Passing an ArrayList from an asynchronous method

Issue

I currently fetch Json data from a async method (XmlParser.java) and pass that as a String back to a textview, I now need to pass back an ArrayList instead, what do I need to change in the below code for that to work?

BookDetail.java

public class BookDetail extends AppCompatActivity {


public static TextView tvBooks;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_schedule_detail);

            tvBooks = (TextView) findViewById(R.id.tvBooks);

    XmlParser xmlParser = new XmlParser();
    XmlParser.theUrl = "http://pathtoapi.xxxxx/api;
    xmlParser.execute();
}

}

XMLParser.java

public class XmlParser extends AsyncTask<Void,Void,Void> {

String data ="";
String dataParsed = "";
String singleParsed ="";

public static String theUrl;

protected Void doInBackground(Void... voids) {
    try {
        URL url = new URL(theUrl);

        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
        InputStream inputStream = httpURLConnection.getInputStream();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        String line = "";
        while(line != null){
            line = bufferedReader.readLine();
            data = data + line;
        }

        list = new ArrayList<Agenda>();

        JSONArray JA = new JSONArray(data);
        for(int i =0 ;i <JA.length(); i++){
            JSONObject JO = (JSONObject) JA.get(i);

            singleParsed =  "Book: " + JO.get("bookName");
            dataParsed = dataParsed + singleParsed +"\n" ;

        }

    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (JSONException e) {
        e.printStackTrace();
    }

    return null;
}


@Override
protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);
    // Here a TextView is populated with String
    // But I would like to pass an ArrayList instead that can populate a ListView instead
    BookDetail.tvBooks.setText(this.dataParsed);
}   

}

Solution

if you want to return a value from AsyncTask then your AsyncTask definition be must like this:

public class XmlParser extends AsyncTask<Void,Void,ArrayList<Agenda>> {
    protected ArrayList<Agenda> doInBackground(Void... voids) {
         // do background
         return list;
    }

    protected void onPostExecute(ArrayList<Agenda> list) {
    }
}

in AsyncTask template, the first argument is type of passed value to task, the second argument is value that pass to onProgress , and the last argument is for type of return value of doInBackground

and add get method to end of execute statement:

    ArrayList<Agenda> list = xmlParser.execute().get();

Answered By - nariman amani