转：关于android多任务同时下载的一点心得

学习android快两个月了，一直坚持从迷茫中寻找可以得到的尽可能多的东西

想做一个下载功能，当然理想的功能要支持多任务同时下载，断点续传的功能，我想一步一步来，首先困难摆在了多任务这里

开始我的思路是在一个Service中启动下载的流操作，然后通过Service中声明一个Activity中的Handler更新UI(比如进度条。。。)

可是我发现在Service中声明一个Activity中的Handler是做不到的（可能只是我做不到吧，无法申请内存）

于是，我决定在Activity中直接启动线程，让其运行，调用自身的Handler来更新UI，没想到在这个下载Activity onPause（）的时候，线程还是活的，也就是说可以继续下载，下例是我做的一个两个任务同时下载的小例子，后面会把理想中的功能都陆续添加上的。。。

 

package oneRain.MulThreadDownload;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import oneRain.MulThreadDownload.DownloadServicer.DownloadThread;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MulThreadDownload extends Activity
{
    /** Called when the activity is first created. */
    private ProgressBar pb1 = null;
    private TextView tv1 = null;
    private ProgressBar pb2 = null;
    private TextView tv2 = null;
    
    private String root = Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator;
    private String downloadFile = "http://192.168.1.5/android/test.zip";
    private String downloadFile1 = "http://192.168.1.5/android/test1.exe";
    
    //声明已经读过的长度变量
    private int hasRead = 0;
    
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        pb1 = (ProgressBar)findViewById(R.id.progressBar1);
        tv1 = (TextView)findViewById(R.id.textView1);
        
        pb2 = (ProgressBar)findViewById(R.id.progressBar2);
        tv2 = (TextView)findViewById(R.id.textView2);
        
        
        download(downloadFile, root, pb1, tv1);
        
        download(downloadFile1, root, pb2, tv2);
    }
    
    private void download(String url, String targetPath, ProgressBar pb, TextView tv)
    {
        DownloadThread dt = new DownloadThread(url, targetPath, pb, tv);
        
        dt.start();
    }
    
    
  //自定义一个Handler类，处理线程消息
    public class MyHandler extends Handler
    {      
        private ProgressBar progressBar;
        private TextView textView;
        
        //通过构造函数来确定给哪个ProgressBar刷新
        public MyHandler(ProgressBar progressBar, TextView textView)
        {
            this.progressBar = progressBar;
            this.textView = textView;
        }
        
        //万恶的动词和名词
        public void handleMessage(Message msg)
        {        
            this.progressBar.setProgress(msg.arg1);
            this.textView.setText(msg.arg1 + "%");
            
            super.handleMessage(msg);    
        }
    }
    
    //下载线程
    public class DownloadThread extends Thread
    {
        private String url = "";
        private String targetPath = "";
        
        private int hasDownload = 0;
        
        private int len = -1;
        private byte buffer[] = new byte[4 * 1024];
        private int size = 0;
        private int rate = 0;
        
        private MyHandler myHandler = null;
        private Message msg = null;
        
        private ProgressBar pb = null;
        private TextView tv = null;
        
        public DownloadThread(String url, String targetPath, ProgressBar pb, TextView tv)
        {
            this.url = url;
            this.targetPath = targetPath;
            
            this.pb = pb;
            this.tv = tv;
            
            myHandler = new MyHandler(this.pb, this.tv);
        }
        
        public void run()
        {
            String targetFileName = this.targetPath + this.url.substring(this.url.lastIndexOf("/")+1, this.url.length());
            File downloadFile = new File(targetFileName);
            
            if(!downloadFile.exists())  
            {
                try 
                {
                    downloadFile.createNewFile();
                } 
                catch (IOException e)
                {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            
            try 
            {
                URL fileUrl = new URL(this.url);
                HttpURLConnection conn = (HttpURLConnection)fileUrl.openConnection();
                
                //获取文件大小
                size = conn.getContentLength();
                
                InputStream is = conn.getInputStream();
                
                OutputStream os = new FileOutputStream(targetFileName);
                
                while((len=is.read(buffer)) != -1)
                {
                    os.write(buffer);
                    
                    hasDownload += len;
                    
                    rate = (hasDownload*100/size);
                    
                    msg = new Message();
                    
                    msg.arg1 = rate;
                    
                    myHandler.sendMessage(msg);
                    
                    System.out.println(rate + "%");
                }  
            }
            catch (MalformedURLException e) 
            {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }  
            
        }
    }
    
}

  转自：http://blog.csdn.net/oneRain88/archive/2011/04/14/6323387.aspx