Android 中很多地方都需要用到线程下载。下面我谢了个简单的下载图片的demo。望对你们有到帮助.

首先，配置权限，

在 AndroidManifest.xml里面的application节点下面配置需要用到的权限

权限添加完成，布局如下：

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

android:id="@+id/btn_1"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="点击下载图片"

/>

android:id="@+id/tv"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="" />

android:id="@+id/down_pb"

style="?android:attr/progressBarStyleHorizontal"

mce_style="?android:attr/progressBarStyleHorizontal"

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:max="100" />

接来下就是写代码了，代码其实很简单，话不多说，我直接上传：

package com.lh.thread;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.URL;

import java.net.URLConnection;

import android.app.Activity;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.util.Log;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.ProgressBar;

import android.widget.TextView;

import android.widget.Toast;

public class Main extends Activity {

/** Called when the activity is first created. */

ProgressBar mPb;

TextView mTv;

Button mBtn;

int fileSize;

int downLoadFileSize;

String fileEx, fileNa, filename;

private Handler handler = new Handler() {

@Override

public void handleMessage(Message msg) {// 定义一个Handler，用于处理下载线程与UI间通讯

if (!Thread.currentThread().isInterrupted()) {

switch (msg.what) {

case 0:

mPb.setMax(fileSize);

case 1:

mPb.setProgress(downLoadFileSize);

int result = downLoadFileSize * 100 / fileSize;

mTv.setText(result + "%");

break;

case 2:

Toast.makeText(Main.this, "文件下载完成", 1).show();

break;

case -1:

String error = msg.getData().getString("error");

Toast.makeText(Main.this, error, 1).show();

break;

}

}

super.handleMessage(msg);

}

};

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

//初始化控件

mPb = (ProgressBar) findViewById(R.id.down_pb);

mTv = (TextView) findViewById(R.id.tv);

mBtn=(Button) findViewById(R.id.btn_1);

mBtn.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

//启动线程进行下载

new Thread() {

public void run() {

try {

down_file(

"http://att.bbs.duowan.com/forum/201310/23/151916t9kdya2gia0a21la.jpg",

"/sdcard/");

// 下载文件，参数：第一个URL，第二个存放路径

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}.start();

}

});

}

/**

* 此方法描述的是：下载文件并保存

* @param url

* @param path

* @throws IOException void

*/

public void down_file(String url, String path) throws Exception {

Log.i("AAAAAA", "~~~~~~~~~存储路径是"+path);

// 下载函数

filename = url.substring(url.lastIndexOf("/") + 1);

// 获取文件名

URL myURL = new URL(url);

URLConnection conn = myURL.openConnection();

conn.connect();

InputStream is = conn.getInputStream();

this.fileSize = conn.getContentLength();// 根据响应获取文件大小

if (this.fileSize <= 0)

throw new RuntimeException("无法获知文件大小 ");

if (is == null)

throw new RuntimeException("stream is null");

FileOutputStream fos = new FileOutputStream(path + filename);

// 把数据存入路径+文件名

byte buf[] = new byte[1024];

downLoadFileSize = 0;

sendMsg(0);

do {

// 循环读取

int numread = is.read(buf);

if (numread == -1) {

break;

}

fos.write(buf, 0, numread);

downLoadFileSize += numread;

sendMsg(1);// 更新进度条

} while (true);

sendMsg(2);// 通知下载完成

try {

is.close();

} catch (Exception ex) {

Log.e("tag", "error: " + ex.getMessage(), ex);

}

}

private void sendMsg(int flag) {

Message msg = new Message();

msg.what = flag;

handler.sendMessage(msg);

}

}好了，进度条下载就完成了