debugFillDescription method Null safety
override
Add additional information to the given description for use by toString.
This method makes it easier for subclasses to coordinate to provide a high-quality toString implementation. The toString implementation on the State base class calls debugFillDescription to collect useful information from subclasses to incorporate into its return value.
Implementations of this method should start with a call to the inherited
method, as in super.debugFillDescription(description).
Implementation
@override
void debugFillDescription(List<String> description) {
super.debugFillDescription(description);
description.add('${context.runtimeType}');
description.add('$physics');
description.add('$activity');
description.add('$userScrollDirection');
}