package com.hilton.effectiveandroid.concurrent; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.AsyncTask; import android.os.Bundle; import android.os.SystemClock; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.ProgressBar; import com.hilton.effectiveandroid.R; /*  * AsyncTask cannot be reused, i.e. if you have executed one AsyncTask, you must discard it, you cannot execute it again.  * If you try to execute an executed AsyncTask, you will get "java.lang.IllegalStateException: Cannot execute task: the task is already running"  * In this demo, if you click "get the image" button twice at any time, you will receive "IllegalStateException".  * About cancellation:  * You can call AsyncTask#cancel() at any time during AsyncTask executing, but the result is onPostExecute() is not called after  * doInBackground() finishes, which means doInBackground() is not stopped. AsyncTask#isCancelled() returns true after cancel() getting  * called, so if you want to really cancel the task, i.e. stop doInBackground(), you must check the return value of isCancelled() in  * doInBackground, when there are loops in doInBackground in particular.  * This is the same to Java threading, in which is no effective way to stop a running thread, only way to do is set a flag to thread, and check  * the flag every time in Thread#run(), if flag is set, run() aborts.  */ public class AsyncTaskDemoActivity extends Activity {     private static final String ImageUrl = "http://i1.cqnews.net/sports/attachement/jpg/site82/2011-10-01/2960950278670008721.jpg";     private ProgressBar mProgressBar;     private ImageView mImageView;     private Button mGetImage;     private Button mAbort;     @Override     public void onCreate(Bundle icicle) {  super.onCreate(icicle);  setContentView(R.layout.async_task_demo_activity);  mProgressBar = (ProgressBar) findViewById(R.id.async_task_progress);  mImageView = (ImageView) findViewById(R.id.async_task_displayer);  final ImageLoader loader = new ImageLoader();  mGetImage = (Button) findViewById(R.id.async_task_get_image);  mGetImage.setOnClickListener(new View.OnClickListener() {      public void onClick(View v) {   loader.execute(ImageUrl);      }  });  mAbort = (Button) findViewById(R.id.asyc_task_abort);  mAbort.setOnClickListener(new View.OnClickListener() {      public void onClick(View v) {   loader.cancel(true);      }  });  mAbort.setEnabled(false);     }     private class ImageLoader extends AsyncTask<String, Integer, Bitmap> {  private static final String TAG = "ImageLoader";  @Override  protected void onPreExecute() {      // Initialize progress and image      mGetImage.setEnabled(false);      mAbort.setEnabled(true);      mProgressBar.setVisibility(View.VISIBLE);      mProgressBar.setProgress(0);      mImageView.setImageResource(R.drawable.icon);  }  @Override  protected Bitmap doInBackground(String... url) {      /*       * Fucking ridiculous thing happened here, to use any Internet connections, either via HttpURLConnection       * or HttpClient, you must declare INTERNET permission in AndroidManifest.xml. Otherwise you will get       * "UnknownHostException" when connecting or other tcp/ip/http exceptions rather than "SecurityException"       * which tells you need to declare INTERNET permission.       */      try {   URL u;   HttpURLConnection conn = null;   InputStream in = null;   OutputStream out = null;   final String filename = "local_temp_image";   try {       u = new URL(url[0]);       conn = (HttpURLConnection) u.openConnection();       conn.setDoInput(true);       conn.setDoOutput(false);       conn.setConnectTimeout(20 * 1000);       in = conn.getInputStream();       out = openFileOutput(filename, Context.MODE_PRIVATE);       byte[] buf = new byte[8196];       int seg = 0;       final long total = conn.getContentLength();       long current = 0;       /*        * Without checking isCancelled(), the loop continues until reading whole image done, i.e. the progress        * continues go up to 100. But onPostExecute() will not be called.        * By checking isCancelled(), we can stop immediately, i.e. progress stops immediately when cancel() is called.        */       while (!isCancelled() && (seg = in.read(buf)) != -1) {    out.write(buf, 0, seg);    current += seg;    int progress = (int) ((float) current / (float) total * 100f);    publishProgress(progress);    SystemClock.sleep(1000);       }   } finally {       if (conn != null) {    conn.disconnect();       }       if (in != null) {    in.close();       }       if (out != null) {    out.close();       }   }   return BitmapFactory.decodeFile(getFileStreamPath(filename).getAbsolutePath());      } catch (MalformedURLException e) {   e.printStackTrace();      } catch (IOException e) {   e.printStackTrace();      }      return null;  }  @Override  protected void onProgressUpdate(Integer... progress) {      mProgressBar.setProgress(progress[0]);  }  @Override  protected void onPostExecute(Bitmap image) {      if (image != null) {   mImageView.setImageBitmap(image);      }      mProgressBar.setProgress(100);      mProgressBar.setVisibility(View.GONE);      mAbort.setEnabled(false);  }     } }