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();

}



}

}



}