Swing-JList用法-入门

注：本文所有素材均来源于How to Use Lists，本文为该文章的学习笔记。

JList是Swing中的列表控件，形状如下所示：

实际上，JList有3种不同的样式：

分别为HORIZONTAL_WRAP、VERTICAL_WRAP、VERTICAL，通过setLayoutOrientation 进行设置。

构造model

JList每行只有一列，每一列称为一个element。根据MVC架构，其内部的model维护着一个数组，存放了所有的成员元素。因此，对于JList内部元素的处理，都应调用其model的相关方法。

JList共有3种model：

DefaultListModel：对内部成员的操作均已实现，你只需要使用相应的方法即可。

AbstractListModel：手动管理数据并调用相关操作，必须继承AbstractListModel并自己实现其中的getSize和getElementAt方法。

ListModel：手动管理所有事情。

一般来说，我们使用第一种即可。

初始化JList

建议使用DefaultListModel对象作为参数来初始化JList。如果你使用一个数组或vector来初始化JList，或者调用JList.setListData方法来填充它，JList会隐式地生成一个不可修改的默认model，这意味着你无法再对JList进行增删改等操作。

选择元素

JList中的元素选择有三种模式，可通过setSelectionMode来设置：

添加删除元素

调用model的add/remove/insert等方法来实现元素的添加和删除。这里没什么要特别注意的。

定制单元格渲染器

JList使用“单元格渲染器”来显示所有的元素。默认的渲染器只会显示string和图标，对于其它对象，一律调用其toString方法来处理。如果你有特殊的需求，可以使用以下步骤来定制渲染器：

（1）写一个实现了 ListCellRenderer接口的类；

（2）调用setCellRenderer方法，将你的定制渲染器作为参数使用；

Oracle并没有给出Jlist使用定制渲染器的例子，只有一个是关于Combo Box的，其实是一样的啦。Providing a Custom Renderer

选择事件

在《Swing-JList选择事件监听器ListSelectionListener-入门》中专门介绍

数据事件

如果想要对JList中数据的变更进行监听，那么你需要使用addListDataListener添加一个监听器，该监听器必须实现ListDataListener接口。How to Write a List Data Listener进行了详细的介绍并提供了demo。

JListAPI

Demo

下面这个demo包含了JList的常用方法，修改自官网源程序ListDemo.java

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 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */ 

package GUI.components;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

/* ListDemo.java requires no other files. */
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;

    public ListDemo() {
        super(new BorderLayout());

        listModel = new DefaultListModel();
        listModel.addElement("Jane Doe");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");

        //Create the list and put it in a scroll pane.
        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();

        //Create a panel that uses BoxLayout.
        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.SOUTH);
    }

    class FireListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            //This method can be called only if
            //there's a valid selection
            //so go ahead and remove whatever's selected.
            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()) {
                    //removed item in last position
                    index--;
                }

                list.setSelectedIndex(index);
                list.ensureIndexIsVisible(index);
            }
        }
    }

    //This listener is shared by the text field and the hire button.
    class HireListener implements ActionListener, DocumentListener {
        private boolean alreadyEnabled = false;
        private JButton button;

        public HireListener(JButton button) {
            this.button = button;
        }

        //Required by ActionListener.
        public void actionPerformed(ActionEvent e) {
            String name = employeeName.getText();

            //User didn't type in a unique name...
            if (name.equals("") || 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);
            //If we just wanted to add to the end, we'd do this:
            //listModel.addElement(employeeName.getText());

            //Reset the text field.
            employeeName.requestFocusInWindow();
            employeeName.setText("");

            //Select the new item and make it visible.
            list.setSelectedIndex(index);
            list.ensureIndexIsVisible(index);
        }

        //This method tests for string equality. You could certainly
        //get more sophisticated about the algorithm.  For example,
        //you might want to ignore white space and capitalization.
        protected boolean alreadyInList(String name) {
            return listModel.contains(name);
        }

        //Required by DocumentListener.
        public void insertUpdate(DocumentEvent e) {
            enableButton();
        }

        //Required by DocumentListener.
        public void removeUpdate(DocumentEvent e) {
            handleEmptyTextField(e);
        }

        //Required by DocumentListener.
        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;
        }
    }

    //This method is required by ListSelectionListener.
    public void valueChanged(ListSelectionEvent e) {
        if (e.getValueIsAdjusting() == false) {

            if (list.getSelectedIndex() == -1) {
            //No selection, disable fire button.
                fireButton.setEnabled(false);

            } else {
            //Selection, enable the fire button.
                fireButton.setEnabled(true);
            }
        }
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("ListDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        JComponent newContentPane = new ListDemo();
        newContentPane.setOpaque(false); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    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() {
                createAndShowGUI();
            }
        });
    }
}