indexOfFirstChild property Null safety

int indexOfFirstChild

The index of the first child of the viewport relative to the center child.

For example, the center child has index zero and the first child in the reverse growth direction has index -1.


int get indexOfFirstChild {
  assert(center != null);
  assert(center!.parent == this);
  assert(firstChild != null);
  int count = 0;
  RenderSliver? child = center;
  while (child != firstChild) {
    count -= 1;
    child = childBefore(child!);
  return count;