Adding multiple markers to Google Maps API v2 from List array with the helping of AsyncTask

Question

My app requires adding of hundreds markers (in some cases). For this I am using "for loop" which seems to be not bad solution if I am using default markers. I need to use custom image for each marker which I am downloading from the internet with the helping of AsynkTask class Loader(). But when I am using custom markers the UI freezes until "for loop" will be finished.

Adding markers:

private List<User> mUsers = new ArrayList<User>();
private GoogleMap mMap;
Bitmap bAvatar;

.............

private void drawMarkers() {
        mMap.clear();
        for (User user : mUsers) {
            if (user.getGeohash() != null) {
                LatLng pos = gh.decode(user.getGeohash());
                if (user.getAvatar() != null) {
                    try {
                        bAvatar = new Loader().execute(user.getAvatar()).get();                     
                    } catch (InterruptedException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    } catch (ExecutionException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    }
                    mMap.addMarker(new MarkerOptions()
                            .position(pos)
                            .title(user.getStatus())
                            .icon(BitmapDescriptorFactory.fromBitmap(bAvatar)));
                } else {
                    mMap.addMarker(new MarkerOptions()
                            .position(pos)
                            .title(user.getStatus())
                            .icon(BitmapDescriptorFactory
                                    .defaultMarker(BitmapDescriptorFactory.HUE_RED)));
                }

            }
        }
    }

AsyncTask for image downloading:

public class Loader extends AsyncTask<String, Void, Bitmap> {
    Bitmap bitmap;

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
    }

    protected Bitmap doInBackground(String... urls) {
        String urldisplay = urls[0];
        Bitmap mIcon11 = null;
        try {
            InputStream in = new java.net.URL(urldisplay).openStream();
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inPurgeable = true;
            options.inInputShareable = true;
            mIcon11 = BitmapFactory.decodeStream(in, null, options);
        } catch (Exception e) {
            String error = (e.getMessage() == null) ? "doInBackground - Loader"
                    : e.getMessage();
            Log.e("Error", error);
            e.printStackTrace();
        }
        return mIcon11;
    }

    protected void onPostExecute(Bitmap result) {

        bitmap = result;

    }
}

I assume that I need to replace "for loop" with the AsynkTask where each user from List<User> will be downloaded asynchronously.

Please help me to create AsynkTask for List<User> array.
Should I combine AsynkTask for List<User> with AsynkTask for image downloading or is it correct to use AsynkTask inside AsynkTask ?

Any help will be appreciated. Thanks in advance.

score 0 · Accepted Answer · answered Jul 08 '13 at 22:35

First:

You shouldn't used nested AsyncTasks. That's not supported.
You should however try to combine your image downloads for your users.

Here's what you need to do:

Create an asyntask that loops through your users in the doInBackground method.
In the doInBackground for each user, download the bitmap,
Use the publishProgress method when you've retrieved the bitmap.
Calling publishProgress will trigger the onProgressUpdate method on the UI thread, where you can add your marker to the map.

See the DownloadFilesTask example on the Android developers site.

Adding multiple markers to Google Maps API v2 from List array with the helping of AsyncTask

1 Answers1