AnimatedSize不发推特，除非有父小部件

Question

我观察到，除非AnimatedSize小部件有父Container，否则不会有推特。在下面的代码中，如果你点击正方形，方块就会变成零大小。如果我删除AnimatedSize小部件的父部件，小部件就会立即变为零大小，而不需要发推文。此外，如果我保留父Container，但删除color字段或使其透明，则不会发布推文。

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({super.key});

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  double _size = 200.0;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () => setState(() {
        _size = 0;
      }),
      child: Container( // No tweening if this widget is removed
        color: Colors.red, // No tweening if this field is removed or made transparent
        child: AnimatedSize(
            curve: Curves.easeIn,
            duration: const Duration(seconds: 1),
            child: Container(
              width: _size,
              height: _size,
              color: Colors.red,
            )),
      ),
    );
  }
}

为什么需要父部件？理想情况下，我希望在没有家长需要的情况下，推特会发生。

Answer 1

对于TweenAnimationBuilder，我不需要外部小部件：：

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({super.key});

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  double _endSize = 200.0;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () => setState(() {
        _endSize = 0;
      }),
      child: TweenAnimationBuilder<double>(
          tween: Tween<double>(begin: 200.0, end: _endSize),
          curve: Curves.easeIn,
          duration: const Duration(seconds: 1),
          builder: (context, size, child) {
            return Container(
              width: size,
              height: size,
              color: Colors.red,
            );
          }),
    );
  }
}