Why is ListView.getCheckedItemPositions() not returning correct values?

The app has a ListView with multiple-selection enabled, in the UI it works as expected. But when I read the values out using this code:

Log.i(TAG,"Entered SearchActivity.saveCategoryChoice()");
SparseBooleanArray checkedPositions = categorySelector.getCheckedItemPositions();
Log.i(TAG,"checkedPositions: " + checkedPositions.size());

if (checkedPositions != null) {
  int count = categoriesAdapter.getCount();
  for ( int i=0;i<count;i++) {
    Log.i(TAG,"Selected items: " + checkedPositions.get(i));
  }
}

I get this output, no matter what state each checkbox is in:

Entered SearchActivity.saveCategoryChoice()
checkedPositions: 0
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false
Selected items: false

The SparseBooleanArray seems to return false for any non-existent item, so the source of the problems seems to be that getCheckedItemPositions() is returning an empty array. The method is behaving as if there are no items in the ListView, but there are.

I can see from the docs that no values are returned when the ListView is not set up as multi-select, but it is, using this statement:

categorySelector.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);

In my scenario, the adapter I'm using is a subclass of ArrayAdapter, and (without any solid evidence) I suspect this may be the cause, though I can't see why it shouldn't work.

kcoppock is right, you need to use valueAt(), the working code should be

SparseBooleanArray checkedItems = categorySelector.getCheckedItemPositions();
if (checkedItems != null) {
    for (int i=0; i<checkedItems.size(); i++) {
        if (checkedItems.valueAt(i)) {
            String item = categorySelector.getAdapter().getItem(
                                  checkedItems.keyAt(i)).toString();
            Log.i(TAG,item + " was selected");
        }
    }
}

I remember having an issue with this myself a while back. Here is my previous question, which isn't directly related to your issue, but contains some code that may help. What you might want to try is using checkedPositions.valueAt(int index) rather than checkedPositions.get(int index). I think that may be what you're actually looking for.