createAnimation method
Implementation
Animation<Alignment> createAnimation() {
assert(!_transitionCompleter.isCompleted,
'Cannot reuse a $runtimeType after disposing it.');
assert(_controller != null);
return AlignmentTween(begin: _initialAlignment, end: _endAlignment).animate(
CurvedAnimation(
parent: _controller!,
curve: toastMessageBar.forwardAnimationCurve,
reverseCurve: toastMessageBar.reverseAnimationCurve,
),
);
}