动画可滚动小部件以在另一个小部件滚动时填充彼此的空间

Question

这是一个包含三个主要小部件的应用程序：大小框和两个可滚动的ListViews，一个在SizedBox() 内，另一个在Expanded() 内。

我要做的是让BottomList在滚动时向上移动并占据TopList的位置，如果TopList滚动则移动到BottomList的原始位置。我如何实现这一目标？

MRE：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('two scrolls')),
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          // Widget1: this box should stay in place
          SizedBox(
            height: MediaQuery.of(context).size.height / 5,
            child: Container(
              color: Colors.purple,
            ),
          ),
          // TopList: this box should shrink to the top until it hits some minimum height, on scroll in BottomList
          // If it is scrolled after Widget3 took all the space, expand its contents to bottom to a set height.
          SizedBox(
            // has half of remaining height
            height: MediaQuery.of(context).size.height / 2 - MediaQuery.of(context).size.height / 5 - kToolbarHeight,
            child: ListView(
              children: [
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
              ],
            ),
          ),
          const Divider(height: 16, thickness: 0.5, color: Colors.black),
          // BottomList: on scroll, should expand upwards to fill the space of TopList until it hits TopList_minHeight, then scroll as usual.
          // On scroll of TopList, should move to it's original position.
          Expanded(
            child: ListView(
              children: [
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
              ],
            ),
          )
        ],
      ),
    );
  }
}

Answer 1

您可以将侦听器添加到调整顶部列表小部件高度的ScrollController。 请注意，在这种情况下，您需要手动处理 ScrollController。

import 'package:flutter/material.dart';
import 'dart:math';

void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

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

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late final ScrollController topScrollController;
  late final ScrollController bottomScrollController;
  double topOffset = 0;
  @override
  void initState() {
    super.initState();
    topScrollController = ScrollController();
    topScrollController.addListener(() {
      setState(() {
        topOffset = 0;
      });
    });

    bottomScrollController = ScrollController();
    bottomScrollController.addListener(() {
      setState(() {
        topOffset = bottomScrollController.offset;
      });
    });
  }

  @override
  void dispose() {
    topScrollController.dispose();
    bottomScrollController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final topMaxHeight = MediaQuery.of(context).size.height / 2 -
        MediaQuery.of(context).size.height / 5 -
        kToolbarHeight;
    const topMinHeight = 50.0;
    double height = topOffset <= 200
        ? topMaxHeight
        : max(topMaxHeight + 200 - topOffset, topMinHeight);

    return Scaffold(
      // appBar: AppBar(title: const Text('two scrolls')),
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          // Widget1: this box should stay in place
          SizedBox(
            height: MediaQuery.of(context).size.height / 5,
            child: Container(
              color: Colors.purple,
            ),
          ),
          // TopList: this box should shrink to the top until it hits some minimum height, on scroll in BottomList
          // If it is scrolled after Widget3 took all the space, expand its contents to bottom to a set height.

          SizedBox(
            // has half of remaining height
            height: height,
            child: ListView(
              controller: topScrollController,
              children: [
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.green,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.purple,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.green,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.purple,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.green,
                ),
              ],
            ),
          ),
          const Divider(height: 16, thickness: 0.5, color: Colors.black),
          // BottomList: on scroll, should expand upwards to fill the space of TopList until it hits TopList_minHeight, then scroll as usual.
          // On scroll of TopList, should move to it's original position.
          Expanded(
            child: ListView(
              controller: bottomScrollController,
              children: [
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.blue,
                ),
                Container(
                  width: 160.0,
                  height: 160.0,
                  color: Colors.red,
                ),
              ],
            ),
          )
        ],
      ),
    );
  }
}