问题描述

关于安卓开发的一个下载问题

//这里是一个片段源代码，下面还有一张出错的日志，希望好心的大神解答一下，这个问题搞了一天还没有结果；
package mars.mp3player.mp3player;

import java.io.StringReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;

import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;

import mars.download.HttpDownloader;
import mars.model.Mp3Info;
import mars.mp3player.service.DownloadService;
import mars.xml.Mp3ListContentHandle;
import android.os.Bundle;
import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class Mp3ListActivity extends ListActivity {

private static final int UPDATE =1;private static final int ABOUT =2;private List<Mp3Info> mp3Infos =null;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.remote_mp3_list);    updateListView();}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {    // Inflate the menu; this adds items to the action bar if it is present.   // getMenuInflater().inflate(R.menu.mp3_list menu);    menu.add(0 UPDATE 1 R.string.mp3list_update);    menu.add(0 ABOUT 2 R.string.mp3list_about);    return super.onCreateOptionsMenu(menu);}@Overridepublic boolean onOptionsItemSelected(MenuItem item) {    // TODO Auto-generated method stub    if (item.getItemId()==UPDATE) {        //用户点击了更新按钮        //下载包含所有MP3 基本信息的xml文件中        System.out.println(""选择的类别""+item.getItemId());    updateListView();//有错误    }    else if (item.getItemId()==ABOUT)    {        //用户点击了关于按钮    }    return super.onOptionsItemSelected(item);}private String downloadXMl(String urlStr){    HttpDownloader httpDownloader = new HttpDownloader();    String result =httpDownloader.download(urlStr);//有错误    return result;}private List<Mp3Info> parse(String xmlStr){   SAXParserFactory saxParserFactory =SAXParserFactory.newInstance();   List<Mp3Info> infos=null;   try {       XMLReader xmlReader =saxParserFactory.newSAXParser().getXMLReader();       infos =new ArrayList<Mp3Info>();       Mp3ListContentHandle mp3ListContentHandle =new Mp3ListContentHandle(infos);       xmlReader.setContentHandler(mp3ListContentHandle);       xmlReader.parse(new InputSource(new StringReader(xmlStr)));       for( Iterator iterator =infos.iterator();iterator.hasNext();)       {           Mp3Info mp3Info =(Mp3Info) iterator.next();           System.out.println(mp3Info);       }} catch (Exception e) {    // TODO: handle exception}    return infos;} private void updateListView(){    String xml =downloadXMl(""http://192.168.191.1:8080/mp3/resources.xml"");//有错误    System.out.println(""xml---->""+xml);//这里没有下载到！    //parse(xml);    //对xMl文件进行解析，并将解的的结果放到MP3info当中的list中去     mp3Infos =parse(xml);    SimpleAdapter simpleAdapter=buildSimpleAdapter(mp3Infos);    setListAdapter(simpleAdapter);} private SimpleAdapter buildSimpleAdapter(List<Mp3Info> mp3Infos){    //生成一个额list对象，并按照simple的标准，将MP3info当中的数据添加的list当中            List<HashMap<String String>> list = new ArrayList<HashMap<StringString>>();            for (Iterator iterator = mp3Infos.iterator();iterator.hasNext();)            {                Mp3Info mp3Info  = (Mp3Info) iterator.next();                HashMap<String String>  map = new HashMap<String String>();                map.put(""mp3_id""mp3Info.getId());                map.put(""mp3_name""mp3Info.getMp3Name());                  list.add(map);            }            //创建一个adapter对象            SimpleAdapter simpleAdapter = new SimpleAdapter(this list R.layout.mp3info_item new String[]{""mp3_id""mp3_name""}new int[]{R.id.mp3_idR.id.mp3_name});            return simpleAdapter;}@Overrideprotected void onListItemClick(ListView l View v int position long id) {    // TODO Auto-generated method stub    Mp3Info mp3Info = mp3Infos.get(position);    Intent intent  = new Intent ();    //将MP3info对象放入intent中    intent.putExtra(""mp3info"" mp3Info);    intent.setClass(this DownloadService.class);    //启动service    startService(intent);    super.onListItemClick(l v position id);}

}

解决方案

http://dampce032.iteye.com/blog/975642
另外检查服务器本身是否有限制

解决方案二：
空指针异常，你看logcat，找到对应的行数
在看什么情况会有空指针
由于你贴出来的代码没有显示行数，我也看不清

解决方案三：
安卓开发问题总结