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：