Question

How do i make sure that the async tasks finishes before i run certain tasks. I need to use a variable AFTER the async tasks changes the value of that variable. If i run the code before async is done running then im screwed. any help? im obviously new to async tasks. If you look at my code im probably not using onPostExecute() as it was intended so advice would be helpful. My initial thought was to keep adding things to the async task but im thinking that this is just bad practice since i have tons of things that must be run in series. Basically, what i think it boils down to is: how do i make sure that the tasks in the UI thread dont start to run before my async task has finished.

public class MainActivity extends MapActivity {
myJSONmap;

public void onCreate(Bundle savedInstanceState) {
new AsyncStuff().execute();
locatePlace(myJSONmap);

 class AsyncStuff extends AsyncTask<Void, Integer, JSONObject> {
            @Override
            protected JSONObject doInBackground(Void... params) {
                jObject = GooglePlacesStuff.getTheJSON(formatedURL);
                return null;
            }
            @Override
            protected void onPostExecute(JSONObject result) {
                // TODO Auto-generated method stub
                super.onPostExecute(result);
                myJSONmap = JSONextractor.getJSONHMArrayL(jObject);  // getting the parsed data from the JSON object.
                //the arraylist contains a hashmap of all the relevant data from the google website.
            }
        }

Answer 1

You probably want to read more about AsyncTask on Android Developer

http://developer.android.com/intl/es/reference/android/os/AsyncTask.html

About tips, my personal choice is to pass a Boolean to onPostExecute. That way you can evaluate if the doInBackground was succesful, an then figure out what to do (Error message or update the layout).

Keep in mind that in onPostExecute method ideally should only make the screen update, assuming you have the data ok. In your example, why not include the

myJSONmap = JSONextractor.getJSONHMArrayL(jObject);

on the doInBackground? And then call

locatePlace(myJSONmap);

Like this:

class MyAsyncTask extends AsyncTask<Void, Void, Boolean> {
    String errorMsg;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected Integer doInBackground(Void... v) {
        try{
            jObject = GooglePlacesStuff.getTheJSON(formatedURL);
            myJSONmap = JSONextractor.getJSONHMArrayL(jObject);
            //do stuff
            return true;
        } catch (JSONException e){
            errorMsg="Something wrong in the json";
            return false;
        }

    }

    @Override
    protected void onPostExecute(Boolean success) {
        if(success){
            locatePlace(myJSONmap);
            //update layout
        } else {
            //show error
        }


    }
}