Number of visible items bug with defersItemViewLoading

[edkimmel]

if (_defersItemViewLoading)
{
    startIndex = _currentItemIndex - ceilf(x / itemWidth) - 1;
    numberOfVisibleItems = ceilf(width / itemWidth) + 3;
}

//create indices
numberOfVisibleItems = MIN(numberOfVisibleItems, _numberOfItems);

Is the culprit code. Here's the use case.

• I have a list of 2 items
• I show 2 (or more) items per page.
• I do not have wrapping enabled.
• I do have defersItemViewLoading enabled.

// startIndex is 0
// numberOfVisibleItems is 2
if (_defersItemViewLoading)
{
    startIndex = _currentItemIndex - ceilf(x / itemWidth) - 1;
    // startIndex = -2
    numberOfVisibleItems = ceilf(width / itemWidth) + 3; 
   // numberOfVisibleItems is 3+, more than my count
}

//create indices
numberOfVisibleItems = MIN(numberOfVisibleItems, _numberOfItems);
// numberOfVisibleItems is set back to 2.
// startIndex is still -2.

In the code following this block, it will clamp the indexes to 0, and only load view 0, leaving a space where view 1 should have been.

A possible solution I've found is to modify the code to respect wrapping in this block.

        if (_defersItemViewLoading)
        {
            NSInteger newStartIndex = _currentItemIndex - ceilf(x / itemWidth) - 1;
            if (!_wrapEnabled) newStartIndex = MAX(newStartIndex, 0);
            numberOfVisibleItems += abs(newStartIndex - startIndex) + 2;
            if (!_wrapEnabled && newStartIndex + numberOfVisibleItems > _numberOfItems) {
                numberOfVisibleItems = _numberOfItems - newStartIndex;
            }
            startIndex = newStartIndex;
        }
        else
        {
           numberOfVisibleItems = MIN(numberOfVisibleItems, _numberOfItems);
        }

I'm sure this logic could be cleaner than a bunch of if statements.