flutter - How to auto scroll to index with dynamic height programmatically

Question

According to Flutter's issue here , The Auto-Scroll to Index where each cell/item has dynamic height is currently not supported. I have tried another solution but no works.

so, What's a temporary solution to make ListView with AutoScroll for dynamic height?

Any Idea?

Solution 1

Your question

so, What's a temporary solution to make ListView with AutoScroll for dynamic height?

Screen Record

solution

scroll-to-index package

This package provides the scroll to index mechanism for fixed/variable row height for Flutter scrollable widget.

This is a widget level library, means you can use this mechanism inside any Flutter scrollable widget.

Usage

pubspec.yaml

 scroll_to_index: any

Example From quire-io/scroll-to-index: scroll to index with fixed/variable row height inside Flutter scrollable widget

Usage - Controller

controller.scrollToIndex(index, preferPosition: AutoScrollPosition.begin)

Usage - ListView

ListView(
scrollDirection: scrollDirection,
controller: controller,
children: randomList.map<Widget>((data) {
    final index = data[0];
    final height = data[1];
    return AutoScrollTag(
    key: ValueKey(index),
    controller: controller,
    index: index,
    child: Text('index: $index, height: $height'),
    highlightColor: Colors.black.withOpacity(0.1),
    );
}).toList(),
)

Extra anunixercoder asked

Is this for finite or infinite list ?

Using ListView.builder to simulate an infinite list

    ListView.builder(
    scrollDirection: scrollDirection,
    controller: controller,
    itemBuilder: (context, i) => Padding(
      padding: EdgeInsets.all(8),
      child: _getRow(i, (min + rnd.nextInt(max - min)).toDouble()),
    ),

It got 18 right of 22 tries , about (81%) or near to it

Screen Record

so it not suported 100%

Ref :

• scroll_to_index | Flutter Package

• https://raw.githubusercontent.com/quire-io/scroll-to-index/master/example/lib/main.dart

• How to get a random number from range in dart? - Stack Overflow

1st screen record code

//Copyright (C) 2019 Potix Corporation. All Rights Reserved.
//History: Tue Apr 24 09:29 CST 2019
// Author: Jerry Chen

import 'dart:math' as math;

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Scroll To Index Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Scroll To Index Demo'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  static const maxCount = 100;
  final random = math.Random();
  final scrollDirection = Axis.vertical;

  AutoScrollController controller;
  List<List<int>> randomList;

  @override
  void initState() {
    super.initState();
    controller = AutoScrollController(
      viewportBoundaryGetter: () => Rect.fromLTRB(0, 0, 0, MediaQuery.of(context).padding.bottom),
      axis: scrollDirection
    );
    randomList = List.generate(maxCount, (index) => <int>[index, (1000 * random.nextDouble()).toInt()]);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ListView(
        scrollDirection: scrollDirection,
        controller: controller,
        children: randomList.map<Widget>((data) {
          return Padding(
            padding: EdgeInsets.all(8),
            child: _getRow(data[0], math.max(data[1].toDouble(), 50.0)),
          );
        }).toList(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _scrollToIndex,
        tooltip: 'Increment',
        child: Text(counter.toString()),
      ),
    );
  }

  int counter = -1;
  Future _scrollToIndex() async {
    setState(() {
      counter++;

      if (counter >= maxCount)
        counter = 0;
    });

    await controller.scrollToIndex(counter, preferPosition: AutoScrollPosition.begin);
    controller.highlight(counter);
  }

  Widget _getRow(int index, double height) {
    return _wrapScrollTag(
      index: index,
      child: Container(
        padding: EdgeInsets.all(8),
        alignment: Alignment.topCenter,
        height: height,
        decoration: BoxDecoration(
          border: Border.all(
            color: Colors.lightBlue,
            width: 4
          ),
          borderRadius: BorderRadius.circular(12)
        ),
        child: Text('index: $index, height: $height'),
      )
    );
  }

  Widget _wrapScrollTag({int index, Widget child})
  => AutoScrollTag(
    key: ValueKey(index),
    controller: controller,
    index: index,
    child: child,
    highlightColor: Colors.black.withOpacity(0.1),
  );
}

2nd screen record code :

//Copyright (C) 2019 Potix Corporation. All Rights Reserved.
//History: Tue Apr 24 09:29 CST 2019
// Author: Jerry Chen

import 'dart:math' as math;

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Scroll To Index Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Scroll To Index Demo'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final scrollDirection = Axis.vertical;
  var rnd = math.Random();
  int min = 50;
  int max = 200;
  AutoScrollController controller;
  @override
  void initState() {
    super.initState();
    controller = AutoScrollController(
        viewportBoundaryGetter: () =>
            Rect.fromLTRB(0, 0, 0, MediaQuery.of(context).padding.bottom),
        axis: scrollDirection);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ListView.builder(
        scrollDirection: scrollDirection,
        controller: controller,
        itemBuilder: (context, i) => Padding(
          padding: EdgeInsets.all(8),
          child: _getRow(i, (min + rnd.nextInt(max - min)).toDouble()),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _scrollToIndex,
        tooltip: 'Increment',
        child: Text(counter.toString()),
      ),
    );
  }

  int counter = -1;
  Future _scrollToIndex() async {
    setState(() {
      counter++;
    });

    await controller.scrollToIndex(counter,
        preferPosition: AutoScrollPosition.begin);
    controller.highlight(counter);
  }

  Widget _getRow(int index, double height) {
    return _wrapScrollTag(
        index: index,
        child: Container(
          padding: EdgeInsets.all(8),
          alignment: Alignment.topCenter,
          height: height,
          decoration: BoxDecoration(
              border: Border.all(color: Colors.lightBlue, width: 4),
              borderRadius: BorderRadius.circular(12)),
          child: Text('index: $index, height: $height'),
        ));
  }

  Widget _wrapScrollTag({int index, Widget child}) => AutoScrollTag(
        key: ValueKey(index),
        controller: controller,
        index: index,
        child: child,
        highlightColor: Colors.black.withOpacity(0.1),
      );
}

Solution 2

This package might be the one you are looking for. You can assign id for each widget and enable an animation just like tags in HTML.

https://pub.dev/packages/scroll_to_id

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

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  final ScrollToId scrollToId = ScrollToId();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Scroll to ID',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Scroll to ID'),
        ),
        body: Stack(
          alignment: Alignment.topRight,
          children: [
            InteractiveScrollViewer(
              scrollToId: scrollToId,
              children: [
                ScrollContent(
                  id: '1',
                  child: Container(
                    height: 600,
                    color: Colors.green,
                  ),
                ),
                ScrollContent(
                  id: '2',
                  child: Container(
                    height: 800,
                    color: Colors.red,
                  ),
                ),
                ScrollContent(
                  id: '3',
                  child: Container(
                    height: 300,
                    color: Colors.yellow,
                  ),
                ),
                ScrollContent(
                  id: '4',
                  child: Container(
                    height: 700,
                    color: Colors.blue,
                  ),
                ),
              ],
            ),
            Container(
              decoration: BoxDecoration(
                border: Border.all(color: Colors.white, width: 3),
              ),
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: [
                  GestureDetector(
                    child: Container(
                      width: 100,
                      alignment: Alignment.center,
                      height: 50,
                      child: Text('1', style: TextStyle(color: Colors.white),),
                      color: Colors.green,
                    ),
                    onTap: () {
                      scrollToId.scroll(id: '1');
                    },
                  ),
                  GestureDetector(
                    child: Container(
                      width: 100,
                      alignment: Alignment.center,
                      height: 50,
                      child: Text('2', style: TextStyle(color: Colors.white),),
                      color: Colors.red,
                    ),
                    onTap: () {
                      scrollToId.scroll(id: '2');
                    },
                  ),
                  GestureDetector(
                    child: Container(
                      width: 100,
                      alignment: Alignment.center,
                      height: 50,
                      child: Text('3', style: TextStyle(color: Colors.white),),
                      color: Colors.yellow,
                    ),
                    onTap: () {
                      scrollToId.scroll(id: '3');
                    },
                  ),
                  GestureDetector(
                    child: Container(
                      width: 100,
                      alignment: Alignment.center,
                      height: 50,
                      child: Text('4', style: TextStyle(color: Colors.white),),
                      color: Colors.blue,
                    ),
                    onTap: () {
                      scrollToId.scroll(id: '4');
                    },
                  ),
                ],
              ),
            )
          ],
        ),
      ),
    );
  }
}

Comments

[questionasker]

Is this for finite or infinite list ?

[Mohamed Elrashid]

@anunixercoder , finite but no infinite , check the Answer for more details

[questionasker]

Hi, Can i use ListView.builder for finite list ?

[Zenko]

This solves for a list with irregular height but it does not solve for a list with real dynamic height (a.k.a height changes over time). I have a bloc that handles each row's data. When it fetches the data then the row will expand accordingly. Now I have no idea how to scroll to a certain index accurately. It is always off.