Passing arguments to AsyncTask and returning results

Question

I have an application that does some long calculations  and I would like to show a progress dialog while this is done  So far I have found that I could do this with threads handlers  but didn t work  and then I found out about the AsyncTask    In my application I use maps with markers on it  and I have implemented the onTap function to call a method that I have defined  The method creates a dialog with Yes No buttons  and I would like to call an AsyncTask if Yes is clicked  My question is how to pass an ArrayList lt String gt  to the AsyncTask  and work with it there   and how to get back a new ArrayList lt String gt  like a result from the AsyncTask   The code of the method looks like this   String curloc   current toString    String itemdesc   item mDescription   ArrayList lt String gt  passing   new ArrayList lt String gt     passing add itemdesc   passing add curloc    ArrayList lt String gt  result   new ArrayList lt String gt      new calc stanica   execute passing result    String minim   result get 0   int min   Integer parseInt minim    String glons   result get 1   String glats   result get 2    double glon   Double parseDouble glons   double glat   Double parseDouble glats    GeoPoint g   new GeoPoint glon  glat   String korisni linii   result get 3     So  as you see  I would like to send the string array list  passing  to the AsyncTask  and to get the  result  string array list back from it  And the calc stanica AssycTask class looks like this   public class calc stanica extends AsyncTask lt ArrayList lt String gt   Void  ArrayList lt String gt  gt        ProgressDialog dialog        Override     protected void onPreExecute             dialog   new ProgressDialog baraj mapa this           dialog setTitle  Calculating               dialog setMessage  Please wait               dialog setIndeterminate true           dialog show               protected ArrayList lt String gt  doInBackground ArrayList lt String gt     passing               Some calculations             return something                   protected void onPostExecute Void unused            dialog dismiss            So my question is how to get the elements of the  passing  array list in the AsyncTask doInBackground method  and use them there   and how to return an array list to use in the main method  the  result  array list

User · Answer

I sort of agree with leander on this one.

call:

new calc_stanica().execute(stringList.toArray(new String[stringList.size()]));

task:

public class calc_stanica extends AsyncTask<String, Void, ArrayList<String>> {
        @Override
        protected ArrayList<String> doInBackground(String... args) {
           ...
        }

        @Override
        protected void onPostExecute(ArrayList<String> result) {
           ... //do something with the result list here
        }
}

Or you could just make the result list a class parameter and replace the ArrayList with a boolean (success/failure);

public class calc_stanica extends AsyncTask<String, Void, Boolean> {
        private List<String> resultList;

        @Override
        protected boolean doInBackground(String... args) {
           ...
        }

        @Override
        protected void onPostExecute(boolean success) {
           ... //if successfull, do something with the result list here
        }
}

User · Answer

I dont do it like this   I find it easier to overload the constructor of the asychtask class     public class calc stanica extends AsyncTask   String String mWhateveryouwantToPass    public calc stanica  String whateveryouwantToPass         this String mWhateveryouwantToPass   String whateveryouwantToPass      Now you can use  whateveryouwantToPass in the entire asynchTask     you could pass in a context to your activity and try that too

User · Answer

You can receive returning results like that  AsyncTask class     Override protected Boolean doInBackground Void    params        if  host isEmpty      dbName isEmpty      user isEmpty      pass isEmpty      port isEmpty              try               throw new SQLException  Database credentials missing              catch  SQLException e                e printStackTrace                         try           Class forName  org postgresql Driver          catch  ClassNotFoundException e            e printStackTrace               try           this conn   DriverManager getConnection this host         this port         this dbName  this user  this pass         catch  SQLException e            e printStackTrace               return true      receiving class    store execute    boolean result   store get      Hoping it will help

User · Answer

Why would you pass an ArrayList   It should be possible to just call execute with the params directly   String curloc   current toString    String itemdesc   item mDescription  new calc stanica   execute itemdesc  curloc    That how varrargs work  right  Making an ArrayList to pass the variable is double work

User · Answer

Change your method to look like this   String curloc   current toString    String itemdesc   item mDescription  ArrayList lt String gt  passing   new ArrayList lt String gt     passing add itemdesc   passing add curloc   new calc stanica   execute passing     no need to pass in result list   And change your async task implementation  public class calc stanica extends AsyncTask lt ArrayList lt String gt   Void  ArrayList lt String gt  gt    ProgressDialog dialog        Override     protected void onPreExecute             dialog   new ProgressDialog baraj mapa this           dialog setTitle  Calculating               dialog setMessage  Please wait               dialog setIndeterminate true           dialog show               protected ArrayList lt String gt  doInBackground ArrayList lt String gt     passing            ArrayList lt String gt  result   new ArrayList lt String gt             ArrayList lt String gt  passed   passing 0     get passed arraylist            Some calculations             return result    return result            protected void onPostExecute ArrayList lt String gt  result            dialog dismiss            String minim   result get 0           int min   Integer parseInt minim           String glons   result get 1           String glats   result get 2           double glon   Double parseDouble glons           double glat   Double parseDouble glats           GeoPoint g   new GeoPoint glon  glat           String korisni linii   result get 3           UPD   If you want to have access to the task starting context  the easiest way would be to override onPostExecute in place   new calc stanica         protected void onPostExecute ArrayList lt String gt  result             here you have access to the context in which execute was called in first place            You ll have to mark all the local variables final though            execute passing

[android] Passing arguments to AsyncTask, and returning results

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