estimateMaxScrollOffset method

double estimateMaxScrollOffset (SliverConstraints constraints, { int firstIndex, int lastIndex, double leadingScrollOffset, double trailingScrollOffset })

Called to estimate the total scrollable extents of this object.

Must return the total distance from the start of the child with the earliest possible index to the end of the child with the last possible index.

Implementation 

double estimateMaxScrollOffset(SliverConstraints constraints, {
  int firstIndex,
  int lastIndex,
  double leadingScrollOffset,
  double trailingScrollOffset,
});