@Override
    public int getItemCount() {
        if (sections == null) {
            buildSectionIndex();
        }
        return totalNumberOfItems;
    }
Post an action to be run later.
RecyclerView doesn't like being mutated during a scroll. We can't detect when a
scroll is actually happening, unfortunately, so the best we can do is post actions
from notify* methods to be run at a later date.

@param action action to run
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/section/SectioningAdapter.java