android 之断点续传详解三部曲之[三] → 多任务同时下载-阿里云开发者社区

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。

三部曲之一：http://blog.csdn.net/gulaer/article/details/8513825

三部曲之二：http://blog.csdn.net/gulaer/article/details/8513916

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/gulaer/article/details/8514146 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:

DBHelper.java

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

Dao.java

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();
			}
		}
	}
}

DownLoadAdapter.java

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

MainActivity.java

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

DownloadInfo.java

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
				+ "]";
	}
}

LoadInfo.java

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

Downloader.java

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.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;
	}
}

下面就是布局文件了：

main.xml

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

    <ListView
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >
    </ListView>

</LinearLayout>

list_item.xml

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

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="5dip"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/tv_resouce_name"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1" />

        <Button
            android:id="@+id/btn_start"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="startDownload"
            android:text="下载" />

        <Button
            android:id="@+id/btn_pause"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="pauseDownload"
            android:text="暂停"
            android:visibility="gone" />
    </LinearLayout>

</LinearLayout>

最后是配置文件：

AndroidManifest.xml

<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>

效果图：

源码下载地址：http://download.csdn.net/detail/gulaer/5005135

原文地址：http://blog.csdn.net/shimiso/article/details/6763986 非常感谢原作者.

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