android - Flutter SizeTransition 无法正常工作。Size transition 的行为就像我在滑动小部件一样

Question

我正在尝试学习 Flutter SizeTransition。我使用 SizeTransition 并提供 sizeFactor 作为动画并提供从 0 到 1 的补间。我在构建中执行了一个函数，该函数在几秒钟后执行，我期望的是当动画分别向前和向后时 Logo 的大小会增加和减小.但是我注意到 Logo 先向下移动然后又向上移动。(就像幻灯片过渡一样)

用于测试 SizeTransition 的小部件

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();
    });
  }
}

主.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(),
    );
  }
}

我尝试了很多，但都没有成功。我还能做什么？

Answer 1

我认为您实际想要实现的是 ScaleTransition() 而不是 SizeTransition()。

这是一个非常简单的修复:

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(),
    ),
  );
}

您还需要将 Center() 小部件向上移动一层(如代码中所示)以确保整个动画锚定在显示的中心 - 正如您最初预期的那样成为。