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();
}

}
}

}

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