JList 项目选择

Question

我想知道是否有一种方法，通过使用 JList 选择一个项目，让程序执行一些代码。每次选择新项目时，此代码都应该运行。

之前，我添加了一个侦听器。这是我制作的一个最小示例。

public class Driver {

    public static void main(String[] args) {
        JFrame frame = new ListFrame();
        frame.setVisible(true);
        frame.setSize(200,100);
    }

}

public class ListFrame extends JFrame {

    private JList<String> list; 
    private JScrollPane scrollPane;
    private String[] data = {"A","B","C"};
    private JButton addButton = new JButton("Add");

    public ListFrame() {
        setLayout(new BorderLayout());

        list = new JList<String>(data);
        list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        scrollPane = new JScrollPane(list);

        add(scrollPane, BorderLayout.CENTER);
        add(addButton, BorderLayout.SOUTH);

        addButton.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                String newEntry = JOptionPane.showInputDialog("Add new entry.");
                String[] tempData = new String[data.length + 1];
                for(int i = 0; i < data.length; i++)
                    tempData[i] = data[i];
                tempData[data.length] = newEntry;
                data = tempData;
                list = new JList<String>(data);
                scrollPane.setViewportView(list);
            }

        });

        list.addListSelectionListener(
                new ListSelectionListener() {

                    @Override
                    public void valueChanged(ListSelectionEvent e) {
                        System.out.println("Hi");
                    }

        });
    }
}

但是，当我单击 Jlist 上的项目时，没有打印任何内容。

Answer 1

您的示例使用 getSelectionModel() 获取列表的 ListSelectionModel, and it adds your listener directly to the selection model. This bypasses the ListSelectionHandler, used internally by JList，它永远没有机会 fireSelectionValueChanged()。相反，让 JList 添加您的侦听器：

list.addListSelectionListener(new ListSelectionListener() {...}

when I click an item on the JList, nothing is printed.

当我单击某个项目时，您的新示例会打印 "Hi"，但我发现了一些问题：

一定要运行上event dispatch thread.
查看 ListSelectionEvent 以了解发生的详细信息。
要向列表中添加元素，请不要创建新的JList；改为更新列表的 ListModel。

查看How to Write a List Selection Listener了解更多；这是我测试的例子。

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.ListSelectionModel;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

public class Driver {

    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            JFrame frame = new ListFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setVisible(true);
        });
    }

    private static class ListFrame extends JFrame {

        private final String[] data = {"A", "B", "C"};
        private final DefaultListModel model = new DefaultListModel();
        private final JList<String> list = new JList<>(model);
        private final JButton addButton = new JButton("Add");

        public ListFrame() {
            for (String s : data) {
                model.addElement(s);
            }
            list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
            add(new JScrollPane(list), BorderLayout.CENTER);
            add(addButton, BorderLayout.SOUTH);
            addButton.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent arg0) {
                    String newEntry = JOptionPane.showInputDialog("Add new entry.");
                    model.addElement(newEntry);
                }
            });
            list.addListSelectionListener(new ListSelectionListener() {

                @Override
                public void valueChanged(ListSelectionEvent e) {
                    if (!e.getValueIsAdjusting()) {
                        System.out.println(e.getFirstIndex() + " " + e.getLastIndex());
                    }
                }
            });
        }
    }
}

JList 项目选择

JList Item Selection

java

swing

jlist

listselectionlistener