java - 将XML解析为TextView : android

Question

我正在开发一个在 Android 中显示图书列表的应用程序。我从服务器检索 XML 文件并将内容解析为相应的 TextView。

我的 XML 文件:

<bib>
<book year="1988">
    <title>Book Title</title>
    <author>
        <last>Jones</last>
        <first>Ryan</first>
    </author>
</book>

<book year="2001">
    <title>Book Title 2</title>
    <author>
        <last>Ryans</last>
        <first>Jack</first>
    </author>
</book>

我正在使用 ViewModel 通过 NodeList 将 XML 解析到我的应用程序中。

ViewModel.java:

try {

                String bFeed = getApplication().getString(R.string.feed);

                URL url = new URL(bFeed);
                URLConnection connection = url.openConnection();
                HttpURLConnection httpConnection = (HttpURLConnection) connection;
                int responseCode = httpConnection.getResponseCode();

                if (responseCode == HttpURLConnection.HTTP_OK) {

                    InputStream in = httpConnection.getInputStream();
                    DocumentBuilderFactory dbf =
                            DocumentBuilderFactory.newInstance();
                    DocumentBuilder db = dbf.newDocumentBuilder();

                    // Parse the book feed.
                    Document dom = db.parse(in);
                    // Returns the root element.
                    Element docEle = dom.getDocumentElement();
                    books.clear();

                    NodeList nl = docEle.getElementsByTagName("book");
                    if (nl != null && nl.getLength() > 0) {

                        for (int i = 0; i < nl.getLength(); i++) {

                            if (isCancelled()) {
                                return books;
                            }
                            Element bookElement = (Element) nl.item(i);
                            Element title = (Element) bookElement
                                    .getElementsByTagName("title").item(0);
                            Element author = (Element) bookElement
                                    .getElementsByTagName("author").item(0);

                            String bookTitle = title.getFirstChild().getNodeValue();
                            String bookYear = ((Element) bookElement).getAttribute("year");
                            // Error occurs
                            String bookAuthor = author.getFirstChild().getNodeValue();

                            final Book bookObject = new Book(bookTitle, bookYear, bookAuthor);
                            books.add(bookObject);

                        }
                    }
                }
                httpConnection.disconnect();
            } catch (MalformedURLException e) {
                Log.e(TAG, "MalformedURLException", e);
            } catch (IOException e) {
                Log.e(TAG, "IOException", e);
            } catch (ParserConfigurationException e) {
                Log.e(TAG, "Parser Configuration Exception", e);
            } catch (SAXException e) {
                Log.e(TAG, "SAX Exception", e);
            }

            return books;
        }

我在运行时遇到此错误:

原因:java.lang.NullPointerException:尝试在空对象引用上调用接口(interface)方法“org.w3c.dom.Node org.w3c.dom.Element.getFirstChild()”

书.java:

public class Book {
private String year;
private String title;
private String author;


public String getYear() { return year; }

public String getTitle() {
    return title;
}

public String getAuthor() { return author; }

public Book(String year, String title, String author) {

    this.year = year;
    this.title = title;
    this.author = author;

}

我希望能够获取作者的子节点。如果有人能就我做错了什么提供任何建议，我将不胜感激？

谢谢

Answer 1

您收到的错误非常清楚:

java.lang.NullPointerException: Attempt to invoke interface method 'org.w3c.dom.Node org.w3c.dom.Element.getFirstChild()' on a null object reference

意思是，您试图在一个空对象上调用 getFirstChildMethod。

我会在下面的行中检查:

String bookTitle = title.getFirstChild().getNodeValue();

标题确实有值(value)。

如果没有看到您正在解析的实际 XML，这些行就是罪魁祸首:

Element bookElement = (Element) nl.item(i);
Element title = (Element) bookElement.getElementsByTagName("title").item(0);