如何从 XMLReader 获取属性

我有一些 HTML 正在转换为Spanned using Html.fromHtml(...)，并且我在其中使用了一个自定义标签：

<customtag id="1234">

所以我实现了一个TagHandler处理这个自定义标签，如下所示：

public void handleTag( boolean opening, String tag, Editable output, XMLReader xmlReader ) {

    if ( tag.equalsIgnoreCase( "customtag" ) ) {

        String id = xmlReader.getProperty( "id" ).toString();
    }
}

在这种情况下，我得到一个 SAX 异常，因为我相信“id”字段实际上是一个属性，而不是属性。然而，没有一个getAttribute()方法用于XMLReader。所以我的问题是，如何使用它获取“id”字段的值XMLReader？谢谢。

可以使用XmlReader由...提供TagHandler并无需反射即可访问标签属性值，但该方法比反射更不简单。诀窍是替换ContentHandler被使用过XmlReader与自定义对象。更换ContentHandler只能在调用中完成handleTag()。这就提出了获取第一个标签的属性值的问题，可以通过在 html 开头添加自定义标签来解决这个问题。

import android.text.Editable;
import android.text.Html;
import android.text.Spanned;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

import java.util.ArrayDeque;

public class HtmlParser implements Html.TagHandler, ContentHandler
{
    public interface TagHandler
    {
        boolean handleTag(boolean opening, String tag, Editable output, Attributes attributes);
    }

    public static Spanned buildSpannedText(String html, TagHandler handler)
    {
        // add a tag at the start that is not handled by default,
        // allowing custom tag handler to replace xmlReader contentHandler
        return Html.fromHtml("<inject/>" + html, null, new HtmlParser(handler));
    }

    public static String getValue(Attributes attributes, String name)
    {
        for (int i = 0, n = attributes.getLength(); i < n; i++)
        {
            if (name.equals(attributes.getLocalName(i)))
                return attributes.getValue(i);
        }
        return null;
    }

    private final TagHandler handler;
    private ContentHandler wrapped;
    private Editable text;
    private ArrayDeque<Boolean> tagStatus = new ArrayDeque<>();

    private HtmlParser(TagHandler handler)
    {
        this.handler = handler;
    }

    @Override
    public void handleTag(boolean opening, String tag, Editable output, XMLReader xmlReader)
    {
        if (wrapped == null)
        {
            // record result object
            text = output;

            // record current content handler
            wrapped = xmlReader.getContentHandler();

            // replace content handler with our own that forwards to calls to original when needed
            xmlReader.setContentHandler(this);

            // handle endElement() callback for <inject/> tag
            tagStatus.addLast(Boolean.FALSE);
        }
    }

    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes)
            throws SAXException
    {
        boolean isHandled = handler.handleTag(true, localName, text, attributes);
        tagStatus.addLast(isHandled);
        if (!isHandled)
            wrapped.startElement(uri, localName, qName, attributes);
    }

    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException
    {
        if (!tagStatus.removeLast())
            wrapped.endElement(uri, localName, qName);
        handler.handleTag(false, localName, text, null);
    }

    @Override
    public void setDocumentLocator(Locator locator)
    {
        wrapped.setDocumentLocator(locator);
    }

    @Override
    public void startDocument() throws SAXException
    {
        wrapped.startDocument();
    }

    @Override
    public void endDocument() throws SAXException
    {
        wrapped.endDocument();
    }

    @Override
    public void startPrefixMapping(String prefix, String uri) throws SAXException
    {
        wrapped.startPrefixMapping(prefix, uri);
    }

    @Override
    public void endPrefixMapping(String prefix) throws SAXException
    {
        wrapped.endPrefixMapping(prefix);
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException
    {
        wrapped.characters(ch, start, length);
    }

    @Override
    public void ignorableWhitespace(char[] ch, int start, int length) throws SAXException
    {
        wrapped.ignorableWhitespace(ch, start, length);
    }

    @Override
    public void processingInstruction(String target, String data) throws SAXException
    {
        wrapped.processingInstruction(target, data);
    }

    @Override
    public void skippedEntity(String name) throws SAXException
    {
        wrapped.skippedEntity(name);
    }
}

使用此类读取属性很容易：

    HtmlParser.buildSpannedText("<x id=1 value=a>test<x id=2 value=b>", new HtmlParser.TagHandler()
    {
        @Override
        public boolean handleTag(boolean opening, String tag, Editable output, Attributes attributes)
        {
            if (opening && tag.equals("x"))
            {
                String id = HtmlParser.getValue(attributes, "id");
                String value = HtmlParser.getValue(attributes, "value");
            }
            return false;
        }
    });

这种方法的优点是它允许禁用某些标签的处理，同时对其他标签使用默认处理，例如你可以确保ImageSpan未创建对象：

    Spanned result = HtmlParser.buildSpannedText("<b><img src=nothing>test</b><img src=zilch>",
            new HtmlParser.TagHandler()
            {
                @Override
                public boolean handleTag(boolean opening, String tag, Editable output, Attributes attributes)
                {
                    // return true here to indicate that this tag was handled and
                    // should not be processed further
                    return tag.equals("img");
                }
            });