java – 如何配置JComboBox在创建时不选择FIRST元素？

问题：

更新：

从Java SE 6 API：

public JComboBox() Creates a JComboBox
with a default data model. The default
data model is an empty list of
objects. Use addItem to add items. By
default the first item in the data
model becomes selected.

所以我改为JComboBox(模型),因为API说：

public JComboBox(ComboBoxModel aModel)
Creates a JComboBox that takes its
items from an existing ComboBoxModel.
Since the ComboBoxModel is provided,a
combo Box created using this
constructor does not create a default
combo Box model and may impact how the
insert,remove and add methods behave.

我尝试了以下方法：

DefaultComboBoxModel model = new DefaultComboBoxModel();
    model.setSelectedItem(null);
    suggestionComboBox = new JComboBox(model);
    suggestionComboBox.setModel(model);

但无法让它工作,第一个项目仍然被选中.

任何能够提出工作实例的人都会非常感激.

帖子的老部分：

我正在使用JComboBox,并尝试在我的代码中使用setSelectionIndex(-1)(此代码放在caretInvoke()中)

suggestionComboBox.removeAllItems();
    for (int i = 0; i < suggestions.length; i++) {
        suggestionComboBox.addItem(suggestions[i]);
    }
    suggestionComboBox.setSelectedindex(-1);
    suggestionComboBox.setEnabled(true);

这是添加到窗格时的初始设置：

suggestionComboBox = new JComboBox();
    suggestionComboBox.setEditable(false);
    suggestionComboBox.setPreferredSize(new Dimension(25,25));
    suggestionComboBox.addActionListener(new SuggestionComboBoxListener());

当caretInvoke触发ComboBox初始化时,甚至在用户选择元素之前,actionPerformed已经被触发(我在这里尝试了一个JOptionPane)：
http://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo1.png
http://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo2.png
http://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo3.png

问题是：当用户从ComboBox中选择一个元素时,我的程序会自动插入所选文本.因此,无需用户选择任何内容,它就会自动插入.

在这种情况下如何克服这个问题呢？谢谢.

这是我的SSCCE :(最后)

package components;


import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.JTextArea;
import javax.swing.JTextPane;
import javax.swing.JToolBar;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;
import javax.swing.text.AbstractDocument;
import javax.swing.text.BadLocationException;
import javax.swing.text.StyledDocument;

public class Temp extends JFrame {

    JTextPane textPane;
    AbstractDocument doc;
    JTextArea changeLog;
    String newline = "\n";
    private JComboBox suggestionComboBox;
    private JPanel suggestionPanel;
    private JLabel suggestionLabel;
    private JButton openButton,saveButton,aboutButton;

    public Temp() {
        super("Snort Ruleset IDE");
        //Create the text pane and configure it.
        textPane = new JTextPane();
        textPane.setCaretPosition(0);
        textPane.setMargin(new Insets(5,5,5));
        StyledDocument styledDoc = textPane.getStyledDocument();
        if (styledDoc instanceof AbstractDocument) {
            doc = (AbstractDocument) styledDoc;
            //doc.setDocumentFilter(new DocumentSizefilter(MAX_CHaraCTERS));
        } else {
            System.err.println("Text pane's document isn't an AbstractDocument!");
            System.exit(-1);
        }
        JScrollPane scrollPane = new JScrollPane(textPane);
        scrollPane.setPreferredSize(new Dimension(700,350));

        //Create the text area for the status log and configure it.
        //changeLog = new JTextArea(10,30);
        //changeLog.setEditable(false);
        //JScrollPane scrollPaneForLog = new JScrollPane(changeLog);

        //Create a JPanel for the suggestion area
        suggestionPanel = new JPanel(new BorderLayout());
        suggestionPanel.setVisible(true);
        suggestionLabel = new JLabel("Suggestion is not active at the moment.");
        suggestionLabel.setPreferredSize(new Dimension(100,50));
        suggestionLabel.setMaximumSize(new Dimension(100,50));
        suggestionComboBox = new JComboBox();
        suggestionComboBox.setEditable(false);
        suggestionComboBox.setPreferredSize(new Dimension(25,25));
        //suggestionComboBox.addActionListener(new SuggestionComboBoxListener());
        suggestionComboBox.addItemListener(new SuggestionComboBoxListener());
        //suggestionComboBox.setSelectedindex(-1);

        //add the suggestionLabel and suggestionComboBox to pane
        suggestionPanel.add(suggestionLabel,BorderLayout.CENTER);
        suggestionPanel.add(suggestionComboBox,BorderLayout.PAGE_END);
        JScrollPane sp = new JScrollPane(suggestionPanel);
        JScrollPane scrollPaneForSuggestion = new JScrollPane(suggestionPanel);

        //Create a split pane for the change log and the text area.
        JSplitPane splitPane = new JSplitPane(
                JSplitPane.VERTICAL_SPLIT,scrollPane,scrollPaneForSuggestion);
        splitPane.setonetouchExpandable(true);
        splitPane.setResizeWeight(1.0);
        //disables the moving of divider
        splitPane.setEnabled(false);

        //splitPane.setDividerLocation(splitPane.getHeight());
        //splitPane.setPreferredSize(new Dimension(640,400));

        //Create the status area.
        JPanel statusPane = new JPanel(new GridLayout(1,1));
        CaretListenerLabel caretListenerLabel =
                new CaretListenerLabel("Status: Ready");
        statusPane.add(caretListenerLabel);

        //Create the toolbar
        JToolBar toolBar = new JToolBar();
        toolBar.setFloatable(false);
        toolBar.setRollover(true);

        openButton = new JButton("Open Snort Ruleset");
        toolBar.add(openButton);
        saveButton = new JButton("Save Ruleset");
        toolBar.add(saveButton);
        toolBar.addSeparator();
        aboutButton = new JButton("About");
        toolBar.add(aboutButton);

        //Add the components.
        getContentPane().add(toolBar,BorderLayout.PAGE_START);
        getContentPane().add(splitPane,BorderLayout.CENTER);
        getContentPane().add(statusPane,BorderLayout.PAGE_END);

        JMenu editMenu = createEditMenu();
        JMenu styleMenu = createStyleMenu();
        JMenuBar mb = new JMenuBar();
        mb.add(editMenu);
        mb.add(styleMenu);
        setJMenuBar(mb);


        //Put the initial text into the text pane.
        //initDocument();
        textPane.setCaretPosition(0);

        //Start watching for undoable edits and caret changes.
        textPane.addCaretListener(caretListenerLabel);

        SwingUtilities.invokelater(new Runnable() {

            public void run() {
                textPane.requestFocusInWindow();
            }
        });

    }

    //This listens for and reports caret movements.
    protected class CaretListenerLabel extends JLabel
            implements CaretListener {

        public CaretListenerLabel(String label) {
            super(label);
        }

        //Might not be invoked from the event dispatch thread.
        public void caretUpdate(CaretEvent e) {
            caretInvoke(e.getDot(),e.getMark());
        }

        protected void caretInvoke(final int dot,final int mark) {
            SwingUtilities.invokelater(new Runnable() {

                public void run() {
                    try {
                        Rectangle caretCoords = textPane.modelToView(dot);
                                    //Find suggestion
                                        suggestionComboBox.removeAllItems();
                                        for (int i = 0; i < 5; i++) {
                                            suggestionComboBox.addItem(Integer.toString(i));
                                        }
                                        //suggestionComboBox.setSelectedItem(null);
                                        suggestionComboBox.setEnabled(true);
                                        suggestionLabel.setText("The following keywords are normally used as well. Click to use keyword(s). ");
                                        //changeLog.setText("The following keywords are suggested to be used together: " + str);
                    } catch (BadLocationException ble) {
                        setText("caret: text position: " + dot + newline);
                        System.out.println("Bad Location Exception");
                    }
                }
            });
        }
    }

    public class SuggestionComboBoxListener implements ItemListener {

        //public void actionPerformed(ActionEvent e) {
        public void itemStateChanged(ItemEvent e) {
            if (e.getStateChange() == ItemEvent.SELECTED) {
                JComboBox cb = (JComboBox)e.getSource();
                String selection = (String) cb.getSelectedItem();
                JOptionPane.showMessageDialog(null,"Item is selected","information",JOptionPane.informatION_MESSAGE);
            }
        }
    }

    /*
     * Menu Creation
     */
    //Create the edit menu.
    protected JMenu createEditMenu() {
        JMenu menu = new JMenu("Edit");
        return menu;
    }

    protected JMenu createStyleMenu() {
        JMenu menu = new JMenu("Style");
        return menu;
    }

    private static void createAndShowGUI() {
        //Create and set up the window.
        final Temp frame = new Temp();
        frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeto(null);
        frame.setVisible(true);
    }

    //The standard main method.
    public static void main(String[] args) {
        //Schedule a job for the event dispatch thread:
        //creating and showing this application's GUI.
        SwingUtilities.invokelater(new Runnable() {

            public void run() {
                //Turn off Metal's use of bold fonts
                UIManager.put("swing.boldMetal",Boolean.FALSE);
                createAndShowGUI();
            }
        });
    }
}

解决方法

在对组合框进行任何更改之前,需要删除ItemListener,并在完成后将其添加回来.

像这样的东西：

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Insets;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.SwingUtilities;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;

public class Suggestions {

    private JFrame frame;
    private JTextPane textPane;
    private JComboBox suggestionComboBox;
    private SuggestionComboBoxListener selectionListener;

    public Suggestions() {
        frame = new JFrame("Snort Ruleset IDE");

        textPane = new JTextPane();
        textPane.setCaretPosition(0);
        textPane.setMargin(new Insets(5,5));
        textPane.addCaretListener(new SuggestionCaretListener());
        JScrollPane textEntryScrollPane = new JScrollPane(textPane);
        textEntryScrollPane.setPreferredSize(new Dimension(300,400));

        selectionListener = new SuggestionComboBoxListener(frame);
        suggestionComboBox = new JComboBox();
        suggestionComboBox.setEditable(false);
        suggestionComboBox.setPreferredSize(new Dimension(25,25));
        suggestionComboBox.addItemListener(selectionListener);

        JPanel suggestionPanel = new JPanel(new BorderLayout());
        suggestionPanel.add(suggestionComboBox,BorderLayout.PAGE_END);

        frame.getContentPane().add(textEntryScrollPane,BorderLayout.norTH);
        frame.getContentPane().add(suggestionPanel,BorderLayout.soUTH);
        frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }

    private final class SuggestionCaretListener implements CaretListener {
        @Override
        public void caretUpdate(CaretEvent e) {
            SwingUtilities.invokelater(new Runnable() {
                public void run() {
                    generateSuggestions();
                }
            });
        }
    }

    public static final class SuggestionComboBoxListener implements ItemListener {
        Component parent;
        public SuggestionComboBoxListener(Component parent) {
            this.parent = parent;
        }
        public void itemStateChanged(ItemEvent e) {
            if (e.getStateChange() == ItemEvent.SELECTED) {
                 JComboBox cb = (JComboBox) e.getSource();
                 String selection = (String) cb.getSelectedItem();
                 JOptionPane.showMessageDialog(parent,"The selected item is: " + selection,JOptionPane.informatION_MESSAGE);
            }
        }
    }

    void generateSuggestions() {
        suggestionComboBox.removeItemListener(selectionListener);
        suggestionComboBox.removeAllItems();
        for (int i = 0; i < 5; i++) {
            suggestionComboBox.addItem(Integer.toString(i));
        }
        suggestionComboBox.setEnabled(true);
        suggestionComboBox.addItemListener(selectionListener);
    }

    public static void main(String[] args) {
        new Suggestions();
    }
}

顺便说一下,你发布的不是SSCCE它是你的代码转储. SSCCE应该只有足够的代码来重现您遇到的问题.