AsyncTask instance in Android

Mainactivity is as follows:

Package com. example. asynctasktest; 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. app. activity; import android. OS. asyncTask; imp Ort android. OS. bundle; import android. view. view; import android. view. view. onClickListener; import android. widget. button; import android. widget. progressBar; import android. widget. textView; import android. widget. toast; public class MainActivity extends Activity {private Button satrtButton; private Button cancelButton; private ProgressBar progressBar; private TextView textView; private DownLoaderAsyncTask downL OaderAsyncTask; @ Override public void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. main); initView ();} public void initView () {satrtButton = (Button) findViewById (R. id. startButton); cancelButton = (Button) findViewById (R. id. cancelButton); satrtButton. setOnClickListener (new ButtonOnClickListener (); cancelButton. setOnClickListener (new ButtonOnClickListe Ner (); progressBar = (ProgressBar) findViewById (R. id. progressBar); textView = (TextView) findViewById (R. id. textView);} private class ButtonOnClickListener implements OnClickListener {public void onClick (View v) {switch (v. getId () {case R. id. startButton: // Note: // 1 each time a new instance is required, the new task can only be executed once, otherwise, an exception may occur. The // 2 asynchronous task instance must be created in the UI thread. The // 3 execute () method must be called in the UI thread. DownLoaderAsyncTask = new downloaderasynctask(downloaderasynctask.exe cute ("http://www.baidu.com"); break; case R. id. cancelButton: // cancel an ongoing task. The onCancelled () method will be called downLoaderAsyncTask. cancel (true); break; default: break ;}}// constructor AsyncTask <Params, Progress, Result> parameter description: // input parameter of Params startup task execution // Progress of the Progress background task execution // type of Result background calculation Result private class DownLoaderAsyncTask extends AsyncTask <String, Integer, Stri Ng> {// The onPreExecute () method is used to prepare the main thread for executing an asynchronous task @ Overrideprotected void onPreExecute () {super. onPreExecute (); textView. setText ("Call onPreExecute () method ---> prepare to start executing asynchronous tasks"); System. out. println ("Call onPreExecute () method ---> prepare to start executing asynchronous tasks");} // The doInBackground () method is used to execute asynchronous tasks, you cannot change the UI @ Overrideprotected String doInBackground (String... params) {System. out. println ("Call doInBackground () method ---> start to execute asynchronous task"); try {HttpClient client = new DefaultHttpClient (); HttpGet get = new HttpGet (params [0]); HttpResponse response = client.exe cute (get); if (response. getStatusLine (). getStatusCode () = HttpStatus. SC _ OK) {HttpEntity entity = response. getEntity (); InputStream is = entity. getContent (); long total = entity. getContentLength (); ByteArrayOutputStream bos = new ByteArrayOutputStream (); byte [] buffer = new byte [1024]; int count = 0; int length = -1; while (length = is. read (buffer ))! =-1) {bos. write (buffer, 0, length); count + = length; // publishProgress () is a method in the AsyncTask class // usually in doInBackground () to notify the main thread about the execution of background tasks. // at this time, the onProgressUpdate () method publishProgress (int) (count/(float) total) * 100) in AsyncTask will be triggered; // to demonstrate the progress, sleep 1000 ms Thread. sleep (1000);} return new String (bos. toByteArray (), "UTF-8") ;}} catch (Exception e) {return null;} // After the onPostExecute () method is used for asynchronous task execution, the operation @ Overrideprotected void onPostExecute (String result) {super. onPostExecute (result); Toast. makeText (getApplicationContext (), "Call onPostExecute () method ---> asynchronous task execution completed", 0 ). show (); // textView displays the network request result textView. setText (result); System. out. println ("calling onPostExecute () method ---> asynchronous task execution completed");} // onProgressUpdate () method is used to update asynchronous execution, process the execution information of asynchronous tasks in the main thread @ Overrideprotected void onProgressUpdate (Integer... values) {super. onProgressUpdate (values); // modify the progress bar. setProgress (values [0]); // modify TextViewtextView. setText ("loaded" + values [0] + "%");} // The onCancelled () method is used when an asynchronous task is canceled, execute related operations in the main thread @ Overrideprotected void onCancelled () {super. onCancelled (); // change the progress bar to 0progressBar. setProgress (0); // modify TextViewtextView. setText ("Call onCancelled () method ---> asynchronous task canceled"); System. out. println ("calling onCancelled () method ---> asynchronous task canceled ");}}}

Main. XML is as follows:

<LinearLayout xmlns: android = "http://schemas.android.com/apk/res/android" xmlns: tools = "http://schemas.android.com/tools" android: layout_width = "match_parent" android: layout_height = "match_parent" android: orientation = "vertical"> <Button android: id = "@ + id/startButton" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "Start asynchronous task"/> <Button android: id = "@ + id/cancelButton" Ndroid: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "cancel asynchronous task"/> <ProgressBar android: id = "@ + id/progressBar" style = "? Android: attr/progressBarStyleHorizontal "android: layout_width =" fill_parent "android: layout_height =" wrap_content "android: max =" 100 "android: progress =" 0 "/> <ScrollView android: id = "@ + id/scrollView" android: layout_width = "fill_parent" android: layout_height = "wrap_content"> <TextView android: id = "@ + id/textView" android: layout_width = "fill_parent" android: layout_height = "wrap_content" android: text = "test"/> </ScrollView> </LinearLayout>

Important references:

Http://blog.csdn.net/liuhe688/article/details/6532519

Thank you very much