android 多線程斷點續傳下載

時間 2019-12-19

原文原文鏈接

今天跟你們一塊兒分享下Android開發中比較難的一個環節,可能不少人看到這個標題就會感受頭很大,的確若是沒有良好的編碼能力和邏輯思惟,這塊是很難搞明白的,前面2次總結中已經爲你們分享過有關技術的一些基本要領,咱們先一塊兒簡單回顧下它的基本原理。java

http://blog.csdn.net/shimiso/article/details/6763664 android 多線程斷點續傳下載一android

http://blog.csdn.net/shimiso/article/details/6763986 android 多線程斷點續傳下載二算法

什麼是多線程下載？sql

多線程下載其實就是迅雷,BT一些下載原理,經過多個線程同時和服務器鏈接,那麼你就能夠榨取到較高的帶寬了,大體作法是將文件切割成N塊,每塊交給單獨一個線程去下載,各自下載完成後將文件塊組合成一個文件,程序上要完成作切割和組裝的小算法數據庫

什麼是斷點續傳?數組

斷點續傳,就是當咱們下載未結束時候,退出保存下載進度,當下次打開繼續下載的時接着上次的進度繼續下載,不用每次下載都從新開始,那麼有關斷點續傳的原理和實現手段,可參考我之前的一篇總結http://blog.csdn.net/shimiso/article/details/5956314 裏面詳細講解http協議斷點續傳的原理,務必要看懂,不然你沒法真正理解本節代碼服務器

怎麼完成多線程斷點續傳?網絡

將二者合二爲一須要程序記住每一個文件塊的下載進度,並保存入庫,當下載程序啓動時候你須要判斷程序是否已經下載過該文件,並取出各個文件塊的保存記錄,換算出下載進度繼續下載,在這裏你須要掌握Java多線程的基本知識,handler的使用,以及集合,算法,文件操做等基本技能,同時還要解決sqlite數據庫的同步問題,由於它是不太怎麼支持多線程操做的,控制很差常常會出現庫被鎖定的異常,同時在android2.3之後就不能activity中直接操做http,不然你將收到系統送上的NetworkOnMainThreadException異常,在UI體驗上必定記住要使用異步完成,既然大體思路已經清楚,下面咱們開始分析程序:數據結構

package cn.demo.DBHelper;
 
 import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
 
     /**
      * 創建一個數據庫幫助類
      */
 public class DBHelper extends SQLiteOpenHelper {
     //download.db-->數據庫名
     public DBHelper(Context context) {
         super(context, "download.db", null, 1);
     }
     
     /**
      * 在download.db數據庫下建立一個download_info表存儲下載信息
      */
     @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) {
 
     }
 
 }

數據庫操做要藉助單例和同步,來保證線程的執行順序,以避免多個線程爭相搶用sqlite資源致使異常出現多線程

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;

/**
 * 
 * 一個業務類
 */
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;
    }

    /**
     * 查看數據庫中是否有數據
     */
    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 下載的具體信息
     */
    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();
            }
        }
    }

    /**
     * 獲得下載具體信息
     */
    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;
    }

    /**
     * 更新數據庫中的下載信息
     */
    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();
            }
        }
    }

    /**
     * 下載完成後刪除數據庫中的數據
     */
    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;
      
        
     
    }
    
}

注意子線程不要影響主UI線程,靈活運用task和handler,各取所長,保證用戶體驗,handler一般在主線程中有利於專門負責處理UI的一些工做

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 { 
     // 固定下載的資源路徑，這裏能夠設置網絡上的地址
     private static final String URL = "http://download.haozip.com/";
     // 固定存放下載的音樂的路徑：SD卡目錄下
     private static final String SD_PATH = "/mnt/sdcard/";
     // 存放各個下載器
     private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
     // 存放與下載器對應的進度條
     private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
     /**
      * 利用消息處理機制適時更新進度條
      */
     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) {
                     // 設置進度條按讀取的length長度更新
                     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()+"]下載完成！", Toast.LENGTH_SHORT).show();
                         // 下載完成後清除進度條並將map中的數據清空
                         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();
     }
     // 顯示listView，這裏能夠隨便添加
     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);
         
     }
     /**
      * 響應開始下載按鈕的點擊事件
      */
     public void startDownload(View v) {
         // 獲得textView的內容 
         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;
         //設置下載線程數爲4，這裏是我爲了方便隨便固定的
         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]);
             // 初始化一個downloader下載器
             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;
             // 獲得下載信息類的個數組成集合
             return downloader.getDownloaderInfors(); 
        }
        @Override
        protected void onPostExecute(LoadInfo loadInfo) {
            if(loadInfo!=null){
                 // 顯示進度條
                 showProgress(loadInfo, urlstr, v);
                 // 調用方法開始下載
                 downloader.download();
            } 
        }
         
     };
     /**
      * 顯示進度條
      */
     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);
         }
     }
     /**
      * 響應暫停下載按鈕的點擊事件
      */
     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);
     }
 }

這是一個信息的實體,記錄了一些字典信息,能夠認爲是一個簡單bean對象

package cn.demo.entity;
 /**
  *建立一個下載信息的實體類
  */
 public class DownloadInfo {
     private int threadId;//下載器id
     private int startPos;//開始點
     private int endPos;//結束點
     private int compeleteSize;//完成度
     private String url;//下載器網絡標識
     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;
 /**
  *自定義的一個記載下載器詳細信息的類 
  */
 public class LoadInfo {
     public int fileSize;//文件大小
     private int complete;//完成度
     private String urlstring;//下載器標識
     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 + "]";
     }
 }

這是一個核心類,專門用來處理下載的

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;// 下載的地址
     private String localfile;// 保存路徑
     private int threadcount;// 線程數
     private Handler mHandler;// 消息處理器 
     private int fileSize;// 所要下載的文件的大小
     private Context context; 
     private List<DownloadInfo> infos;// 存放下載信息類的集合
     private static final int INIT = 1;//定義三種下載的狀態：初始化狀態，正在下載狀態，暫停狀態
     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;
     }
     /**
      *判斷是否正在下載 
      */
     public boolean isdownloading() {
         return state == DOWNLOADING;
     }
     /**
      * 獲得downloader裏的信息
      * 首先進行判斷是不是第一次下載，若是是第一次就要進行初始化，並將下載器的信息保存到數據庫中
      * 若是不是第一次下載，那就要從數據庫中讀出以前下載的信息（起始位置，結束爲止，文件大小等），並將下載信息返回給下載器
      */
     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中的數據到數據庫
             Dao.getInstance(context).saveInfos(infos);
             //建立一個LoadInfo對象記載下載器的具體信息
             LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
             return loadInfo;
         } else {
             //獲得數據庫中已有的urlstr的下載器的具體信息
             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();
             }
             // 本地訪問文件
             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
             accessFile.setLength(fileSize);
             accessFile.close();
             connection.disconnect();
         } catch (Exception e) {
             e.printStackTrace();
         }
     }  
     /**
      * 判斷是不是第一次 下載
      */
     private boolean isFirst(String urlstr) {
         return Dao.getInstance(context).isHasInfors(urlstr);
     }
 
     /**
      * 利用線程開始下載數據
      */
     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");
                 // 設置範圍，格式爲Range：bytes x-y;
                 connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);
 
                 randomAccessFile = new RandomAccessFile(localfile, "rwd");
                 randomAccessFile.seek(startPos + compeleteSize);
                 // 將要下載的文件寫到保存在保存路徑下的文件中
                 is = connection.getInputStream();
                 byte[] buffer = new byte[4096];
                 int length = -1;
                 while ((length = is.read(buffer)) != -1) {
                     randomAccessFile.write(buffer, 0, length);
                     compeleteSize += length;
                     // 更新數據庫中的下載信息
                     Dao.getInstance(context).updataInfos(threadId, compeleteSize, urlstr);
                     // 用消息將下載信息傳給進度條，對進度條進行更新
                     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();
             }  
         }
     }
     //刪除數據庫中urlstr對應的下載器信息
     public void delete(String urlstr) {
         Dao.getInstance(context).delete(urlstr);
     }
     //設置暫停
     public void pause() {
         state = PAUSE;
     }
     //重置下載狀態
     public void reset() {
         state = INIT;
     }
 }

如下是些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="下載"
             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="暫停"
             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>