How to schedule heavy work for later display for Listviews?

Question

I have a listview with 200 items. I use a custom view for each row. There is a code that takes some time to calculate, and because of this the list hangs out on scrolling and loads in slow (2-3sec).

I have subclassed SimpleCursorAdapter, and using Filterable and SectionIndexer.

I have in mind to show initially the name of the record, and put in a thread the calculation, and will show up later when it's done.

How do I push back some work, and later update the listview to include the calculated data? This should show up on fly without user interaction.

Answer 1

Since android the Android UI is singlethreaded it will be blocked whenever you perform a long operation.

You could do regular java threading and have a Handler() in the main UI class that you can feed back information into. But..

The simplest way would be to create an AsyncTask(). They are java threads with a slight change. They can perform a UI operation before/after the main calculation. So for example:

 private class AndroidThread extends AsyncTask {
      protected Object doInBackground(Object... params) {
           return result;
      }

      protected void onPostExecute(Object result) {
           // do things here with the result of the doInBackground function
           // Like: "UiElement"."performTask(result)"
      }
 }

For more information on AsyncTask see this