How one interface can be used for different background android tasks?

The most simplistic solution I can think of is to modify your DelegateTaskCompleted interface so as it looks like this:

public interface DelegateTaskCompleted{
  public void JsonArrayLoaded(AsyncTask<String, String, String> task, 
                              JSONArray result);
}

Then your onPostExecute will send itself back like below:

protected void onPostExecute(String file_url)   
{           
    pDialog.dismiss();      
    delegate.JsonArrayLoaded(this, gotNearestbeacons);
}

Finally, in your MainClass, you can have a conditional check based on the type of AsyncTask:

 @Override
 public void JsonArrayLoaded(AsyncTask<String, String, String> task,
                             JSONArray result) 
    {
         if(task instanceof GettingBeaconsList) { 
                //  do stuff related to the beacon list
         }

         else if(task instanceof GettingAirports) { 
            // do airport list stuff
         }

    }

That way you can easily identify the AsyncTask that sends through the response without having to track which it is, if one takes longer than the other etc.

---

Alternatively, have another class that extends AsyncTask but adds an abstract variable for identification.

public class TrackableAsyncTask extends AsyncTask<String, String, String>{
    public abstract int getId();

    public static final int ID_AIRPORT = 1;
    public static final int ID_BEACONS = 2;
    ... etc
}

Then have your Airport and Beacon AsycTasks extend this instead. This will require them to implement the getId method.

public class GettingAirports extends AsyncTask<String, String, String> {
     public int getId(){
        return ID_AIRPORT;
     }
}

And then instead of doing a conditional if (task instanceof GettingAirports) you can do a switch statement like below:

switch(task.getId()){
   case TrackableAsyncTask.ID_AIRPORT:
       // run airport code
}

Hope this helps.

You can also consider Handler to achieve this. Create handler in Activity, Pass this handler object to each AsyncTask. In onPost call handler.sendEmptyMessage(CONSTANT_INT); In Handler handleMessage check msg.what in if or switch This way only one object of handler will be created and used within multiple calls for async from one activity

This is the interface for callback

public interface CallbackReceiver {
    public void receiveData(Object result);

}

Use Asynctask class as Abstract class

public abstract class JsonDataCallback extends AsyncTask<String, String, String> implements CallbackReceiver {
private ProgressDialog mProgressDialog;
Handler handler;
Runnable callback;
Activity activity;


public JsonDataCallback(Activity activity) 
{
     this.activity=activity;
     mProgressDialog = new ProgressDialog(activity);
     mProgressDialog.setMessage("Loading Please Wait.");
     mProgressDialog.setIndeterminate(false);
     mProgressDialog.setMax(100);
     mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
     mProgressDialog.setCancelable(true);
}

public abstract void receiveData(Object object);
@Override
protected void onPreExecute() {
    mProgressDialog =ProgressDialog.show(activity, "", "Please Wait",true,false);
    super.onPreExecute();
}

@Override
protected String doInBackground(String... aurl) {
    String results="";
    // do stuff
    return results;
}


@Override
protected void onPostExecute(String jsonData) {
     if (mProgressDialog != null || mProgressDialog.isShowing()){
         mProgressDialog.dismiss();
 }
     if(jsonData!=null)
     {
         receiveData(jsonData);
     }
}
}

And in your code use it like this

String url = ipaddress + "/GrantAdvanceList;
            JsonDataCallback callbackservice = new JsonDataCallback(yourActivity.this) {
                @Override
                public void receiveData(Object object) {
                    jsonRecordsData = (String)object;
                    //do stuff with call back data
                }
            };

        callbackservice.execute(url, null, null);

You can reuse the code this way.