Trigger animations on widget load flutter - flutter

Question

So, I have a AnimatedPositioned widget in my widget tree, which contains a form. I want the AnimatedPositioned widget to slide up from bottom when user navigates to the screen. Now, there are many tutorials which show how to do this when user clicks a button using the setState method. But how do I trigger this automatically when this screen is loaded?

Answer 1

The "right" way to do that would be not to use an implicit animation widget like AnimatedPositioned and instead use an explicit animation. Where you start your AnimationController in the initState of a StatefulWidget.
But just technically you could set the "destination" values for your AnimatedPositioned widget in a Future so that the value changes on the next frame. You try remoing the Future to see that otherwise the widget renders at its end position.
This way is not recommended but possible:
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key}) : super(key: key);
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
double _dist = 0.0;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(children: [
AnimatedPositioned(
child: Text('Hello Words'),
duration: Duration(seconds: 5),
left: _dist,
top: _dist,
),
]),
);
}
#override
initState() {
super.initState();
Future(() {
setState(() {
_dist = 250.0;
});
});
}
}