Handling Return Value from AsyncTask

Issue

I'm trying to display a list of names using an AsyncTask. doInBackground() stores all the names found on a database in a String array.

public class GetAll extends AsyncTask<String, Void, String[]> {

    public String convertStreamToString(InputStream is) {
        java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
        return s.hasNext() ? s.next() : "";
    }

    @Override
    protected String[] doInBackground(String... apikey) {
        String[] Students;
        //Making a http call
        HttpURLConnection urlConnection;
        InputStream in = null;
        try {
            // the url we wish to connect to
            URL url = new URL("http://radikaldesign.co.uk/sandbox/studentapi/getallstudents.php?apikey="+apikey);
            // open the connection to the specified URL
            urlConnection = (HttpURLConnection) url.openConnection();
            // get the response from the server in an input stream
            in = new BufferedInputStream(urlConnection.getInputStream());
        } catch (IOException e) {
            e.printStackTrace();
        }
        // convert the input stream to a string
        String response = convertStreamToString(in);
        // print the response to android monitor/log cat
        System.out.println("Server response = " + response);
        final ArrayList<Student> allStudents= new ArrayList<>();
        try {
            // declare a new json array and pass it the string response from the server
            // this will convert the string into a JSON array which we can the iterate
            // over using a loop
            JSONArray jsonArray = new JSONArray(response);
            // instantiate the cheeseNames array and set the size
            // to the amount of cheese object returned by the server
            Students = new String[jsonArray.length()];

            // use a for loop to iterate over the JSON array
            for (int i=0; i < jsonArray.length(); i++)
            {
                // the following line of code will get the name of the cheese from the
                // current JSON object and store it in a string variable called name
                String name = jsonArray.getJSONObject(i).get("name").toString();
                String gender= jsonArray.getJSONObject(i).get("gender").toString();
                String dob= jsonArray.getJSONObject(i).get("dob").toString();
                String address= jsonArray.getJSONObject(i).get("address").toString();
                String postcode= jsonArray.getJSONObject(i).get("postcode").toString();
                String studentNumber= jsonArray.getJSONObject(i).get("studentNumber").toString();
                String courseTitle= jsonArray.getJSONObject(i).get("courseTitle").toString();
                String startDate= jsonArray.getJSONObject(i).get("startDate").toString();
                String bursary= jsonArray.getJSONObject(i).get("bursary").toString();
                String email= jsonArray.getJSONObject(i).get("email").toString();

                Student s= new Student(name, gender, dob, address, postcode, studentNumber, courseTitle, startDate, bursary, email);
                allStudents.add(s);
                Students[i]= name;
                return Students;
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return new String[0];
    }

Once the array is filled I want to display the results in a ListView on the MainActivity.

I've tried to store the results like using

String[] Students= new GetAll.execute(apikey);

and then use an ArrayAdapter to fill the listview. That did not work so I'm here for help and suggestions. Thanks

Solution

Adding to ADM's answer.. Create a inner class in the activity which extends Async Task which makes populating your original list after thread call simpler.

Call it as: new GetAll().execute("string");

Answered By - Shubham Agarwal Bhewanewala