android异步任务之AsyncTask（以加载网络图片替例子）

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示例最终效果图：

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AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.lesson"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk        android:minSdkVersion="7"        android:targetSdkVersion="7" />            <!-- 用于访问网络的授权 -->    <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.lesson.MainActivity">             <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

?基本布局文件activity_main.xml：一个ImageView和一个Button

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent" >    <ImageView        android:id="@+id/imageView1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentTop="true"        android:layout_centerHorizontal="true"        android:layout_marginTop="48dp"/>            <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentBottom="true"        android:layout_centerHorizontal="true"        android:text="下载图片" /></RelativeLayout>

?MainActivity.java

/* * 异步任务实现activity中加载网络图片 */package com.lesson;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.InputStream;import org.apache.http.HttpResponse;import org.apache.http.client.ClientProtocolException;import org.apache.http.client.HttpClient;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.DefaultHttpClient;import android.app.Activity;import android.app.ProgressDialog;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.os.Bundle;import android.test.AndroidTestCase;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends Activity {	private Button button;private ProgressDialog progerssDialog;private ImageView imageView;//要加载的图片private final String url="http://www.windows7en.com/desk/UploadFiles_7433/201006/2010060910062279.jpg";	@Override	protected void onCreate(Bundle savedInstanceState) {				super.onCreate(savedInstanceState);		this.setContentView(R.layout.activity_main);		button=(Button)findViewById(R.id.button1);		imageView=(ImageView)findViewById(R.id.imageView1);		progerssDialog=new ProgressDialog(this);		progerssDialog.setCancelable(false);		//设置进度条水平加载				progerssDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);		button.setOnClickListener(new OnClickListener() {					@Override			public void onClick(View arg0) {				//异步任务调用				new ImageUpdate().execute(url);							}		});	}class ImageUpdate extends AsyncTask<String, Integer,byte[]>{	//线程启动时，该方法被调用次序:2	@Override	protected byte[] doInBackground(String... arg0) {		HttpGet httpGet=new HttpGet(arg0[0]);		InputStream inputStream=null;		byte[] result=null;		byte[] data=new byte[1024];		HttpClient client = new DefaultHttpClient();		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();		try {			HttpResponse httpResponse=client.execute(httpGet);//得到响应			if(httpResponse.getStatusLine().getStatusCode()==200){								inputStream=httpResponse.getEntity().getContent();				//文件总长度				int filelenth=(int) httpResponse.getEntity().getContentLength();				int readlength=0;				int totallenth=0;				while((readlength=inputStream.read(data))!=-1){					totallenth+=readlength;                                 //用于进度条刻度计算公式					int progressValue= (int)((totallenth/(float)filelenth)*100);                                 //将刻度值传递到第2步					publishProgress(progressValue);					outputStream.write(data, 0, readlength);				}				result=outputStream.toByteArray();			}					} catch (ClientProtocolException e) {						e.printStackTrace();		} catch (IOException e) {						e.printStackTrace();		}finally{			client.getConnectionManager().shutdown();		}		return result;	}//线程启动时，该方法被调用次序:4@Override protected void onPostExecute(byte[] result) { // TODO Auto-generated method stub super.onPostExecute(result); Bitmap bitmap=BitmapFactory.decodeByteArray(result, 0, result.length); imageView.setImageBitmap(bitmap); progerssDialog.dismiss(); }//线程启动时，该方法被调用次序:1@Override protected void onPreExecute() { super.onPreExecute(); //加载图片时的进度显示对话框 progerssDialog.show(); }//线程启动时，该方法被调用次序:3@Override protected void onProgressUpdate(Integer... values) {  super.onProgressUpdate(values); progerssDialog.setProgress(values[0]); } } }

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