Question

I currently have a UI that uses an AsyncTask class to make a web service call. This call gets several pictures and stores them in a HashMap. The UI is then notified and the UI is created with these images. However, this sometimes takes as long as 10 – 15 seconds, which is annoying. Is there a way to populate the UI one picture at a time with a background service so that the user starts to see images faster than they currently are?

Thanks.

Answer 1

here is a rough example of how to do this:

public Void doInBackground(String... urls) {
    int len = urls.length;
    for(int i = 0; i < len; ++i) {
        Bitmap b = downloadImage(urls[i]);
        publishProgress(new Object[] {b, i});
    }
    return null;
}

public void onProgressUpdate(Object... values) {
    Bitmap b = (Bitmap)values[0];
    Integer bitmapIndex = (Integer)values[1];
    //replace the image at location "bitmapIndex" in your collection of images with "b"
    //update your adapter via notifyDataSetChanged
}

Use the AsyncTask‘s onProgressUpdate method to publish progress inside doInBackground. This method(onProgressUpdate) runs on the UI thread.