create method
Marks the resource created.
Not @mustBeOverridden: this implementation is complete and usable on
its own, and requiring every subclass to override it only produced empty
overrides. Subclasses that do override must still call super.
Implementation
@override
@mustCallSuper
FutureOr<void> create() {
if (_disposed) {
throw StateError('Resource has been disposed');
}
if (_created) {
throw StateError('Resource has already been created');
}
_created = true;
}