Showing progress bar while loading a List

Question

Ok Now i admit that i am new to using progress bar infact i never use it but now i need to use it I have an activity (Main) and a menu which can start 6 new activity. From these activities there is an activity which load the data in a ListView it take 3-4 second to load .This activity parse the json and pass the data to another activity. How can i show the progress bar as soon as user click the menu option for this activity and disappear it when List will be loaded.

Here is the activiy

    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
     final Intent intent=new Intent(this ,GetLatAndLng.class);
    setContentView(R.layout.listplaceholder);
    //ProgressBar pb=(ProgressBar)findViewById(R.id.progressbar);
    LocationManager locationManager;
    String context=Context.LOCATION_SERVICE;
    locationManager=(LocationManager)getSystemService(context);

    Criteria criteria = new Criteria();
    criteria.setAccuracy(Criteria.ACCURACY_FINE);
    criteria.setAltitudeRequired(false);
    criteria.setBearingRequired(false);
    criteria.setCostAllowed(true);
    criteria.setPowerRequirement(Criteria.POWER_LOW);
    String provider = locationManager.getBestProvider(criteria, true);
    Location location = locationManager.getLastKnownLocation(provider);

    final LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(Location location) {
        updateWithNewLocation(location);
        }
        public void onProviderDisabled(String provider){
        updateWithNewLocation(null);
        }
        public void onProviderEnabled(String provider){ }
        public void onStatusChanged(String provider, int status,
        Bundle extras){ }
        };
    updateWithNewLocation(location);
    locationManager.requestLocationUpdates(provider, 2000, 10,
            locationListener);
    double geoLat = location.getLatitute();
    double geoLng = location.getLongitude();
         Bundle b=new Bundle();
    //pb.setVisibility(View.VISIBLE);
    ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();

    JSONObject json = JSONFunction.getJSONfromURL(getUrl());
    Log.v(TAG, "got the json"); 
    try{
        JSONArray  JArray = json.getJSONArray("results");
           Log.v(TAG, "getting results");
        for(int i=0;i<JArray.length();i++){                     
            HashMap<String, String> map = new HashMap<String, String>();    
            JSONObject e = JArray.getJSONObject(i);
            JSONObject location1=e.getJSONObject("geometry").getJSONObject("location");
            latitude[i]=location1.getDouble("lat");
            longitude[i]=location1.getDouble("lng");
            reference[i]=e.getString("reference");
            Log.v(TAG, reference[i]);
            distance[i]=GetLatAndLng.gps2m(geoLat, geoLng,latitude[i] ,longitude[i]); 
            map.put("id",  String.valueOf(i));
            map.put("name", "" + e.getString("name"));
            map.put("vicinity", "Address " +  e.getString("vicinity")+" "+"Disance:"+distance[i]);

            mylist.add(map);                
        }           
    }catch(JSONException e)        {
         Log.e("log_tag", "Error parsing data "+e.toString());
    }
//   pb.setVisibility(View.GONE);
    b.putStringArray("key", reference);
    intent.putExtras(b);
    Log.v(TAG, ""+reference); 
    ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.listview, 
                    new String[] { "name", "vicinity", }, 
                    new int[] { R.id.item_title, R.id.item_subtitle });

    setListAdapter(adapter);
    final ListView lv = getListView();
    lv.setTextFilterEnabled(true);  
    lv.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {        
            @SuppressWarnings("unchecked")
            HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);                   
           Toast.makeText(JsonExampleActivity.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show();
            intent.putExtra("clickedid",position);
            startActivity(intent);
        }
    });
}
public void updateWithNewLocation(Location location2) {
    if(location2!=null) {
          double geoLat = location2.getLatitude();
            double geoLng = location2.getLongitude();
    }
}

Thanks in Advance!!

Answer 1

Use AsyncTask to load data in background while showing loading indicator. In AsyncTask's doInBackground method , process the JSON or anything which is taking time.

public class HeavyWorker extends AsyncTask < String , Context , Void > {

    private ProgressDialog      progressDialog ;
    private Context             targetCtx ;

    public HeavyWorker ( Context context ) {
        this.targetCtx = context ;
        this.needToShow = true;
        progressDialog = new ProgressDialog ( targetCtx ) ;
        progressDialog.setCancelable ( false ) ;
        progressDialog.setMessage ( "Retrieving data..." ) ;
        progressDialog.setTitle ( "Please wait" ) ;
        progressDialog.setIndeterminate ( true ) ;
    }

    @ Override
    protected void onPreExecute ( ) {
        progressDialog.show ( ) ;
    }

    @ Override
    protected Void doInBackground ( String ... params ) {
      // Do Your WORK here

       return null ;
    }

    @ Override
    protected void onPostExecute ( Void result ) {
        if(progressDialog != null && progressDialog.isShowing()){
            progressDialog.dismiss ( ) ;
        }
    }
}

In your Activity's onCreate() execute AsyncTask

new HeavyWorker().execute();