<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_asynctask_downloadimg;

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.Dialog;

import android.app.ProgressDialog;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.view.Menu;

import android.view.View;

import android.widget.ImageView;

/*

 * 下载图片:

 * 1.初始化控件

 * 2.设置下载图片按钮监听

 *     2.1创建一个异步任务类,实现其抽象方法

 *     2.2开启异步任务开始下载

 *         在子线程中进行进行耗时操作下载图片

 *             1)创建HttpCient对象

 * `        2)创建HttpGet对象传入

 *             3)执行请求获得HttpResponse对象

 *             4)获得响应码

 *             5)判断响应码,成功,获得实体对象httpEntity

 *             6)通过HttpEntity对象的getContent()方法得到读取流

 *             7)封装成BitMap对象,并传回给主线程

 *         在主线程中显示图片

 *

 *

 */

public class MainActivity extends Activity {

    private ImageView image;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

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

    }

    //2.设置下载图片按钮监听

    public void onDownLoadImg(View v){

        //new MyAsyncTask().execute("http://c.hiphotos.baidu.com/image/h%3D200/sign=8cbc53a04ded2e73e3e9812cb700a16d/f7246b600c338744513e9358560fd9f9d72aa01f.jpg");

    }

//     2.1创建一个异步任务类,实现其抽象方法

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

        @Override

        protected void onPreExecute() {

            super.onPreExecute();

        }

        @Override

        protected Bitmap doInBackground(String... params) {

            try {

                DefaultHttpClient defaultCLient = new DefaultHttpClient();

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

                HttpResponse response = defaultCLient.execute(httpGet);

                int code = response.getStatusLine().getStatusCode();

                if(code == 200){

                    HttpEntity entity = response.getEntity();

                    InputStream content = entity.getContent();

                    Bitmap result = BitmapFactory.decodeStream(content);

                    return result;

                }

            } 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);

            image.setImageBitmap(result);

        }

    }

}