canFetchPrev property
Determines whether more data can be fetched when scrolling backward.
If this method returns false, it is determined that data fetching has ended, fetchPrev is not executed, and no further data will be fetched.
index is the last index of the data to be fetched next.
For example, if data 20-39 is currently displayed, the previous data will be fetched starting from 19.
Implementation
final bool Function(int index)? canFetchPrev;