java - 将 XML 解析值添加到 JList 中不起作用

Question

我已经解析了一个 XML 文件，其中包含一些我想在 JList 中显示的元素。解析工作正常，但在 Jlist 中显示它根本不起作用。

我已尝试执行以下操作:

1. 解析 XML。
2. 将节点添加到 DefaultModelList。
3. 将模型添加到Jlist。

我的代码:

public class ReadXMLFile {

    private DefaultListModel model = new DefaultListModel();

    private static ReadXMLFile instance = null;

    public static ReadXMLFile getInstance() {

        if (instance == null) {

            instance = new ReadXMLFile();

        }

        return instance;
    }

    public void ParserForObjectTypes() throws SAXException, IOException,
            ParserConfigurationException {

        try {
            FileInputStream file = new FileInputStream(new File(
                    "xmlFiles/CoreDatamodel.xml"));

            DocumentBuilderFactory builderFactory = DocumentBuilderFactory
                    .newInstance();

            DocumentBuilder builder = builderFactory.newDocumentBuilder();

            Document xmlDocument = builder.parse(file);

            XPath xPath = XPathFactory.newInstance().newXPath();

            String expression = "//OBJECT_TYPE";
            NodeList nodeList = (NodeList) xPath.compile(expression).evaluate(
                    xmlDocument, XPathConstants.NODESET);
            for (int i = 0; i < nodeList.getLength(); i++) {

                model.addElement(nodeList.item(i).getFirstChild()
                        .getNodeValue());
                System.out.println(nodeList.item(i).getFirstChild()
                        .getNodeValue());
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
    }

    public DefaultListModel getModel() {
        return model;
    }

}

然后在我的 GUI 构造函数中调用我的 initialize 方法，它将我的模型放入 JList。 initialize() 的重要部分如下所示:

private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 823, 515);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JList obTypeJList = new JList(ReadXMLFile.getInstance().getModel());
    JMenuBar menuBar = new JMenuBar();
        frame.setJMenuBar(menuBar);

        JMenu contentMenuBar = new JMenu("File");
        menuBar.add(contentMenuBar);

        JMenuItem OpenFileItemMenu = new JMenuItem("Open File");
        contentMenuBar.add(OpenFileItemMenu);

    }


public XmlEditorMain() {
    initialize();
    ReadXMLFile file = new ReadXMLFile();
    try {
        file.ParserForObjectTypes();
    } catch (SAXException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ParserConfigurationException e) {
        e.printStackTrace();
    }
}

Answer 1

您正在创建单例实例，但您忘记了初始化它。变化:

public static ReadXMLFile getInstance() {
       if (instance == null) {
            instance = new ReadXMLFile();
        }
        return instance;
    }

到

public static ReadXMLFile getInstance() {
       if (instance == null) {
            instance = new ReadXMLFile();
            instance.ParserForObjectTypes();
        }
        return instance;
    }