java - 异常似乎终止了 JList 的更新

Question

每当选择一个项目时，我都会使用 ActionListener 更新 JList。

jComboBox.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        JComboBox cb = (JComboBox) e.getSource();
        updateLocalFileList( cb.getSelectedItem().toString() );
    }
});

它正在为 UI 调用此方法。

public void updateLocalFileList( String path ){
    DefaultListModel model = new DefaultListModel();
    for (String str : LocalFileSystem.getFileListFromDirectory( path )) {
        model.addElement( str );
    }
    getJList().setModel(model);
}

如果 getFileListFromDirectory() 给出 NullPointerException，例如选择空 DVD 驱动器的盘符时，它似乎会阻止 ActionListener 按预期工作。

我不确定到底发生了什么，但我怀疑向模型传递空值导致了此问题。

有什么想法吗？

编辑

这是所请求的堆栈跟踪。正如您所看到的，该方法显然在无法访问的驱动器上触发了 NullPointerException。我不明白为什么它会阻止 JList 更新，因为应用程序的其余部分工作正常。

java.lang.NullPointerException
    at mine.View.updateLocalFileList(View.java:274)
    at mine.View$1.actionPerformed(View.java:262)
    at javax.swing.JComboBox.fireActionEvent(Unknown Source)
    at javax.swing.JComboBox.setSelectedItem(Unknown Source)
    at javax.swing.JComboBox.setSelectedIndex(Unknown Source)
    at javax.swing.plaf.basic.BasicComboPopup$Handler.mouseReleased(Unknown Source)
    at java.awt.AWTEventMulticaster.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at javax.swing.plaf.basic.BasicComboPopup$1.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

我会做两件事来使其更加稳健。

1. 确保 getFileListFromDirectory 永远不会返回 null。如果没有项目，则返回 Collections.emptyList 而不是 null。如果这是不可能的，请在使用“foreach”迭代之前专门检查返回值。此时，空指针将阻止模型更新。 (因此单击空驱动器不会清除文件列表。)
2. 将 cb.getSelectedItem() 分配给局部变量并在调用 updateLocalFileList 之前检查是否为 null。如果cb.getSelectedItem()为null，您可以选择清除文件列表。