我们之前讲过handler+Thread实现非UI线程更新UI界面的例子，这一次我们讲个更好用的异步，我们同样可以使用这个异步来实现之前的功能
[java]
package com.gaoxueping;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.RecoverySystem.ProgressListener;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {

private Button execute, cancel;
private ProgressBar progressBar;
private TextView textView;
private MyTask mTask;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

execute = (Button) findViewById(R.id.execute);
execute.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
mTask = new MyTask();
mTask.execute("http://www.baidu.com");

}
});

progressBar = (ProgressBar) findViewById(R.id.progress_bar);
textView = (TextView) findViewById(R.id.text_view);
}

@Override
public 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;
}

private class MyTask extends AsyncTask<String, Integer, String>{

@Override
protected void onCancelled() {
// TODO Auto-generated method stub
super.onCancelled();
Log.i("canled","onCancelled called");
textView.setText("calced");
progressBar.setProgress(0);
}

@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
Log.i("post","onPostExecute() called");
textView.setText(result);
}

@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
Log.i("pre","onPreExecute() called");
textView.setText("hey,loading......");
}

@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
super.onProgressUpdate(values);
Log.i("updateBar","onProgressUpdate called");
progressBar.setProgress(values[0]);
textView.setText("Loading......" + values[0] + "%");
}

@Override
protected String doInBackground(String... params) {
// TODO Auto-generated method stub
Log.i("backRun","doInBackground() called");
try{
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(params[0]);
HttpResponse response = client.execute(httpGet);
if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
HttpEntity entity = response.getEntity();
InputStream is = entity.getContent();
long total = entity.getContentLength();

ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int count = 0;
int length = -1;
while((length = is.read(buf)) != -1){
baos.write(buf,0,length);
count += length;

publishProgress((int) (count / (float) length) * 100);
Thread.sleep(500);
}

return new String(baos.toByteArray(),"utf8");
}
}catch(Exception e){
e.printStackTrace();
}

return null;
}

}

}
[/java]
布局文件
[xml]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Button
android:id="@+id/execute"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="execute"/>
<Button
android:id="@+id/cancel"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="cancel"/>
<ProgressBar
android:id="@+id/progress_bar"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:progress="0"
android:max="100"
style="?android:attr/progressBarStyleHorizontal"/>
<ScrollView
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/text_view"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</ScrollView>
</LinearLayout>
[/xml]
当然不要忘记加入访问网络的权限。