AnimatedPositioned - how to change position automatically without pressing button

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 :

have you put your postFrameCallback inside the `initState` method? — Pierre Monier, Jul 19 '22 at 10:15
yes i did. but even when the "selected = true" the widget doesnt change position — ILii, Jul 19 '22 at 10:20
can you explain more what is your need as exactly ? .. do you mean that you need your widget to be animated at the start of screen build ? if yes so what's the required duration ? — Mohammed Hamdan, Jul 19 '22 at 11:16

score 0 · Answer 1 · answered Jul 19 '22 at 10:48

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

AnimatedPositioned - how to change position automatically without pressing button

1 Answers1