AsyncTask异步类的简单操作

package com.example.day9;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {

    private Button bt1;
    private ProgressDialog dialog;
    private String url="http://b.hiphotos.baidu.com/image/w%3D2048/sign=0240c37eb0119313c743f8b051000dd7/e4dde71190ef76c6f6ecf6979f16fdfaaf51674b.jpg";
    private ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.imageView=(ImageView)super.findViewById(R.id.iv);
        this.dialog=new ProgressDialog(this);
        this.dialog.setTitle("提示框");
        this.dialog.setMessage("正在下载图片..");
        this.bt1=(Button)super.findViewById(R.id.bt1);
        this.bt1.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                new ImageDowload().execute(url);
            }
        });

    }
     public class ImageDowload extends AsyncTask<String, Void, Bitmap>{
         //第一个参数为任务，这里指的是下载链接
         //第二个参数是进度，一般是Integer
         //第三个参数是执行结果返回类型，这里是图片
         public Bitmap doInBackground(String... arg0) {
            // 耗时操作在这里执行，参数为任务类型，这里是指下载链接（String）
            HttpClient client=new DefaultHttpClient();
            HttpGet httpGet=new HttpGet(arg0[0]);
            Bitmap bitmap=null;
            Log.i("lcw", arg0[0]);
            try {
                HttpResponse httpResponse = client.execute(httpGet);
                if(httpResponse.getStatusLine().getStatusCode()==200){
                    Log.i("www", httpResponse+"");
                    HttpEntity entity=httpResponse.getEntity();
                    byte data[]=EntityUtils.toByteArray(entity);
                    bitmap=BitmapFactory.decodeByteArray(data, 0, data.length);
                }
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            return bitmap;
        }

        @Override
        public void onPostExecute(Bitmap result) {
            // 最后操作，更新UI操作
            super.onPostExecute(result);
            Log.i("11111111", "eeee");
            MainActivity.this.imageView.setImageBitmap(result);
            dialog.dismiss();
        }

        @Override
        public void onPreExecute() {
            // 最早操作，预处理动作
            super.onPreExecute();
            MainActivity.this.dialog.show();
        }

    }

}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context="com.example.day9.MainActivity"
    tools:ignore="MergeRootFrame" >

   <ImageView
       android:id="@+id/iv"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
        />

    <Button
        android:id="@+id/bt1"
        android:layout_height="wrap_content"
        android:layout_width="fill_parent"
        android:layout_alignParentBottom="true"
        android:text="点击下载图片"
        />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.day9"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.day9.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

效果图如下：