import 'package:flutter/material.dart';

class PositionedTransitionWidget extends StatefulWidget {
@override
_PositionedTransitionWidgetState createState() =>
_PositionedTransitionWidgetState();
}

class _PositionedTransitionWidgetState extends State<PositionedTransitionWidget>
with SingleTickerProviderStateMixin {
final RelativeRectTween relativeRectTween = RelativeRectTween(
begin: RelativeRect.fromLTRB(100, 100, 0, 0),
end: RelativeRect.fromLTRB(0, 0, 50, 50),
);
AnimationController controller;
bool status = true;

@override
void initState() {
controller = AnimationController(
vsync: this,
duration: const Duration(seconds: 1),
);
super.initState();
}

@override
Widget build(BuildContext context) {
return Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Container(
color: Colors.pink,
width: 300,
height: 300,
child: Stack(
children: <Widget>[
PositionedTransition(
rect: relativeRectTween.animate(controller),
child: Container(
color: Colors.orange,
width: 200,
height: 200,
padding: EdgeInsets.all(20),
child: FlutterLogo(),
),
),
],
),
),
RaisedButton(
onPressed: () {
status ? controller.forward() : controller.reverse();
status = !status;
},
child: Text("Change Positione"),
)
],
);
}
}