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我正在尝试为 Android 制作一个 SAX 解析器，并从外部 XML 文件中仅读取一个标签开始。我收到“不幸的是，-- 已停止”错误。我查看了日志文件，它给了我一个空引用错误。我的猜测是 XMLAdapter 类不能正常工作，我无法解决问题。

这是我的主要活动：

package com.vint.michiganbus;

import java.net.URL;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.view.Window;
import android.util.Log;


public class listView extends Activity {
    XMLGettersSetters data;
    private static final String TAG = "listView";
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        View layout = findViewById(R.id.layout);

        TextView title[];

        Log.i(TAG, "data is hello");
        try {
            /**
            * Create a new instance of the SAX parser
            **/
            SAXParserFactory saxPF = SAXParserFactory.newInstance();
            SAXParser saxP = saxPF.newSAXParser();
            XMLReader xmlR = saxP.getXMLReader();

            URL url = new URL("http://mbus.pts.umich.edu/shared/public_feed.xml"); // URL of the XML

            /**
            * Create the Handler to handle each of the XML tags.
            **/
            XMLHandler myXMLHandler = new XMLHandler();
            xmlR.setContentHandler(myXMLHandler);
            xmlR.parse(new InputSource(url.openStream()));

        } catch (Exception e) {
            System.out.println(e);
        }

        data = XMLHandler.data;

        /** 
         * Makes the TextView length the size of the TextView arrays by getting the size of the 
         **/
        title = new TextView[data.get().size()];        

        /** 
         * Run a for loop to set All the TextViews with text until 
         * the size of the array is reached.
         * 
         **/
        for (int i = 0; i < data.get().size(); i++) {

            title[i] = new TextView(this);
            title[i].setText("Title = "+data.get().get(i));

            ((ViewGroup) layout).addView(title[i]);
            }

        setContentView(layout);

        //setContentView(R.layout.listview);
    }
}

这是我的 XML 处理程序：

package com.vint.michiganbus;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import android.util.Log;

public class XMLHandler extends DefaultHandler {
    private static final String TAG = "In Handler";
    String elementValue = null;
    Boolean elementOn = false;
    public static XMLGettersSetters data = null;

    public static XMLGettersSetters getXMLData() {
        return data;
    }

    public static void setXMLData(XMLGettersSetters data) {
        XMLHandler.data = data;
    }

    /**
     * This will be called when the tags of the XML starts.
     **/
    @Override
    public void startElement(String uri, String localName, String qName,
            Attributes attributes) throws SAXException {

        elementOn = true;
        Log.i(TAG, "starting Element "+localName);
        if (localName.equals("livefeed"))
        {
            data = new XMLGettersSetters();
        } else if (localName.equals("routecount")) {
            /**
             * We can get the values of attributes for eg. if the CD tag had an attribute( <CD attr= "band">Akon</CD> )
             * we can get the value "band". Below is an example of how to achieve this.
             *
             * String attributeValue = attributes.getValue("attr");
             * data.setAttribute(attributeValue);
             *
             * */
        }
    }

    /**
     * This will be called when the tags of the XML end.
     **/
    @Override
    public void endElement(String uri, String localName, String qName)
            throws SAXException {

        elementOn = false;

        /**
         * Sets the values after retrieving the values from the XML tags
         * */
        if (localName.equalsIgnoreCase("routecount"))
            data.set(elementValue);
        /*else if (localName.equalsIgnoreCae("artist"))
            data.setArtist(elementValue);
        else if (localName.equalsIgnoreCase("country"))
            data.setCountry(elementValue);
        else if (localName.equalsIgnoreCase("company"))
            data.setCompany(elementValue);
        else if (localName.equalsIgnoreCase("price"))
            data.setPrice(elementValue);
        else if (localName.equalsIgnoreCase("year"))
            data.setYear(elementValue);*/
    }

    /**
     * This is called to get the tags value
     **/
    @Override
    public void characters(char[] ch, int start, int length)
            throws SAXException {

        if (elementOn) {
            elementValue = new String(ch, start, length);
            elementOn = false;
        }

    }

}

这是我的 GetterSetter 类

package com.vint.michiganbus;

import java.util.ArrayList;

public class XMLGettersSetters {
    private ArrayList<String> routecount = new ArrayList<String>();

    public ArrayList<String> get() {
        return routecount;
    }
    public void set(String company) {
            this.routecount.add(company);
    }
}

任何帮助将不胜感激！

ps：如果有人对如何有效地处理 URL 中的 XML 有任何建议，我会很高兴的！

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1 回答 1

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错误可能是您正尝试从活动线程中检索 Web 文件。我将创建一个 AsyncTask，将我所有的解析器代码放在 AsyncTask 的 doInBackground() 方法中。看起来像这样的东西：

private class DownloadFilesTask extends AsyncTask<Document, Integer, Document> 
{
    Document doc;
    String xml;

    public DownloadFilesTask(){}

    protected Document doInBackground(Document... params) 
    {
        xml = xmlFunctions.getXML("Your URL");
        doc = XmlFunctions.XMLfromString(xml);
        return doc;
    } 
    protected void onPostExecute(Document result) 
    {
      //Some code changing UI from the nodes you've just parsed
    }  
}

然后你可以在你的 onCreate 中调用这个类：

new DownloadTaskfiles().execute();

希望这个对你有帮助！

于 2012-06-06T13:15:11.320 回答