在 JList 失去焦点后保持 JList 选择？

Question

我正在尝试使用 JList 和按钮创建一个表单 我想要做的是从 JList 中选择一个项目，然后按下按钮执行依赖于选择的操作。但是，一旦单击按钮，JList 就会失去焦点，选择消失，导致按钮无法确定 JList 中选择了哪个元素。

有解决办法吗？ 在此先感谢:)

Answer 1

只需在每次进行选择时更新一个字段。您可以通过在 JList 上添加侦听器来做到这一点。

private class selectListener extends MouseAdapter {

    public void mouseClicked(MouseEvent e) {
        if (SwingUtilities.isLeftMouseButton(e)) { 
            currentSelected = list.getSelectedIndex();
        }
    }
}

然后在按下按钮时使用该字段。

Answer 2

• 我看不到 Oracle JList 教程中的示例有任何问题

• 看看 ListSelectionListener

• 可能要谨慎使用 SelectionModes

• 你能描述一下你的目标是什么

代码示例

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

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");
        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();
        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.PAGE_END);
    }

    class FireListener implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            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()) {
                    index--;
                }
                list.setSelectedIndex(index);
                list.ensureIndexIsVisible(index);
            }
        }
    }

    class HireListener implements ActionListener, DocumentListener {

        private boolean alreadyEnabled = false;
        private JButton button;

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

        public void actionPerformed(ActionEvent e) {
            String name = employeeName.getText();
            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);
            //listModel.addElement(employeeName.getText());
            employeeName.requestFocusInWindow();
            employeeName.setText("");
            list.setSelectedIndex(index);
            list.ensureIndexIsVisible(index);
        }

        protected boolean alreadyInList(String name) {
            return listModel.contains(name);
        }

        public void insertUpdate(DocumentEvent e) {
            enableButton();
        }

        public void removeUpdate(DocumentEvent e) {
            handleEmptyTextField(e);
        }

        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;
        }
    }

    public void valueChanged(ListSelectionEvent e) {
        if (e.getValueIsAdjusting() == false) {

            if (list.getSelectedIndex() == -1) {
                fireButton.setEnabled(false);
            } else {
                fireButton.setEnabled(true);
            }
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("ListDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JComponent newContentPane = new ListDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                createAndShowGUI();
            }
        });
    }
}