CODEWITHSUNDEEP
androidflutterdart
Nimish Bansal
Nimish Bansal

Reputation: 1759

Flutter SizeTransition not working correctly.Size transition behaving like I am sliding widget

I was trying to learn Flutter SizeTransition. I used SizeTransition and provided sizeFactor as animation and provided tween from 0 to 1. I made a function execute in build that gets exectued after some seconds, What I expected was that the size of logo will increase and decrease when animation is forward and reverse respectively. But what I noticed that logo first moves down and then goes back up.(like a Slide Transition)

widget to test for SizeTransition

import 'dart:async';

import 'package:flutter/material.dart';


class LogoApp extends StatefulWidget {
  _LogoAppState createState() => _LogoAppState();
}

class _LogoAppState extends State<LogoApp> with TickerProviderStateMixin {
  AnimationController _animationController;
  Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _animationController =
        AnimationController(vsync: this, duration: Duration(seconds: 4));
    _animation = _animationController.drive(Tween(begin: 0, end: 1));
  }

  int ctr = 0;
  @override
  Widget build(BuildContext context) {
    ctr += 1;
    print("build$ctr");
    execute(); //function that executes forward()/reverse() methods of animationController
    return SizeTransition(
      sizeFactor: _animation,
      child: Center(
        child: FlutterLogo(),
      ),
    );
  }

  void execute() async {
    Future.delayed(const Duration(seconds: 2), () {
      _animationController.forward();
    });
    Future.delayed(const Duration(seconds: 4), () {
      _animationController.reverse();
    });
  }
}

main.dart

void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: LogoApp(),
    );
  }
}

I have tried a lot but no success. What else can I do?

Upvotes: 1

Views: 1675

Answers (1)

SilSur
SilSur

Reputation: 509

I think what you actually meant to implement was a ScaleTransition() instead of a SizeTransition().

It's a pretty straightforward fix:

int ctr = 0;
@override
Widget build(BuildContext context) {
  ctr += 1;
  print("build$ctr");
  execute(); //function that executes forward()/reverse() methods of animationController
  return Center(
    child: ScaleTransition(
      scale: _animation,
      child: FlutterLogo(),
    ),
  );
}

You also need to move the Center() widget one level up (as shown in the code) to ensure that the entire animation is anchored to the center of the display - as you originally intended it to be.

Upvotes: 2

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