Question

I have a ListActivity that launches a task to hit a web service and display the results in a ListView. Each one of the results has an image ID attached to it.

I wrote a method that will get the image IDs of the rows displayed on screen (firstVisiblePosition() to lastVisiblePosition()) and launch a task to query another web service to get the images to display for those items. I call this method when the list’s scroll state becomes SCROLL_STATE_IDLE. This makes it so the user can scroll and the task to get the images for the visible rows does not execute until the scrolling stops, preventing it from looking up images for off-screen rows.

My issue is that when the results initially show in the ListView, I can’t find a good way to call my method to look up which image IDs to query for. Apparently, calling this method right after calling setAdapter does not work (I’m guessing because some of the ListView’s work happens asynchronously). I am using multiple Adapter’s (for reasons not pertinent to this post), so I need a good way of waiting for the list items to show before I call my method to get the IDs.

Any ideas?

Answer 1

After you’ve set the adapter or called notifyDatasetChanged() on the adapter, add your “load images” code to the list’s post queue as a Runnable:

list.post( new Runnable() {
    @Override
    public void run() {
    //do stuff
    }
  });