buildAnimatedChild method
Returns the transformed widget for the current animation tick. The
child argument is the unchanged widget.child, ready to be wrapped
in Transform, Opacity, etc.
Implementation
@override
Widget buildAnimatedChild(BuildContext context, Widget child) {
return Transform.translate(
offset: Offset(0, _translate.value),
child: Opacity(opacity: _opacity.value, child: child),
);
}