createTween method
Returns a Tween that the AnimationImpl
can use to interpolate between
value and animatedValue.
The returned Tween must always evaluate to T
even though the signature
allows for a nullable type. The signature is chosen to allow the usage of
Tweens that only return null
when neither Tween.begin nor
Tween.end are set, which AnimationImpl
will never do.
Implementation
@override
Tween<Size?> createTween() => SizeTween();