Java Swing - Jlabel ActionListener 不会打印出选定的复选框

Question

>我有一个JList，它允许你选择要"取消"的选项。单击取消按钮后，JLabel 会打印出哪些选项已被取消。但是，当我尝试测试代码并选择选项并单击"取消"时，JLabel 不会打印任何内容。所以我假设取消按钮的动作监听器不起作用。我在下面包含了相关的代码：

public class WarehouseInterface extends JFrame{
private JFrame frame;
public WarehouseInterface(){
    frame = new JFrame("Warehouse Interface");

    DefaultListModel demoList = new DefaultListModel();
    HashMap<String, Job> jobHashMap = SharedInformation.jobs;
    int i = 0;
    ArrayList<String> jobIDs = new ArrayList<>();
    Iterator it = jobHashMap.entrySet().iterator();
    while (it.hasNext() && i < 10) {
        Map.Entry pair = (Map.Entry)it.next();
        Job job = (Job) pair.getValue();    
        String jobID = job.getID();
        demoList.add(i, jobID);
        jobIDs.add(jobID);
        i++;
    }
    JList list = new JList(demoList);
    list.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
    list.setCellRenderer(new CheckList());
    JButton cancel = new JButton("Cancel");
    cancel.setFont(new Font("Serif", Font.PLAIN, 14));
    JPanel panel2 = new JPanel();
    panel2.setLayout(new GridLayout(2,0));
    panel2.add(list);
    panel2.add(cancel);
    JPanel panel3 = new JPanel();
    panel3.setLayout(new GridLayout(3,0));
    panel3.add(label3);
    ActionListener cancelListener = new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e){
            for(int index : list.getSelectedIndices()) {
                String jobID = (String) demoList.get(index);
                JLabel cancelledJobLabel = new JLabel(jobID);
                cancelledJobLabel.setPreferredSize(new Dimension(50, 20));
                cancelledJobLabel.setFont(new Font("Serif", Font.PLAIN, 18));
                cancelledJobLabel.setOpaque(true);
                panel3.add(cancelledJobLabel);
                //ERROR HERE :(
            }
        }
    };
    cancel.addActionListener(cancelListener);
    frame.add(panel2, BorderLayout.CENTER);
    frame.add(panel3, BorderLayout.SOUTH);
    frame.pack();
    frame.setVisible(true);     

}
    class CheckList extends JLabel implements ListCellRenderer {
        @Override
        public Component getListCellRendererComponent(JList list, Object value, 
                        int index, boolean isSelected, boolean hasFocus) {
            setComponentOrientation(list.getComponentOrientation());
            if (isSelected) {
                 setBackground(Color.RED);
                 setForeground(Color.WHITE);
             // unselected, and not the DnD drop location
             } else {
                 setBackground(Color.WHITE);
                 setForeground(Color.BLACK);
             };
            setOpaque(true);
            setEnabled(list.isEnabled());
            setFont(list.getFont());
            setText(value.toString());
            return this;
        }

    }

Answer 1

panel3.add(cancelledJobLabel);

当您向可见 GUI 添加/删除组件时，基本代码为：

panel.add(...);
panel.revalidate();
panel.repaint();

revalidate()调用布局管理器。否则，组件的大小为 (0， 0(，因此没有要绘制的内容。