createRecognizer method
The gesture that starts a drag from this handle.
Override in a subclass to change it, the way
TreeDelayedDragHandle does. A named constructor cannot vary
behaviour without a discriminating field, so subclassing is the
mechanism, matching ReorderableDelayedDragStartListener.
Must return a MultiDragGestureRecognizer: the row services exactly one protocol, and mixing in a single-pointer recognizer would mean two incompatible callback shapes.
Implementation
@protected
MultiDragGestureRecognizer createRecognizer() {
return ImmediateMultiDragGestureRecognizer(debugOwner: this);
}