onRefresh property Null safety

RefreshCallback? onRefresh
final

Callback invoked when pulled by refreshTriggerPullDistance.

If provided, must return a Future which will keep the indicator in the RefreshIndicatorMode.refresh state until the Future completes.

Can be null, in which case a single frame of RefreshIndicatorMode.armed state will be drawn before going immediately to the RefreshIndicatorMode.done where the sliver will start retracting.

Implementation

final RefreshCallback? onRefresh;