Java 如何配置 JComboBox 在创建时不选择第一个元素？

How to configure JComboBox not to select FIRST element when created?

提问by Alex Cheng

Problem:

问题：

Update:

更新：

From the Java SE 6 API:

来自 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.

public JComboBox()创建一个带有默认数据模型的 JComboBox。默认数据模型是一个空的对象列表。使用 addItem 添加项目。默认情况下，数据模型中的第一项被选中。

So I changed to JComboBox(model) as the API says:

所以我改成 JComboBox(model) 就像 API 说的：

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 modeland may impact how the insert, remove and add methods behave.

public JComboBox(ComboBoxModel aModel)创建一个 JComboBox，它从现有的 ComboBoxModel 中获取其项目。由于提供了 ComboBoxModel，因此使用此构造函数创建的组合框不会创建默认组合框模型，并且可能会影响插入、删除和添加方法的行为方式。

I tried the following:

我尝试了以下方法：

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

But could not get it to work, the first item is still being selected.

但无法让它工作，第一项仍在被选中。

Anyone that can come up with a working example would be very much appreciated.

任何能想出一个工作示例的人都会非常感激。

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Old part of the post:

帖子的旧部分：

I am using JComboBox, and tried using setSelectionIndex(-1)in my code (this code is placed in caretInvoke())

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

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

This is the initial setting when it was added to a pane:

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());

When the caretInvoke triggers the ComboBox initialisation, even before the user selects an element, the actionPerformed is already triggered (I tried a JOptionPane here): http://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo1.pnghttp://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo2.pnghttp://i126.photobucket.com/albums/p109/eXPeri3nc3/StackOverflow/combo3.png

当 caretInvoke 触发 ComboBox 初始化时，甚至在用户选择一个元素之前，actionPerformed 就已经被触发（我在这里尝试了 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

The problem is: My program autoinserts the selected text when the user selects an element from the ComboBox. So without the user selecting anything, it is automatically inserted already.

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选定的文本。因此，无需用户选择任何内容，它就会自动插入。

How can I overcome the problem in this situation? Thanks.

在这种情况下，我该如何克服这个问题？谢谢。

Here is my SSCCE: (finally)

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, 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();
            }
        });
    }
}

采纳答案by Goibniu

You need to remove the ItemListener before you make any changes to the combo-box and add it back when you are done.

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

Something like this:

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, 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, "Information",
                 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();
    }
}

BTW, what you posted is not an SSCCE it is a dump of your code. An SSCCE should only have enough code to reproduce the issue you are experiencing.

顺便说一句，您发布的内容不是 SSCCE，而是您代码的转储。SSCCE 应该只有足够的代码来重现您遇到的问题。

回答by sreejith

use

用

setSelectedItem(null);

Please try with ItemListener instead of ActionListener.

请尝试使用 ItemListener 而不是 ActionListener。

回答by Mohsin

if You want that after 1st entry you made and immediately you combox is empty then just write down the under mentioned code which is:

如果你想在你第一次输入后立即你的组合框是空的，那么只需写下下面提到的代码：

jComboBox1.setSelectedIndex(0);   

and your combox will reset Automatically

并且您的组合框将自动重置