main.xml：
复制代码 代码如下:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView android:id="@+id/tv"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text=""
/>
<ProgressBar android:id="@+id/down_pb"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:max="100"
style="?android:attr/progressBarStyleHorizontal" mce_style="?android:attr/progressBarStyleHorizontal"
/>
</LinearLayout>

main.java:
复制代码 代码如下:
package com.pocketdigi.download;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import org.apache.http.client.ClientProtocolException;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
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 pb;
TextView tv;
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:
pb.setMax(fileSize);
case 1:
pb.setProgress(downLoadFileSize);
int result = downLoadFileSize * 100 / fileSize;
tv.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);
pb=(ProgressBar)findViewById(R.id.down_pb);
tv=(TextView)findViewById(R.id.tv);
new Thread(){
public void run(){
try {
down_file("http://wallpaper.pocketdigi.com/upload/1/bigImage/1284565196.jpg","/sdcard/");
//下载文件，参数：第一个URL，第二个存放路径
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}.start();
}
public void down_file(String url,String path) throws IOException{
//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);
}
}

大家看了以后就应该明白了，上面写的是用一个循环来完成的这些事情，byte buf[] = new byte[1024];这句话中大家一定要写1024，这个可不能改变呀。sendMsg(0);这句的括号里写的是0，这个也要记得，是0而不是1.