如何在Android中利用AsyncTask对任务进行异步处理

Activity.runOnUiThread( Runnable ) 
View.post( Runnable ) 
View.postDelayed( Runnable, long ) 
Hanlder 

package test.list; 
import java.io.ByteArrayOutputStream; 
import java.io.InputStream; 
import java.util.ArrayList; 
 
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 android.app.Activity; 
import android.app.ProgressDialog; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.os.Handler; 
import android.os.Message; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
 
public class NetworkActivity extends Activity{ 
 private TextView message; 
 private Button open; 
 private EditText url; 
 
 @Override 
 public void onCreate(Bundle savedInstanceState) { 
  super.onCreate(savedInstanceState); 
  setContentView(R.layout.network); 
  message= (TextView) findViewById(R.id.message); 
  url= (EditText) findViewById(R.id.url); 
  open= (Button) findViewById(R.id.open); 
  open.setOnClickListener(new View.OnClickListener() { 
   public void onClick(View arg0) { 
    connect(); 
   } 
  }); 
 
 } 
 
 private void connect() { 
  PageTask task = new PageTask(this); 
  task.execute(url.getText().toString()); 
 } 
 
 
 class PageTask extends AsyncTask { 
  // 可变长的输入参数，与AsyncTask.exucute()对应 
  ProgressDialog pdialog; 
  public PageTask(Context context){ 
   pdialog = new ProgressDialog(context, 0);  
   pdialog.setButton("cancel", new DialogInterface.OnClickListener() { 
   public void onClick(DialogInterface dialog, int i) { 
   dialog.cancel(); 
   } 
   }); 
   pdialog.setOnCancelListener(new DialogInterface.OnCancelListener() { 
   public void onCancel(DialogInterface dialog) { 
   finish(); 
   } 
   }); 
   pdialog.setCancelable(true); 
   pdialog.setMax(100); 
   pdialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); 
   pdialog.show(); 
 
 
  } 
  @Override 
  protected String doInBackground(String... params) { 
 
   try{ 
 
    HttpClient client = new DefaultHttpClient(); 
    // params[0]代表连接的url 
    HttpGet get = new HttpGet(params[0]); 
    HttpResponse response = client.execute(get); 
    HttpEntity entity = response.getEntity(); 
    long length = entity.getContentLength(); 
    InputStream is = entity.getContent(); 
    String s = null; 
    if(is != null) { 
     ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
 
     byte[] buf = new byte[128]; 
 
     int ch = -1; 
 
     int count = 0; 
 
     while((ch = is.read(buf)) != -1) { 
 
      baos.write(buf, 0, ch); 
 
      count += ch; 
 
      if(length > 0) { 
       // 如果知道响应的长度，调用publishProgress（）更新进度 
       publishProgress((int) ((count / (float) length) * 100)); 
      } 
 
      // 让线程休眠100ms 
      Thread.sleep(100); 
     } 
     s = new String(baos.toByteArray());    } 
    // 返回结果 
    return s; 
   } catch(Exception e) { 
    e.printStackTrace(); 
 
   } 
 
   return null; 
 
  } 
 
  @Override 
  protected void onCancelled() { 
   super.onCancelled(); 
  } 
 
  @Override 
  protected void onPostExecute(String result) { 
   // 返回HTML页面的内容 
   message.setText(result); 
   pdialog.dismiss(); 
  } 
 
  @Override 
  protected void onPreExecute() { 
   // 任务启动，可以在这里显示一个对话框，这里简单处理 
   message.setText(R.string.task_started); 
  } 
 
  @Override 
  protected void onProgressUpdate(Integer... values) { 
   // 更新进度 
    System.out.println(""+values[0]); 
    message.setText(""+values[0]); 
    pdialog.setProgress(values[0]); 
  } 
 
  } 
 
}