1.显示进度条
2.启动耗时的网络图片现在程序（线程）并发送消息
3.Handler根据消息判断下载进度并更新UI.
主程序：
package com.tangzq;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
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.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
public class Download_Progressbar extends Activity implements OnClickListener {
private static final String LOG_TAG="Download_Progressbar";
String imgHttp1="http://cdn.androidcommunity.com/wp-content/uploads/2011/03/Playbook_android_apps.jpg";
private TextView txt;
private Button downImg;
private ImageView imgView;
private ProgressBar progressBar;
private Bitmap bitmap;
private static final int LOADING=1;
private static final int END=2;
int maxSize=0;
int nowSize=0;
Handler handler;
private static final String SDCARD="/sdcard/";
private String fileName="networkimg1.png";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.download_progressbar);
txt=(TextView)findViewById(R.id.txt);
downImg=(Button)findViewById(R.id.downImg);
downImg.setOnClickListener(this);
imgView=(ImageView)findViewById(R.id.imgView);
progressBar=(ProgressBar)findViewById(R.id.progressBar);
//progressBar.setVisibility(View.GONE);
handler=new Handler(){
@Override
public void handleMessage(Message msg) {
//super.handleMessage(msg);
if(null!=progressBar){
//设置进度条最大值
progressBar.setMax(maxSize);
//当前已经下载的值
nowSize+=msg.getData().getInt("loadingSize");
//设置进度条的当前进度值
progressBar.setProgress(nowSize);
if(msg.what==LOADING){
//显示已经下载的值
txt.setText("已下载："+(nowSize*100)/maxSize+"%");
Log.e("Download_Progressbar", "正在下载："+nowSize);
}
if(msg.what==END){
//下载完成后隐藏进度条
progressBar.setVisibility(View.INVISIBLE);
//显示图片
imgView.setImageBitmap(bitmap);
//将图片保存到sdcard中
saveImg(SDCARD+fileName,bitmap);
//结束当前线程
Thread.currentThread().interrupt();
}
}
}
};
}
@Override
public void onClick(View paramView) {
//首先清空图片和进度条
if(null!=bitmap){
imgView.setImageBitmap(null);
nowSize=0;
progressBar.setProgress(0);
txt.setText("即将下载......");
}
//1、显示进度条
progressBar.setVisibility(View.VISIBLE);
//2、开始下载
new MyThread(imgHttp1).start();
}
//保存图片方法
public void saveImg(String fullPath,Bitmap bitmap){
File file=new File(fullPath);
if(file.exists()){
file.delete();
}
try {
FileOutputStream fos=new FileOutputStream(file);
boolean isSaved=bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
if(isSaved){
fos.flush();
fos.close();
}
Log.e(LOG_TAG, "文件保存成功");
} catch (FileNotFoundException e) {
Log.e(LOG_TAG, "保存失败");
e.printStackTrace();
} catch (IOException e) {
Log.e(LOG_TAG, "保存失败");
e.printStackTrace();
}
}
class MyThread extends Thread{
String httpImg;
public MyThread(String httpImg){
this.httpImg=httpImg;
}
@Override
public void run() {
//super.run();
ByteArrayOutputStream bos=new ByteArrayOutputStream();
try {
URL url=new URL(httpImg);
HttpURLConnection con=(HttpURLConnection)url.openConnection();
con.setDoInput(true);
con.connect();
InputStream is=con.getInputStream();
//获取文件的大小
maxSize=con.getContentLength();
byte []buffer=new byte[1024];
int len=-1;
while((len=is.read(buffer))!=-1){
bos.write(buffer,0,len);
bos.flush();
//发送消息
Message msg=new Message();
msg.what=LOADING;
Bundle bundle=new Bundle();
bundle.putInt("loadingSize", len);
msg.setData(bundle);
Thread.sleep(100);
handler.sendMessage(msg);
}
//关闭输入流
is.close();
//关闭连接
con.disconnect();
byte []imgBytes=bos.toByteArray();
bitmap=BitmapFactory.decodeByteArray(imgBytes, 0, imgBytes.length);
//下载结束后发送消息
Message msg=new Message();
msg.what=END;
handler.sendMessage(msg);
} catch (MalformedURLException e) {
Log.e("Download_Progressbar", "MalformedURLException");
e.printStackTrace();
} catch (IOException e) {
Log.e("Download_Progressbar", "IOException");
e.printStackTrace();
} catch (InterruptedException e) {
Log.e("Download_Progressbar", "InterruptedException");
e.printStackTrace();
}
}
}
}
download_progressbar.xml代码：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="一步下载图片"
android:id="@+id/txt"/>
<Button
android:id="@+id/downImg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="开始下载图片" />
<FrameLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<ImageView
android:id="@+id/imgView"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<ProgressBar
android:id="@+id/progressBar"
android:layout_width="fill_parent"
style="?android:attr/progressBarStyleHorizontal"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:visibility="invisible"
/>
</FrameLayout>
</LinearLayout>
截图：