Adding an AsyncTask - Android

Question

I'm trying to add an AsyncTask to the following class but I'm not sure where to start. I would like to encapsulate the entire class if possible. I'm new to Android and Java so I really have no idea about what I'm doing. The following class works, and I can send all the information to my database properly. Each time the user's location is updated, the program first checks a table in the database for the user ID; if it does not exist in the table the GPS coordinates are sent, but if the user ID is in the table, the coordinates are not sent and the program stops sending location updates. This works like it should, but it locks up my UI and throws an ANR error when attempting to interact. I know that I need to implement an AsyncTask, but I need some guidance. Below is the complete code for the class. Any help would be great!

public class FindLocation  {

protected static final Context SendLocation = null;
private LocationManager locManager;
private LocationListener locListener;

Context ctx;

public FindLocation(Context ctx) {
     this.ctx = ctx;
}
public void startLocation(final Context context, String usr_id2) { 

    final String usr = usr_id2;

    //get a reference to the LocationManager
    locManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);

    //checked to receive updates from the position
    locListener = new LocationListener() {
        public void onLocationChanged(Location loc) {

            String lat = String.valueOf(loc.getLatitude()); 
            String lon = String.valueOf(loc.getLongitude());

            JSONArray jArray;
            String result = null;
            InputStream is = null;
            StringBuilder sb = null;

             ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
             nameValuePairs.add(new BasicNameValuePair("id", usr));

            //http post
            try{

                 HttpClient httpclient = new DefaultHttpClient();
                 HttpPost httppost = new HttpPost("http://www.example.com/test/example.php");     
                 httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
                 HttpResponse response = httpclient.execute(httppost);
                 HttpEntity entity = response.getEntity();
                 is = entity.getContent();
                 }catch(Exception e){
                     Log.e("log_tag", "Error in http connection"+e.toString());
                }

            //convert response to string
            try{
                  BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
                   sb = new StringBuilder();
                   sb.append(reader.readLine() + "\n");

                   String line="0";
                   while ((line = reader.readLine()) != null) {
                                  sb.append(line + "\n");
                    }
                    is.close();
                    result=sb.toString();
                    }

                    catch(Exception e){
                          Log.e("log_tag", "Error converting result "+e.toString());                    
                    }
            try{
                  jArray = new JSONArray(result);
                  JSONObject json_data=null;
                  for(int i=0;i<jArray.length();i++){
                         json_data = jArray.getJSONObject(i);
                         String ct_name = json_data.getString("phoneID");
                         if(ct_name == usr) {
                             locManager.removeUpdates(locListener);
                         }
                     } 
                  }

                  catch(Exception e){
                        HttpClient httpclient = new DefaultHttpClient();
                        HttpPost httppost = new HttpPost("http://example.com/test/example.php");

                        try {
                               List<NameValuePair> nameValuePairs1 = new ArrayList<NameValuePair>(2);
                               nameValuePairs1.add(new BasicNameValuePair("lat", lat)); 
                               nameValuePairs1.add(new BasicNameValuePair("lon", lon));
                               nameValuePairs1.add(new BasicNameValuePair("id", usr));
                               httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs1));
                               httpclient.execute(httppost);
                         } 
                         catch (ClientProtocolException g) {
                             // TODO Auto-generated catch block
                         } catch (IOException f) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        } 
            } 
        }       


        public void onProviderDisabled(String provider){
        }
        public void onProviderEnabled(String provider){ 
        }
        public void onStatusChanged(String provider, int status, Bundle extras){
        }
    };
    locManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 6000, 0, locListener);
}
}

Answer 1

All you should have to do is:

• modify FindLocation class by extending asynctask
• change startLocation for an override of doInBackground.

Then call the execute method of your asynctask instead of startLocation.

Also, in your case, an asynctask may not be the best. Usually you use an asynctask because you want to do something in the background and then, when the task is done, update some ui components with the result of the background operation. Here, as you just want something in the background but no UI update, you could be better using a normal thread :

• make you class extend thread
• change startLocation for an override of run
• start your thread instead of calling startLocation

--Update with details --

This could be simpler but the idea to get more familiar with asyncTask ia a good one too.

public class LocationFinder extends Thread {

  public LocationFinder( Context ctx ) {
   this.ctx = ctx;
  }

  public void start( String userId ) {
    this.userId = userId;
    super.start();
  }

  //defensive programming : prevent your thread from beeing started in an undesired way
  @Override 
  public void start() {
    throw new IllegalStateException( "LocationFinder can't be started using start(). Prefer start( int )." );
  }

  public void run() {
    //remaining of the code of startLocation except the first line.
  }

}

to use your thread then do in an activity :

new LocationFinder( this ).start( userId );

Answer 2

 private class BackgroundLoader extends AsyncTask<Void, Void, Void> {
 private ProgressDialog dialog;
 protected Long doInBackground() {
    dialog = new ProgressDialog(ctx);
    dialog.show();
 }

 protected void doInBackground() {
     // do all your stuff here that doesn't modify the UI
 }

 protected void onPostExecute(Long result) {
    // do what you need to to the UI
    dialog.dismiss();
 }

Then to create an instance call new BackgroundLoader().execute(); in your onCreate() method