[轉貼] android 多线程断点续传下载

文章來源 : android 多线程断点续传下载

今天跟大家一起分享下android开发中比较难的一个环节,可能很多人看到这个标题就会感觉头很大,的确如果没有良好的编码能力和逻辑思维,这块是很难搞明白的,前面2次总结中已经为大家分享过有关技术的一些基本要领,我们先一起简单回顾下它的基本原理。

http://blog.csdn.net/shimiso/article/details/6763664  android 多线程断点续传下载 一

http://blog.csdn.net/shimiso/article/details/6763986  android 多线程断点续传下载 二

什么是多线程下载？

多线程下载其实就是迅雷,BT一些下载原理,通过多个线程同时和服务器连接,那么你就可以榨取到较高的带宽了,大致做法是将文件切割成N块,每块交给单独一个线程去下载,各自下载完成后将文件块组合成一个文件,程序上要完成做切割和组装的小算法

什么是断点续传?

断点续传,就是当我们下载未结束时候,退出保存下载进度,当下次打开继续下载的时接着上次的进度继续下载,不用每次下载都重新开始,那么有关断点续传的原理和实现手段,可参考我以前的一篇总结http://blog.csdn.net/shimiso/article/details/5956314 里面详细讲解http协议断点续传的原理,务必要看懂,否则你无法真正理解本节代码

怎么完成多线程断点续传?

将两者合二为一需要程序记住每个文件块的下载进度,并保存入库,当下载程序启动时候你需要判断程序是否已经下载过该文件,并取出各个文件块的保存记录,换算出下载进度继续下载,在这里你需要掌握java多线程的基本知识,handler的使用,以及集合,算法,文件操作等基本技能,同时还要解决sqlite数据库的同步问题,因为它是不太怎么支持多线程操作的,控制不好经常会出现库被锁定的异常,同时在android2.3以后就不能activity中直接操作http,否则你将收到系统送上的NetworkOnMainThreadException异常,在UI体验上一定记住要使用异步完成,既然大致思路已经清楚,下面我们开始分析程序:

package cn.demo.DBHelper;
 
 import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
 
     /**
      * 建立一个数据库帮助类
      */
 public class DBHelper extends SQLiteOpenHelper {
     //download.db-->数据库名
     public DBHelper(Context context) {
         super(context, "download.db", null, 1);
     }
     
     /**
      * 在download.db数据库下创建一个download_info表存储下载信息
      */
     @Override
     public void onCreate(SQLiteDatabase db) {
         db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "
                 + "start_pos integer, end_pos integer, compelete_size integer,url char)");
     }
     @Override
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 
     }
 
 }

 数据库操作要借助单例和同步,来保证线程的执行顺序,以免多个线程争相抢用sqlite资源导致异常出现

package cn.demo.Dao;

import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.demo.DBHelper.DBHelper;
import cn.demo.entity.DownloadInfo;

/**
 * 
 * 一个业务类
 */
public class Dao {  
 private static Dao dao=null;
 private Context context; 
 private  Dao(Context context) { 
  this.context=context;
 }
 public static  Dao getInstance(Context context){
  if(dao==null){
   dao=new Dao(context); 
  }
  return dao;
 }
 public  SQLiteDatabase getConnection() {
  SQLiteDatabase sqliteDatabase = null;
  try { 
   sqliteDatabase= new DBHelper(context).getReadableDatabase();
  } catch (Exception e) {  
  }
  return sqliteDatabase;
 }

 /**
  * 查看数据库中是否有数据
  */
 public synchronized boolean isHasInfors(String urlstr) {
  SQLiteDatabase database = getConnection();
  int count = -1;
  Cursor cursor = null;
  try {
   String sql = "select count(*)  from download_info where url=?";
   cursor = database.rawQuery(sql, new String[] { urlstr });
   if (cursor.moveToFirst()) {
    count = cursor.getInt(0);
   } 
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != database) {
    database.close();
   }
   if (null != cursor) {
    cursor.close();
   }
  }
  return count == 0;
 }

 /**
  * 保存 下载的具体信息
  */
 public synchronized void saveInfos(List<DownloadInfo> infos) {
  SQLiteDatabase database = getConnection();
  try {
   for (DownloadInfo info : infos) {
    String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";
    Object[] bindArgs = { info.getThreadId(), info.getStartPos(),
      info.getEndPos(), info.getCompeleteSize(),
      info.getUrl() };
    database.execSQL(sql, bindArgs);
   }
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != database) {
    database.close();
   }
  }
 }

 /**
  * 得到下载具体信息
  */
 public synchronized List<DownloadInfo> getInfos(String urlstr) {
  List<DownloadInfo> list = new ArrayList<DownloadInfo>();
  SQLiteDatabase database = getConnection();
  Cursor cursor = null;
  try {
   String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
   cursor = database.rawQuery(sql, new String[] { urlstr });
   while (cursor.moveToNext()) {
    DownloadInfo info = new DownloadInfo(cursor.getInt(0),
      cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),
      cursor.getString(4));
    list.add(info);
   }
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != database) {
    database.close();
   }
   if (null != cursor) {
    cursor.close();
   }
  }
  return list;
 }

 /**
  * 更新数据库中的下载信息
  */
 public synchronized void updataInfos(int threadId, int compeleteSize, String urlstr) {
  SQLiteDatabase database = getConnection();
  try {
   String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
   Object[] bindArgs = { compeleteSize, threadId, urlstr };
   database.execSQL(sql, bindArgs);
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != database) {
    database.close();
   }
  }
 }

 /**
  * 下载完成后删除数据库中的数据
  */
 public synchronized void delete(String url) {
  SQLiteDatabase database = getConnection();
  try {
   database.delete("download_info", "url=?", new String[] { url });
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != database) {
    database.close();
   }
  }
 }
}

package cn.demo.download;

import java.util.List;
import java.util.Map;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.TextView;




public class DownLoadAdapter extends BaseAdapter{
  
 private LayoutInflater mInflater;
 private List<Map<String, String>> data;
 private Context context;
 private OnClickListener click;
 
 public DownLoadAdapter(Context context,List<Map<String, String>> data) {
  this.context=context;
  mInflater = LayoutInflater.from(context);
  this.data=data;
 }
 public void refresh(List<Map<String, String>> data) {
  this.data=data;
  this.notifyDataSetChanged();
 }
 public void setOnclick(OnClickListener click) {
   this.click=click;
 }
 
 
 @Override
 public int getCount() {
  return data.size();
 }

 @Override
 public Object getItem(int position) {
  return data.get(position);
 }

 @Override
 public long getItemId(int position) {
  return position;
 }

 @Override
 public View getView(final int position, View convertView, ViewGroup parent) {
  final Map<String, String> bean=data.get(position);
  ViewHolder holder = null;
  if (convertView == null) {
   convertView = mInflater.inflate(R.layout.list_item, null);
   holder = new ViewHolder(); 
   holder.resouceName=(TextView) convertView.findViewById(R.id.tv_resouce_name);
   holder.startDownload=(Button) convertView.findViewById(R.id.btn_start);
   holder.pauseDownload=(Button) convertView.findViewById(R.id.btn_pause);
   convertView.setTag(holder);
  } else {
   holder = (ViewHolder) convertView.getTag();
  } 
   holder.resouceName.setText(bean.get("name")); 
  return convertView;
 }
 public OnClickListener getClick() {
  return click;
 }
 public void setClick(OnClickListener click) {
  this.click = click;
 }
 private class ViewHolder { 
        public TextView resouceName;
        public Button startDownload;
        public Button pauseDownload;
      
        
     
    }
 
}

注意子线程不要影响主UI线程,灵活运用task和handler,各取所长,保证用户体验,handler通常在主线程中有利于专门负责处理UI的一些工作

package cn.demo.download;
 
 import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.app.ListActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import android.widget.ProgressBar; 
import android.widget.TextView;
import android.widget.Toast;
import cn.demo.entity.LoadInfo;
import cn.demo.service.Downloader;

 public class MainActivity extends ListActivity { 
     // 固定下载的资源路径，这里可以设置网络上的地址
     private static final String URL = "http://download.haozip.com/";
     // 固定存放下载的音乐的路径：SD卡目录下
     private static final String SD_PATH = "/mnt/sdcard/";
     // 存放各个下载器
     private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
     // 存放与下载器对应的进度条
     private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
     /**
      * 利用消息处理机制适时更新进度条
      */
     private Handler mHandler = new Handler() {
         public void handleMessage(Message msg) {
             if (msg.what == 1) {
                 String url = (String) msg.obj;
                 int length = msg.arg1;
                 ProgressBar bar = ProgressBars.get(url);
                 if (bar != null) {
                     // 设置进度条按读取的length长度更新
                     bar.incrementProgressBy(length);
                     if (bar.getProgress() == bar.getMax()) {
                      LinearLayout layout = (LinearLayout) bar.getParent();
                      TextView resouceName=(TextView)layout.findViewById(R.id.tv_resouce_name);
                         Toast.makeText(MainActivity.this, "["+resouceName.getText()+"]下载完成！", Toast.LENGTH_SHORT).show();
                         // 下载完成后清除进度条并将map中的数据清空
                         layout.removeView(bar);
                         ProgressBars.remove(url);
                         downloaders.get(url).delete(url);
                         downloaders.get(url).reset();
                         downloaders.remove(url);
                         
                         Button btn_start=(Button)layout.findViewById(R.id.btn_start);
                         Button btn_pause=(Button)layout.findViewById(R.id.btn_pause);
                         btn_pause.setVisibility(View.GONE);
                         btn_start.setVisibility(View.GONE);
                     }
                 }
             }
         }
     };
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main); 
         showListView();
     }
     // 显示listView，这里可以随便添加
     private void showListView() {
         List<Map<String, String>> data = new ArrayList<Map<String, String>>();
         Map<String, String> map = new HashMap<String, String>();
         map.put("name", "haozip_v3.1.exe");
         data.add(map);
         map = new HashMap<String, String>();
         map.put("name", "haozip_v3.1_hj.exe");
         data.add(map);
         map = new HashMap<String, String>();
         map.put("name", "haozip_v2.8_x64_tiny.exe");
         data.add(map);
         map = new HashMap<String, String>();
         map.put("name", "haozip_v2.8_tiny.exe");
         data.add(map);
         DownLoadAdapter adapter=new DownLoadAdapter(this,data);  
         setListAdapter(adapter);
         
     }
     /**
      * 响应开始下载按钮的点击事件
      */
     public void startDownload(View v) {
         // 得到textView的内容 
         LinearLayout layout = (LinearLayout) v.getParent();
         String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
         String urlstr = URL + resouceName;
         String localfile = SD_PATH + resouceName;
         //设置下载线程数为4，这里是我为了方便随便固定的
         String threadcount = "4";
         DownloadTask downloadTask=new DownloadTask(v);
         downloadTask.execute(urlstr,localfile,threadcount);
       
     };
    class DownloadTask extends AsyncTask<String, Integer, LoadInfo>{
     Downloader downloader=null; 
     View v=null;
     String urlstr=null;
     public DownloadTask(final View v){
      this.v=v;
     }  
     @Override
     protected void onPreExecute() { 
      Button btn_start=(Button)((View)v.getParent()).findViewById(R.id.btn_start);
      Button btn_pause=(Button)((View)v.getParent()).findViewById(R.id.btn_pause);
      btn_start.setVisibility(View.GONE);
      btn_pause.setVisibility(View.VISIBLE);
     }
  @Override
  protected LoadInfo doInBackground(String... params) {
   urlstr=params[0];
   String localfile=params[1];
   int threadcount=Integer.parseInt(params[2]);
    // 初始化一个downloader下载器
          downloader = downloaders.get(urlstr);
          if (downloader == null) {
              downloader = new Downloader(urlstr, localfile, threadcount, MainActivity.this, mHandler);
              downloaders.put(urlstr, downloader);
          }
          if (downloader.isdownloading())
           return null;
          // 得到下载信息类的个数组成集合
          return downloader.getDownloaderInfors(); 
  }
  @Override
  protected void onPostExecute(LoadInfo loadInfo) {
   if(loadInfo!=null){
     // 显示进度条
           showProgress(loadInfo, urlstr, v);
           // 调用方法开始下载
           downloader.download();
   } 
  }
   
  };
     /**
      * 显示进度条
      */
     private void showProgress(LoadInfo loadInfo, String url, View v) {
         ProgressBar bar = ProgressBars.get(url);
         if (bar == null) {
             bar = new ProgressBar(this, null, android.R.attr.progressBarStyleHorizontal);
             bar.setMax(loadInfo.getFileSize());
             bar.setProgress(loadInfo.getComplete());
             ProgressBars.put(url, bar);
             LinearLayout.LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, 5);
             ((LinearLayout) ((LinearLayout) v.getParent()).getParent()).addView(bar, params);
         }
     }
     /**
      * 响应暂停下载按钮的点击事件
      */
     public void pauseDownload(View v) {
         LinearLayout layout = (LinearLayout) v.getParent();
         String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
         String urlstr = URL + resouceName;
         downloaders.get(urlstr).pause();
         Button btn_start=(Button)((View)v.getParent()).findViewById(R.id.btn_start);
    Button btn_pause=(Button)((View)v.getParent()).findViewById(R.id.btn_pause);
         btn_pause.setVisibility(View.GONE);
         btn_start.setVisibility(View.VISIBLE);
     }
 }

 这是一个信息的实体,记录了一些字典信息,可以认为是一个简单bean对象

package cn.demo.entity;
 /**
  *创建一个下载信息的实体类
  */
 public class DownloadInfo {
     private int threadId;//下载器id
     private int startPos;//开始点
     private int endPos;//结束点
     private int compeleteSize;//完成度
     private String url;//下载器网络标识
     public DownloadInfo(int threadId, int startPos, int endPos,
             int compeleteSize,String url) {
         this.threadId = threadId;
         this.startPos = startPos;
         this.endPos = endPos;
         this.compeleteSize = compeleteSize;
         this.url=url;
     }
     public DownloadInfo() {
     }
     public String getUrl() {
         return url;
     }
     public void setUrl(String url) {
         this.url = url;
     }
     public int getThreadId() {
         return threadId;
     }
     public void setThreadId(int threadId) {
         this.threadId = threadId;
     }
     public int getStartPos() {
         return startPos;
     }
     public void setStartPos(int startPos) {
         this.startPos = startPos;
     }
     public int getEndPos() {
         return endPos;
     }
     public void setEndPos(int endPos) {
         this.endPos = endPos;
     }
     public int getCompeleteSize() {
         return compeleteSize;
     }
     public void setCompeleteSize(int compeleteSize) {
         this.compeleteSize = compeleteSize;
     }
 
     @Override
     public String toString() {
         return "DownloadInfo [threadId=" + threadId
                 + ", startPos=" + startPos + ", endPos=" + endPos
                 + ", compeleteSize=" + compeleteSize +"]";
     }
 }

package cn.demo.entity;
 /**
  *自定义的一个记载下载器详细信息的类 
  */
 public class LoadInfo {
     public int fileSize;//文件大小
     private int complete;//完成度
     private String urlstring;//下载器标识
     public LoadInfo(int fileSize, int complete, String urlstring) {
         this.fileSize = fileSize;
         this.complete = complete;
         this.urlstring = urlstring;
     }
     public LoadInfo() {
     }
     public int getFileSize() {
         return fileSize;
     }
     public void setFileSize(int fileSize) {
         this.fileSize = fileSize;
     }
     public int getComplete() {
         return complete;
     }
     public void setComplete(int complete) {
         this.complete = complete;
     }
     public String getUrlstring() {
         return urlstring;
     }
     public void setUrlstring(String urlstring) {
         this.urlstring = urlstring;
     }
     @Override
     public String toString() {
         return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
                 + ", urlstring=" + urlstring + "]";
     }
 }

这是一个核心类,专门用来处理下载的

package cn.demo.service;
 
 import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import cn.demo.Dao.Dao;
import cn.demo.entity.DownloadInfo;
import cn.demo.entity.LoadInfo;
 
 public class Downloader {
     private String urlstr;// 下载的地址
     private String localfile;// 保存路径
     private int threadcount;// 线程数
     private Handler mHandler;// 消息处理器 
     private int fileSize;// 所要下载的文件的大小
     private Context context; 
     private List<DownloadInfo> infos;// 存放下载信息类的集合
     private static final int INIT = 1;//定义三种下载的状态：初始化状态，正在下载状态，暂停状态
     private static final int DOWNLOADING = 2;
     private static final int PAUSE = 3;
     private int state = INIT;
 
     public Downloader(String urlstr, String localfile, int threadcount,
             Context context, Handler mHandler) {
         this.urlstr = urlstr;
         this.localfile = localfile;
         this.threadcount = threadcount;
         this.mHandler = mHandler;
         this.context = context;
     }
     /**
      *判断是否正在下载 
      */
     public boolean isdownloading() {
         return state == DOWNLOADING;
     }
     /**
      * 得到downloader里的信息
      * 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中
      * 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器
      */
     public LoadInfo getDownloaderInfors() {
         if (isFirst(urlstr)) {
             Log.v("TAG", "isFirst");
             init();
             int range = fileSize / threadcount;
             infos = new ArrayList<DownloadInfo>();
             for (int i = 0; i < threadcount - 1; i++) {
                 DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)* range - 1, 0, urlstr);
                 infos.add(info);
             }
             DownloadInfo info = new DownloadInfo(threadcount - 1,(threadcount - 1) * range, fileSize - 1, 0, urlstr);
             infos.add(info);
             //保存infos中的数据到数据库
             Dao.getInstance(context).saveInfos(infos);
             //创建一个LoadInfo对象记载下载器的具体信息
             LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
             return loadInfo;
         } else {
             //得到数据库中已有的urlstr的下载器的具体信息
             infos = Dao.getInstance(context).getInfos(urlstr);
             Log.v("TAG", "not isFirst size=" + infos.size());
             int size = 0;
             int compeleteSize = 0;
             for (DownloadInfo info : infos) {
                 compeleteSize += info.getCompeleteSize();
                 size += info.getEndPos() - info.getStartPos() + 1;
             }
             return new LoadInfo(size, compeleteSize, urlstr);
         }
     }
 
     /**
      * 初始化
      */
     private void init() {
         try {
             URL url = new URL(urlstr);
             HttpURLConnection connection = (HttpURLConnection) url.openConnection();
             connection.setConnectTimeout(5000);
             connection.setRequestMethod("GET");
             fileSize = connection.getContentLength();
 
             File file = new File(localfile);
             if (!file.exists()) {
                 file.createNewFile();
             }
             // 本地访问文件
             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
             accessFile.setLength(fileSize);
             accessFile.close();
             connection.disconnect();
         } catch (Exception e) {
             e.printStackTrace();
         }
     }  
     /**
      * 判断是否是第一次 下载
      */
     private boolean isFirst(String urlstr) {
         return Dao.getInstance(context).isHasInfors(urlstr);
     }
 
     /**
      * 利用线程开始下载数据
      */
     public void download() {
         if (infos != null) {
             if (state == DOWNLOADING)
                 return;
             state = DOWNLOADING;
             for (DownloadInfo info : infos) {
                 new MyThread(info.getThreadId(), info.getStartPos(),
                         info.getEndPos(), info.getCompeleteSize(),
                         info.getUrl()).start();
             }
         }
     }
 
     public class MyThread extends Thread {
         private int threadId;
         private int startPos;
         private int endPos;
         private int compeleteSize;
         private String urlstr;
 
         public MyThread(int threadId, int startPos, int endPos,
                 int compeleteSize, String urlstr) {
             this.threadId = threadId;
             this.startPos = startPos;
             this.endPos = endPos;
             this.compeleteSize = compeleteSize;
             this.urlstr = urlstr;
         }
         @Override
         public void run() {
             HttpURLConnection connection = null;
             RandomAccessFile randomAccessFile = null;
             InputStream is = null;
             try {
                 URL url = new URL(urlstr);
                 connection = (HttpURLConnection) url.openConnection();
                 connection.setConnectTimeout(5000);
                 connection.setRequestMethod("GET");
                 // 设置范围，格式为Range：bytes x-y;
                 connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);
 
                 randomAccessFile = new RandomAccessFile(localfile, "rwd");
                 randomAccessFile.seek(startPos + compeleteSize);
                 // 将要下载的文件写到保存在保存路径下的文件中
                 is = connection.getInputStream();
                 byte[] buffer = new byte[4096];
                 int length = -1;
                 while ((length = is.read(buffer)) != -1) {
                     randomAccessFile.write(buffer, 0, length);
                     compeleteSize += length;
                     // 更新数据库中的下载信息
                     Dao.getInstance(context).updataInfos(threadId, compeleteSize, urlstr);
                     // 用消息将下载信息传给进度条，对进度条进行更新
                     Message message = Message.obtain();
                     message.what = 1;
                     message.obj = urlstr;
                     message.arg1 = length;
                     mHandler.sendMessage(message);
                     if (state == PAUSE) {
                         return;
                     }
                 }
             } catch (Exception e) {
                 e.printStackTrace();
             }  
         }
     }
     //删除数据库中urlstr对应的下载器信息
     public void delete(String urlstr) {
      Dao.getInstance(context).delete(urlstr);
     }
     //设置暂停
     public void pause() {
         state = PAUSE;
     }
     //重置下载状态
     public void reset() {
         state = INIT;
     }
 }

以下是些xml文件

<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content">
     <LinearLayout
            android:orientation="horizontal"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="5dip">
         <TextView 
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:id="@+id/tv_resouce_name"/>
         <Button
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="下载"
             android:id="@+id/btn_start"
             android:onClick="startDownload"/>
         <Button
             android:layout_width="fill_parent"
             android:layout_height="wrap_content"
             android:layout_weight="1"
             android:text="暂停"
             android:visibility="gone"
             android:id="@+id/btn_pause"
             android:onClick="pauseDownload"/>
       </LinearLayout>
 </LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:id="@+id/llRoot">
     <ListView android:id="@android:id/list"
         android:layout_width="fill_parent"
         android:layout_height="fill_parent">
     </ListView>
 </LinearLayout>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="cn.demo.download"
    android:versionCode="1"
    android:versionName="1.0">

    <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="8" />
 <uses-permission android:name="android.permission.INTERNET"/>　
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <application android:label="@string/app_name"
        android:icon="@drawable/ic_launcher"
        android:theme="@style/AppTheme">
  <activity
             android:name=".MainActivity" 
             android:label="@string/app_name" >
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" /> 
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
    </application>

</manifest>

运行效果如下

源码下载地址