android异步任务学习笔记

android异步任务可以很方便的完成耗时操作并更新UI，不像多线程还要利用消息队列，子线程发消息给主线程，主线程才能更新UI。总之，android异步任务把多线程的交互进行进一步的封装，用起来跟方便。

如下是异步任务demo代码:

完成异步下载图片，更新界面。

package com.example.android_async_task2;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.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.ProgressDialog;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.os.Bundle;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends Activity {private Button btn=null;private ImageView image=null;private String image_path="http://f2.sjbly.cn/m13/0729/1459/6947edn_690x459_b.jpg";private ProgressDialog dialog;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btn=(Button)this.findViewById(R.id.button1);dialog=new ProgressDialog(this);dialog.setTitle("提示信息");dialog.setMessage("下载中，请稍等......");//设置进度条的样式dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);//屏幕不失去焦点dialog.setCancelable(false);image=(ImageView)this.findViewById(R.id.imageView1);btn.setOnClickListener(new OnClickListener(){@Overridepublic void onClick(View v) {new MyTask().execute(image_path);}});}public class MyTask extends AsyncTask<String,Integer,Bitmap>{@Overrideprotected void onPreExecute() {dialog.show();super.onPreExecute();}@Overrideprotected Bitmap doInBackground(String... params) {//定义一个内存流，不需要关闭ByteArrayOutputStream out= new ByteArrayOutputStream();//定义一个输入流InputStream in=null;Bitmap bitmap=null;//通过HttpClient类获取网络资源HttpClient httpClient=new DefaultHttpClient();//设置请求方式(注意请求地址URL要写入！！！)HttpGet httpGet=new HttpGet(params[0]);try {//获得请求状态HttpResponse httpResponse=httpClient.execute(httpGet);//判断请求状态结果码if(httpResponse.getStatusLine().getStatusCode()==200){/*//通过一个实体类获得响应的实体HttpEntity httpEntity=httpResponse.getEntity();//通过一个实体工具类获得实体的字节数组byte[]data=EntityUtils.toByteArray(httpEntity);//通过工厂类创建Bitmap对象BitmapFactory.decodeByteArray(data, 0, data.length);*///获得输入流in=httpResponse.getEntity().getContent();//获得文件的总长度long file_length=httpResponse.getEntity().getContentLength();//计算总长度int total_len=0;int len=0;byte[] buffer=new byte[1024];try{while((len=in.read(buffer))!=-1){total_len+=len;<span style="color:#ff0000;">//刻度计算公式</span>int value=(int)(total_len/((float)file_length)*100);<span style="color:#ff6666;">//发布进度条的刻度</span>publishProgress(value);//写入输出流out.write(buffer, 0, len);}//内存输出流转换成字节数组bitmap=BitmapFactory.decodeByteArray(out.toByteArray(), 0, out.toByteArray().length);}catch(Exception e){}finally{if(in!=null){in.close();}}}} catch (ClientProtocolException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}return bitmap;}@Overrideprotected void onPostExecute(Bitmap result) {super.onPostExecute(result);image.setImageBitmap(result);dialog.dismiss();}@Overrideprotected void onProgressUpdate(Integer... values) {super.onProgressUpdate(values);dialog.setProgress(values[0]);}}@Overridepublic boolean onCreateOptionsMenu(Menu menu) {// Inflate the menu; this adds items to the action bar if it is present.getMenuInflater().inflate(R.menu.main, menu);return true;}}

其中

publishProgress(value);

是可以发送几个对象给

onProgressUpdate()方法的。

DEMO下载：http://download.csdn.net/detail/u014600432/8175337

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