Question

我有JList，在某些面板层次结构中，我无法通过键 UP 和 DOWN 事件更改选择，并注意到我不要向我的JList发送任何关键事件，因此我开始通过添加以下行来调查Swing层次结构的焦点管理：

mJList.addFocusListener(new FocusListener() {

    @Override
    public void focusLost(FocusEvent e) {
        System.out.println("focusLost to "+e.getOppositeComponent());
        //mJList.requestFocus();
    }

    @Override
    public void focusGained(FocusEvent e) {
        System.out.println("focusGained");
    }
});

一开始，我注意到我的一些按钮在我JList获得它后几毫秒获得了焦点，所以我让所有这些按钮都不可聚焦，然后我得到了这个奇怪的结果，我的{{1失去焦点...... null ？！？！

JList

然后我添加了在focusLost方法中注释掉的行，以便在丢失时重新获得焦点，但我认为这是一个非常糟糕的长期解决方案，所以我的问题是：

为什么我的focusGained focusLost to null仅获得时间焦点，如果不是这样，那为什么会被迫放弃JList？
如何以正确的（良好实践）方式解决问题？

Answer 1

请您在此SSCCE上解释您的问题，否则发布您自己的

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

public class Testing extends JFrame {

    private static final long serialVersionUID = 1L;
    private DefaultListModel listModel = new DefaultListModel();
    private JList list = new JList(listModel);
    private JScrollPane sp = new JScrollPane(list);
    private JButton btn1 = new JButton("Reset Model with freeze");
    private JButton btn2 = new JButton("Reset Model with change selection");
    private int xX = 0;

    public Testing() {
        for (int x = 0; x < 19; x++) {
            listModel.addElement("" + x);
            xX++;
        }
        btn1.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                listModel.removeAllElements();
                // caused locking GUI for long time in the case 
                // that Item count is more than 999 Items
                for (int x = 0; x < 19; x++) {
                    listModel.addElement("" + (x + xX));
                    xX++;
                }
            }
        });
        btn2.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent ae) {
                //list.clearSelection();
                if (list.getSelectedIndex() == 0) {
                    list.setSelectedIndex(1);
                }
                listModel.removeAllElements();
                for (int x = 0; x < 19; x++) {
                    listModel.addElement("" + (x + xX));
                    xX++;
                }
                list.setSelectedIndex(0);
            }
        });
        add(sp, BorderLayout.CENTER);
        add(btn1, BorderLayout.NORTH);
        add(btn2, BorderLayout.SOUTH);
        setLocation(400, 300);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        pack();
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                list.setSelectedIndex(0);
            }
        });
        list.addFocusListener(new FocusListener() {
            @Override
            public void focusLost(FocusEvent e) {
                System.out.println("focusLost to " + e.getOppositeComponent());
                //mJList.requestFocus();
            }

            @Override
            public void focusGained(FocusEvent e) {
                System.out.println("focusGained");
            }
        });
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Testing().setVisible(true);
            }
        });
    }
}

为什么我的JList获得临时焦点？

1 个答案: