Screen freezes when downloading content from server in android

Question

I am downloading JSON Content from server in the MainActivity and passing the JSON from MainActivity to ListActivity, the problem here is I have added a sleep time of 10s in the backend server ie Php from where the data is fetched. Since, the response will the delayed I would expect that screen opens and waits until the response comes and move to next screen. But what is happening is the screen goes white/black completely untill the response is recieved and ListActivity is loaded, the problem here is the MainActivity is never visible. Below is code for the same:

MainActivity

JSONData jsonData = new JSONData();
String jsonList = jsonData.fetchList();

Intent intent = new Intent(getApplicationContext(),ListActivity.class);
intent.putExtra("jsonList",jsonList);
startActivity(intent);
finish();

JSON Data class

public String fetchList() {
        try {
            String list = new DownloadJSONData().execute(listURL).get().toString();
            return list;
        } catch (Exception e) {
            return "";
        }
    }

private class DownloadJSONData extends AsyncTask<String, String, String> {
        protected void onPreExecute() {
            super.onPreExecute();
        }

        protected String doInBackground(String... params) {

            HttpURLConnection connection = null;
            BufferedReader reader = null;
            try {
                URL url = new URL(params[0]);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                InputStream stream = connection.getInputStream();
                reader = new BufferedReader(new InputStreamReader(stream));
                StringBuffer buffer = new StringBuffer();
                String line;
                while ((line = reader.readLine()) != null) {
                    buffer.append(line + "\n");
                }
                return buffer.toString();
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                if (connection != null) {
                    connection.disconnect();
                }
                try {
                    if (reader != null) {
                        reader.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return "";
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
        }
    }

Answer 1

you are using get() method which accquires the main thread or ui thread untill the async task is completed

you should avoid using get() and also can use progress dialog in onPreExecute for displaying progression on network call to user