Android Doing something AFTER Activity is visible

Question

I have activity with a button.When button is clicked,a new activity starts and in this activity , various data fetch from web.But when I click the button , first activity holds on for a while and after 3-4 seconds second activity starts with ready datas.Apparently,before second activity is visible,app tries to fetch data.But firstly,I want second activity is visible to user, after that fetching data must start. I examined activity lifecycle and replaced fetching to onStart() but not working

 @Override
 protected void onStart() {
          super.onStart();
          //Fetch data
 }

How can I do that ?

Here is my all code (just second activity) :

public class GuzergahActivity extends android.support.v4.app.FragmentActivity{

      private GoogleMap map;
      private GuzergahOverlay overlay;
      private WebView webview;
      private ImageView imageview;
      private ProgressDialog dialog;
      private int flag;

      @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        overridePendingTransition(0, 0);
        setContentView(R.layout.guzergah);
        flag=this.getIntent().getExtras().getInt("flag");
        setUpMapIfNeeded();
        setUpView();
      }

      @Override
      protected void onResume() {
          super.onResume();
          setUpMapIfNeeded();
      }

      @Override 
      protected void onDestroy() {
        if (dialog!=null) {
            dialog.dismiss();
        }
        super.onDestroy();
      }

      private void setUpMapIfNeeded() {
            // Do a null check to confirm that we have not already instantiated the map.
            if (map == null) {
                map = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.guzergah_fragment)).getMap();
                if(map!=null){
                    setUpMap();
                }
            }
      }

    private void setUpMap(){

         try {
            String result=new MyNewTask().execute().get();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
         overlay.setOverlay(map);
         map.moveCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(39.910526,32.804435),15));
         map.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null);
    }


    private void setUpView() {
           //Binding imageview,webview...and setting up their features
    }

    private class MyNewTask extends AsyncTask<String,Integer,String> 
    {
        @Override
        protected void onPreExecute()
        {

            dialog= new ProgressDialog(GuzergahActivity.this);
            dialog.setIndeterminate(true);
            dialog.setCancelable(false);
            dialog.setMessage("Downloading! Please wait...!");
            dialog.show();

        }


        @Override
        protected String doInBackground(String... params)
        {
            /* Fetching data is in this class - GuzergahOverlay*/ 
            overlay =  new GuzergahOverlay(flag);

            return "Done";

      }

        @Override
        protected void onPostExecute(String result) 
        {
            super.onPostExecute(result);
            Log.i("result","" +result);
            if(result!=null){
                dialog.dismiss();
            }
        }

    } //end MyNewTask
}



public class GuzergahOverlay {

private MarkerOptions beytepe_kampusu;
private MarkerOptions sihhiye_kampusu;
private ArrayList<PolylineOptions> lines;
private ArrayList<MarkerOptions> stops;

public GuzergahOverlay(int mode) {
    beytepe_kampusu=new MarkerOptions().position(new LatLng(39.87159,32.735435)).title("Hacettepe Üniversitesi Beytepe Yerleşkesi").icon(BitmapDescriptorFactory.fromResource(R.drawable.marker_beytepe));
    sihhiye_kampusu=new MarkerOptions().position(new LatLng(39.931599,32.862365)).title("Hacettepe Üniversitesi Sıhhıye Yerleşkesi").icon(BitmapDescriptorFactory.fromResource(R.drawable.marker_sihhiye));
    getLinesAndStops(mode); //Here is fetching geopoint and preparing lines and stops arraylists
}

private void getLinesAndStops(int mode) {

    // Fetching data from Parse.com
            // Fillinp up lines and stops arraylists
}




public void setOverlay(GoogleMap map){
    map.addMarker(beytepe_kampusu);
    map.addMarker(sihhiye_kampusu);
    for(PolylineOptions polyline : lines){
        map.addPolyline(polyline);
    }
    for(MarkerOptions marker : stops){
        map.addMarker(marker);
    }
}
}

With above code , when I click button , first activity holds on for a while and second activity is visible when fetching data finished.Progress dialog is visible for just a few milisecond

Answer 1

Sounds as if you are running all your code in the UI thread. Would be nice with more code to be able to give a better example.

In your second activity:

    private class BackgroundTask extends AsyncTask<Void, Void, Void> {

    // Before running code in separate thread
    @Override
    protected void onPreExecute() {
        // setup loading dialog
    }

    @Override
    protected Void doInBackground(Void... arg0) {
        // do long running code
        return null;
    }

    // after executing the code in the thread
    @Override
    protected void onPostExecute(Void arg) {
        // dismiss your dialog

    }

}

And inside onCreate:

new BackgroundTask().execute();

Edit:

Now that I have seen your code I would suggest you try something like this:

    private void setUpMap(){
        map.moveCamera(CameraUpdateFactory.newLatLngZoom(new      LatLng(39.910526,32.804435),15));
        map.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null);
        new Handler().postDelayed(new Runnable() {
            public void run() {
                try {
                    String result = new MyNewTask().execute();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (ExecutionException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                /*
                 * you should move this call to onPostExecute
                 * then you will not need to call execute().get() 
                 * which takes away the advantage of AsyncTask
                 * as it then is run on UI thread
                 */

                overlay.setOverlay(map);
            }
        }, 2000);

    }

Setting up the map is an UI heavy task, so in my experience it looks nicer to wait a bit before loading markers etc. Furthermore this should enable the dialog to properly show before it is dismissed.

Answer 2

You should move the data fetching method into an AsyncTask. You should never fetch data from a remote source on the UI thread. If you move that operation into a background thread in this way, the UI will have a higher priority, and should load quickly, while still allowing your asynchronous task to complete. You can even start the task in onCreate or onStart, and you should see better performance.