Question

I am fetching JSON from URL using AsycTask, parsing it and displaying the data onto the listView. I also click the refresh button to once again fetch the JSON from URL for some updating. When i click the refresh button the following takes place;
1) adapter.clear() : clearing the listView’s adapter to populate the new data.
2) Fetch JSON from url, parse and display the newly fetched data onto the listView.
3) Meanwhile when fetching the data, I show a progress dialog.

But when i click on the refresh button, the main UI thread freezes during the execution of AsynTask. I mean the refresh button looks pressed until the AsynTask finishes the job as shown below.

Here is my code:

public class AndroidJSONParsingActivity extends SherlockActivity {

    // JSON Node names
    ArrayList<HashMap<String, String>> placeList = new ArrayList<HashMap<String, String>>();
    private static final String TAG_PLACES = "places";
    private static final String TAG_PLACE_NAME = "name";
    private static final String TAG_PLACE_CATEGORY = "category";
    private static final String TAG_PLACE_DISTANCE = "distance";
    private static final String TAG_TRAVEL_TIME = "travel_time";
    ListAdapter adapter;
    public static Context con;
    JSONArray places = null;
    ListView list;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        con = this;
        list = (ListView) findViewById(R.id.listView1);
        parseJSON();

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater inflater = getSupportMenuInflater();
        inflater.inflate(R.menu.activity_main, menu);

        MenuItem menu_item1 = menu.findItem(R.id.menu_item1);

        menu_item1.setOnMenuItemClickListener(new OnMenuItemClickListener() {

            @Override
            public boolean onMenuItemClick(MenuItem item) {
                Toast.makeText(getApplicationContext(), "refresh",
                        Toast.LENGTH_LONG).show();
                placeList.clear();
                parseJSON();
                return false;
            }
        });

        return true;

    }

    public void parseJSON() {
        try {
            placeList = new JSONParsingTask().execute().get();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        adapter = new SimpleAdapter(this, placeList, R.layout.list_item,
                new String[] { TAG_PLACE_NAME, TAG_PLACE_CATEGORY,
                        TAG_PLACE_DISTANCE, TAG_TRAVEL_TIME }, new int[] {
                        R.id.name, R.id.category, R.id.distance,
                        R.id.travel_time });

        list.setAdapter(adapter);

        list.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                String name = ((TextView) view.findViewById(R.id.name))
                        .getText().toString();
                String category = ((TextView) view.findViewById(R.id.category))
                        .getText().toString();
                String distance = ((TextView) view.findViewById(R.id.distance))
                        .getText().toString();
                String travel_time = ((TextView) view
                        .findViewById(R.id.travel_time)).getText().toString();

                Intent in = new Intent(getApplicationContext(),
                        SingleMenuItemActivity.class);
                in.putExtra(TAG_PLACE_NAME, name);
                in.putExtra(TAG_PLACE_CATEGORY, category);
                in.putExtra(TAG_PLACE_DISTANCE, distance);
                in.putExtra(TAG_TRAVEL_TIME, travel_time);
                startActivity(in);

            }
        });

    }

}

class JSONParsingTask extends
        AsyncTask<Void, Void, ArrayList<HashMap<String, String>>> {
    public Boolean flag = false;
    private static String url = "http://some - url";

    // JSON Node names

    private static final String TAG_PLACES = "places";
    private static final String TAG_PLACE_NAME = "name";
    private static final String TAG_PLACE_CATEGORY = "category";
    private static final String TAG_PLACE_DISTANCE = "distance";
    private static final String TAG_TRAVEL_TIME = "travel_time";
    ListAdapter adapter;
    JSONParser jParser;
    ListView list;
    static ArrayList<HashMap<String, String>> placeList = new ArrayList<HashMap<String, String>>();
    JSONArray places = null;

    ProgressDialog JSONParsingDialog = new ProgressDialog(
            AndroidJSONParsingActivity.con);

    @Override
    protected void onPreExecute() {
        JSONParsingDialog.setMessage("Preparing data...");
        JSONParsingDialog.setCanceledOnTouchOutside(false);
        JSONParsingDialog.setCancelable(false);
        JSONParsingDialog.show();
    }

    @Override
    protected ArrayList<HashMap<String, String>> doInBackground(Void... params) {
        JSONParser jParser = new JSONParser();

        final JSONObject json = jParser.getJSONFromUrl(url);

        try {
            places = json.getJSONArray(TAG_PLACES);

            for (int i = 0; i < places.length(); i++) {
                JSONObject c = places.getJSONObject(i);

                String name = c.getString(TAG_PLACE_NAME);
                String category = c.getString(TAG_PLACE_CATEGORY);
                String distance = c.getString(TAG_PLACE_DISTANCE);
                String travel_time = c.getString(TAG_TRAVEL_TIME);

                HashMap<String, String> map = new HashMap<String, String>();

                map.put(TAG_PLACE_NAME, name);
                map.put(TAG_PLACE_CATEGORY, category);
                map.put(TAG_PLACE_DISTANCE, distance);
                map.put(TAG_TRAVEL_TIME, travel_time);

                placeList.add(map);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return placeList;
    }

    @Override
    protected void onPostExecute(ArrayList<HashMap<String, String>> result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        JSONParsingDialog.dismiss();
    }

}

All i need is, when i click on the refresh button, it should be smooth and should not freeze until the AsynTask is completed. Any idea how can i do this?

Answer 1

use

new JSONParsingTask().execute(); 

.get() blocks the caller thread.

more info: Looking for good example of using get() with an AsyncTask in android