childCount property
Called to obtain a precise measure of the total number of children.
Must return the number that is one greater than the greatest index
for
which createChild
will actually create a child.
This is used when createChild cannot add a child for a positive index
,
to determine the precise dimensions of the sliver. It must return an
accurate and precise non-null value. It will not be called if
createChild is always able to create a child (e.g. for an infinite
list).
Implementation
int get childCount;