addItem method
Implementation
bool addItem(
int index, RenderBox box, double topOffset, bool sizeChanged, T data) {
final existed = _sizeMap.containsKey(index);
final size = box.size;
_sizeMap[index] = size;
_offsetMap[index] = topOffset;
_notifyListeners(
index: index,
size: size,
topOffset: topOffset,
isFirst: !existed,
sizeChanged: sizeChanged,
data: data,
);
return !existed;
}