android实现图片下载到sdcard中的例子，用进度条显示现在进度，同时间图片显示出来

package com.acer.download;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
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 android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.content.DialogInterface;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.FrameLayout;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class Download extends Activity  {
/** Called when the activity is first created. */
private EditText url;
private Button  download;
private ProgressBar progress;
private String url_address;
private Bitmap bitmap=null;
private FrameLayout frameLayout;
private int file_length;
private int downloadfilesize=0;
private String downloadPath=Environment.getExternalStorageDirectory().getAbsolutePath();
private String Url_address;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

findViews();
setListener();
}

//get the widget
private void findViews(){
url=(EditText)this.findViewById(R.id.url);
download=(Button)this.findViewById(R.id.download);
frameLayout=(FrameLayout)this.findViewById(R.id.frameLayout);
progress=(ProgressBar)this.findViewById(R.id.progress);
progress.setVisibility(View.GONE);
progress.incrementProgressBy(1);
}

//handle the users action
private void setListener(){
download.setOnClickListener(download_start);
}

//send the message to hander function
private void sendMsg(int flag)
{
Message msg = new Message();
msg.what = flag;
handler.sendMessage(msg);
}
//view the picture
private  Handler handler=new Handler(){
public void handleMessage(Message msg){
switch(msg.what)
{
case 0:
progress.setMax(file_length);
break;
case 1:
progress.setProgress(downloadfilesize);
break;
case 2:
//view the picture which read from the sdcard
String my_image_path="/sdcard/image.jpg";
BitmapFactory.Options options=new BitmapFactory.Options();
bitmap=BitmapFactory.decodeFile(my_image_path,options);
ImageView view=(ImageView)frameLayout.findViewById(R.id.image);
view.setImageBitmap(bitmap);
progress.setVisibility(view.GONE);  //dismiss the progressBar
break;
}
super.handleMessage(msg);
}

};
// the function is to test the URL is ends with the given Strings or not
private boolean formatValid(String str){
String str1;
str1=str.toLowerCase();
if(str1.endsWith(".png")||str1.endsWith(".jpg")||str1.endsWith(".gif")||str1.endsWith(".bmp"))
return true;
return false;
}

//handle the button's click
public OnClickListener download_start=new Button.OnClickListener(){
public void onClick(final View view){
progress.setVisibility(view.VISIBLE);  //view the progressBar
progress.setProgress(0);

//test the HTTP_URL is right or not
String myUrl=url.getText().toString();
if(formatValid(myUrl))
{
Url_address=myUrl;
}
else
{
Toast.makeText(Download.this,"please input the right URl_address!", Toast.LENGTH_SHORT).show();
return;
}

//connect to the server and get the resource of picture
new Thread(){
public void run(){
try{
//start the HTTP connection
URL url_address=new URL(Url_address);
HttpURLConnection conn=(HttpURLConnection)url_address.openConnection();
conn.setDoInput(true);
conn.connect();
InputStream inputStream=conn.getInputStream();

file_length=conn.getContentLength();
if (file_length <= 0) throw new RuntimeException(" can not get the inputStream ");
if (inputStream == null) throw new RuntimeException("stream is null");
FileOutputStream output=new FileOutputStream("/sdcard/"+"image.jpg");  //storage the download file

byte[] data=new byte[4096];
int count=0;
sendMsg(0); //initialize the progressBar

do
{
count= inputStream.read(data);
if (count == -1)
{
break;
}
output.write(data, 0, count);
downloadfilesize+= count;
sendMsg(1);    //update the progressBar
} while (true);

sendMsg(2);   //view the picture

}catch(MalformedURLException e1){
e1.printStackTrace();
}catch(IOException e){
e.printStackTrace();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}.start();

}//end of onClick()
};
}//end of the Download

<?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"
>
<EditText android:id="@+id/url"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text=""
/>
<Button android:id="@+id/download"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="start the download">
</Button>

<ProgressBar android:id="@+id/progress"
style="?android:attr/progressBarStyleHorizontal" mce_style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
</ProgressBar>

<FrameLayout android:id="@+id/frameLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<ImageView android:id="@+id/image"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="centerInside"
android:padding="2dp">
</ImageView>
</FrameLayout>

</LinearLayout>