 将项目放入滚动窗格（哦天哪，这看起来很难看）或将结果减少到几个最好的（这也不是最好的选择）。
所以我做了一个小例子，使用JWindow 作为AutocompleteField 的弹出窗口。它非常简单，但做了一些您期望的基本操作以及您提到的那些：
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import java.awt.*;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
/**
* @author Mikle Garin
* @see https://stackoverflow.com/questions/45439231/implementing-autocomplete-with-jtextfield-and-jpopupmenu
*/
public final class AutocompleteField extends JTextField implements FocusListener, DocumentListener, KeyListener
{
/**
* {@link Function} for text lookup.
* It simply returns {@link List} of {@link String} for the text we are looking results for.
*/
private final Function<String, List<String>> lookup;
/**
* {@link List} of lookup results.
* It is cached to optimize performance for more complex lookups.
*/
private final List<String> results;
/**
* {@link JWindow} used to display offered options.
*/
private final JWindow popup;
/**
* Lookup results {@link JList}.
*/
private final JList list;
/**
* {@link #list} model.
*/
private final ListModel model;
/**
* Constructs {@link AutocompleteField}.
*
* @param lookup {@link Function} for text lookup
*/
public AutocompleteField ( final Function<String, List<String>> lookup )
{
super ();
this.lookup = lookup;
this.results = new ArrayList<> ();
final Window parent = SwingUtilities.getWindowAncestor ( this );
popup = new JWindow ( parent );
popup.setType ( Window.Type.POPUP );
popup.setFocusableWindowState ( false );
popup.setAlwaysOnTop ( true );
model = new ListModel ();
list = new JList ( model );
popup.add ( new JScrollPane ( list )
{
@Override
public Dimension getPreferredSize ()
{
final Dimension ps = super.getPreferredSize ();
ps.width = AutocompleteField.this.getWidth ();
return ps;
}
} );
addFocusListener ( this );
getDocument ().addDocumentListener ( this );
addKeyListener ( this );
}
/**
* Displays autocomplete popup at the correct location.
*/
private void showAutocompletePopup ()
{
final Point los = AutocompleteField.this.getLocationOnScreen ();
popup.setLocation ( los.x, los.y + getHeight () );
popup.setVisible ( true );
}
/**
* Closes autocomplete popup.
*/
private void hideAutocompletePopup ()
{
popup.setVisible ( false );
}
@Override
public void focusGained ( final FocusEvent e )
{
SwingUtilities.invokeLater ( () -> {
if ( results.size () > 0 )
{
showAutocompletePopup ();
}
} );
}
private void documentChanged ()
{
SwingUtilities.invokeLater ( () -> {
// Updating results list
results.clear ();
results.addAll ( lookup.apply ( getText () ) );
// Updating list view
model.updateView ();
list.setVisibleRowCount ( Math.min ( results.size (), 10 ) );
// Selecting first result
if ( results.size () > 0 )
{
list.setSelectedIndex ( 0 );
}
// Ensure autocomplete popup has correct size
popup.pack ();
// Display or hide popup depending on the results
if ( results.size () > 0 )
{
showAutocompletePopup ();
}
else
{
hideAutocompletePopup ();
}
} );
}
@Override
public void focusLost ( final FocusEvent e )
{
SwingUtilities.invokeLater ( this::hideAutocompletePopup );
}
@Override
public void keyPressed ( final KeyEvent e )
{
if ( e.getKeyCode () == KeyEvent.VK_UP )
{
final int index = list.getSelectedIndex ();
if ( index != -1 && index > 0 )
{
list.setSelectedIndex ( index - 1 );
}
}
else if ( e.getKeyCode () == KeyEvent.VK_DOWN )
{
final int index = list.getSelectedIndex ();
if ( index != -1 && list.getModel ().getSize () > index + 1 )
{
list.setSelectedIndex ( index + 1 );
}
}
else if ( e.getKeyCode () == KeyEvent.VK_ENTER )
{
final String text = ( String ) list.getSelectedValue ();
setText ( text );
setCaretPosition ( text.length () );
}
else if ( e.getKeyCode () == KeyEvent.VK_ESCAPE )
{
hideAutocompletePopup ();
}
}
@Override
public void insertUpdate ( final DocumentEvent e )
{
documentChanged ();
}
@Override
public void removeUpdate ( final DocumentEvent e )
{
documentChanged ();
}
@Override
public void changedUpdate ( final DocumentEvent e )
{
documentChanged ();
}
@Override
public void keyTyped ( final KeyEvent e )
{
// Do nothing
}
@Override
public void keyReleased ( final KeyEvent e )
{
// Do nothing
}
/**
* Custom list model providing data and bridging view update call.
*/
private class ListModel extends AbstractListModel
{
@Override
public int getSize ()
{
return results.size ();
}
@Override
public Object getElementAt ( final int index )
{
return results.get ( index );
}
/**
* Properly updates list view.
*/
public void updateView ()
{
super.fireContentsChanged ( AutocompleteField.this, 0, getSize () );
}
}
/**
* Sample {@link AutocompleteField} usage.
*
* @param args run arguments
*/
public static void main ( final String[] args )
{
final JFrame frame = new JFrame ( "Sample autocomplete field" );
// Sample data list
final List<String> values = Arrays.asList ( "Frame", "Dialog", "Label", "Tree", "Table", "List", "Field" );
// Simple lookup based on our data list
final Function<String, List<String>> lookup = text -> values.stream ()
.filter ( v -> !text.isEmpty () && v.toLowerCase ().contains ( text.toLowerCase () ) && !v.equals ( text ) )
.collect ( Collectors.toList () );
// Autocomplete field itself
final AutocompleteField field = new AutocompleteField ( lookup );
field.setColumns ( 15 );
final JPanel border = new JPanel ( new BorderLayout () );
border.setBorder ( new EmptyBorder ( 50, 50, 50, 50 ) );
border.add ( field );
frame.add ( border );
frame.setDefaultCloseOperation ( WindowConstants.EXIT_ON_CLOSE );
frame.pack ();
frame.setLocationRelativeTo ( null );
frame.setVisible ( true );
}
}
因此，在此示例中，弹出窗口 JWindow 本身未激活（未聚焦）并且无法获得焦点，因为它被强制配置为如此。这使我们能够将注意力集中在JTextField 并继续输入。
在此示例中，我们还捕获字段中的向上/向下箭头等关键事件，以浏览自动完成结果。 ENTER 和 ESCAPE 用于接受/取消结果选择。
此代码也可以稍微重写以使用 Swing PopupFactory 作为自动完成弹出窗口的来源，但本质上仍然是相同的，因为 PopupFactory 使用的 HeavyWeightWindow 只是扩展了 JWindow 和添加了一些设置。