AnimatedPositioned - how to change position automatically without pressing button - flutter

Question

i want to use the animated positioned class to change widget position with the launch of the screen without pressing a button!
class MyStatefulWidget extends StatefulWidget {
const MyStatefulWidget({Key? key}) : super(key: key);
#override
State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
bool selected = false;
#override
Widget build(BuildContext context) {
return SizedBox(
width: 200,
height: 350,
child: Stack(
children: <Widget>[
AnimatedPositioned(
width: selected ? 200.0 : 50.0,
height: selected ? 50.0 : 200.0,
top: selected ? 50.0 : 150.0,
duration: const Duration(seconds: 2),
curve: Curves.fastOutSlowIn,
child: GestureDetector(
onTap: () {
setState(() {
selected = !selected;
});
},
child: Container(
color: Colors.blue,
child: const Center(child: Text('Tap me')),
),
),
),
],
),
);
}
}
i tried to change it by using a WidgetsBinding like this :
WidgetsBinding.instance.addPostFrameCallback((_) {
setState(() {
selected = true;
});
print(' widget binding : $selected');
});
it works fine but the problem was that it doesnt excuted once, it keeps running and change the value to true! like this :

Answer 1

I copy/past the code you have shared to see what's going on, and it's working just fine for me. I have this code
import 'package:flutter/material.dart';
void main() async {
return runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return const MaterialApp(
home: Scaffold(
body: MyStatefulWidget(),
),
);
}
}
class MyStatefulWidget extends StatefulWidget {
const MyStatefulWidget({Key? key}) : super(key: key);
#override
State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_) {
setState(() {
selected = true;
});
print(' widget binding : $selected');
});
}
bool selected = false;
#override
Widget build(BuildContext context) {
return SizedBox(
width: 200,
height: 350,
child: Stack(
children: <Widget>[
AnimatedPositioned(
width: selected ? 200.0 : 50.0,
height: selected ? 50.0 : 200.0,
top: selected ? 50.0 : 150.0,
duration: const Duration(seconds: 2),
curve: Curves.fastOutSlowIn,
child: GestureDetector(
onTap: () {
setState(() {
selected = !selected;
});
},
child: Container(
color: Colors.blue,
child: const Center(child: Text('Tap me')),
),
),
),
],
),
);
}
}
The animation is run only once, when the postFrameCallback is called. The problem must be elsewhere