<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context=".MainActivity" >

    <ImageView

        android:id="@+id/image"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:src="@drawable/ic_launcher"

        android:maxHeight="300dp"

        android:maxWidth="300dp"

        android:adjustViewBounds="true"/>

    <Button

        android:id="@+id/btn_download"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:onClick="onDownLoadImg"

        android:text="点击下载图片"

        android:textSize = "20sp"/>

</LinearLayout>

package com.example.day07_downloadimg_prgress;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import org.apache.http.HttpEntity;

import org.apache.http.HttpResponse;

import org.apache.http.client.ClientProtocolException;

import org.apache.http.client.methods.HttpGet;

import org.apache.http.impl.client.DefaultHttpClient;

import android.os.AsyncTask;

import android.os.Bundle;

import android.app.Activity;

import android.app.ProgressDialog;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.view.Menu;

import android.view.View;

import android.widget.ImageView;

import android.widget.Toast;

/**

 *

        //弹出进度条对话框基本使用

        //创建进度条对话框

        ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);

        //设置标题

        progressDialog.setTitle("正在下载");

        //设置内容

        progressDialog.setMessage("下载中");

        //设置弹出对话框显示的样式

        progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

        //显示

        progressDialog.show();

        //给进度条设置值,在show()之后设置

        progressDialog.setProgress(50);

        //隐藏

        progressDialog.hide();

 *

 *

 */

/**注意:需要在清单文件中添加网络权限

 * 1.初始化控件,数据

 * 2.设置下载点击事件

 *     2.1.开启异步任务下载图片

 *         1.先显示对话框,进度为0

 *         2.开始下载

 *             1.获得文件大小

 *             2.获得当前下载的总量

 *             3.计算当前百分比

 *             4.通知对话框更新更改进度(主线程)

 *             5.下载完成,返回数据

 *         3.下载完成

 *             1.关闭对话框

 *             2.显示下载成功的图片

 * @author my

 *

 */

public class MainActivity extends Activity {

    private ImageView image;

    private static final String imgPath = "http://c.hiphotos.baidu.com/image/h%3D200/sign=8cbc53a04ded2e73e3e9812cb700a16d/f7246b600c338744513e9358560fd9f9d72aa01f.jpg";

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        image = (ImageView) findViewById(R.id.image);

    }

    public void onDownLoadImg(View v){

        new MyAsyncTask().execute(imgPath);

    }

    class MyAsyncTask extends AsyncTask<String, Integer, Bitmap>{

        private ProgressDialog progressDialog;

        @Override

        protected void onPreExecute() {

            super.onPreExecute();

            progressDialog = new ProgressDialog(MainActivity.this);

            progressDialog.setTitle("正在下载");

            progressDialog.setMessage("下载中...");

            progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);

            progressDialog.show();

        }

        @Override

        protected Bitmap doInBackground(String... params) {

            try {

                DefaultHttpClient httpClient = new DefaultHttpClient();

                HttpGet httpGet = new HttpGet(params[0]);

                HttpResponse response = httpClient.execute(httpGet);

                if(200 == response.getStatusLine().getStatusCode()){

                    //获得实体对象

                    HttpEntity entity = response.getEntity();

                    //得到输入流

                    InputStream is = entity.getContent();

                    ByteArrayOutputStream baos = new ByteArrayOutputStream();

                    //获得要下载图片的总长度

                    long contentLength = entity.getContentLength();

                    //当前下载图片的长度

                    int currentLength = 0;

                    byte[] buf = new byte[50];

                    int len = 0;

                    while(-1 !=(len = is.read(buf))){

                        currentLength += len;

                        //计算当前的百分比

                        int percent =(int) ((currentLength/(float)contentLength)*100);

                        //通知调用主线程的方法更新进度,自动调用onProgressUpdate()方法

                        publishProgress(percent);

                        //写到流中

                        baos.write(buf, 0, len);

                        baos.flush();

                    }

                    is.close();

                    baos.close();

                    //把字节流转换成字节数组

                    byte[] byteArray = baos.toByteArray();

                    //把字节流转换成Bitmap

                    Bitmap bitmap = BitmapFactory.decodeByteArray(byteArray, 0, byteArray.length);

                    return bitmap;

                }

            } catch (ClientProtocolException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            } catch (IOException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return null;

        }

        @Override

        protected void onPostExecute(Bitmap result) {

            super.onPostExecute(result);

            //关闭对话框

            progressDialog.dismiss();

            if(result != null){

                image.setImageBitmap(result);

            }else{

                Toast.makeText(MainActivity.this, "网络错误", 0).show();

            }

        }

        //在主线程中执行,参数类型与类定义泛型的第二个参数一致

        @Override

        protected void onProgressUpdate(Integer... values) {

            super.onProgressUpdate(values);

            //更新进度

            progressDialog.setProgress(values[0]);

        }

    }

}