How to get full size of a ScrollController

Question

I've attached a ScrollController to a CustomScrollView of [SliverAppBar, SliverList]

In a default case I would use reverse:true and animateTo (0.0) to move the scroll to the last element added but in this case using reverse would also reverse the SliverAppBar/SliverList order !

So I'd like to use animateTo ( sizeOfScrollableAfterElementAdded ) but I can't find this value.

Thank you !

Answer 1

You can use _scrollController.position.maxScrollExtent to scroll to the end. Make sure to do this in a post-frame callback so that it will include the new item you just added.

Here is an example of a sliver list that scrolls to the end as more items are added.

import 'package:flutter/scheduler.dart'; import 'package:flutter/material.dart';  void main() {   runApp(new MyApp()); }  class MyApp extends StatelessWidget {   @override   Widget build(BuildContext context) {     return new MaterialApp(       title: 'Flutter Demo',       home: new MyHomePage(),     );   } }  class MyHomePage extends StatefulWidget {   State createState() => new MyHomePageState(); }   class MyHomePageState extends State<MyHomePage> {   ScrollController _scrollController = new ScrollController();    List<Widget> _items = new List.generate(40, (index) {     return new Text("item $index");   });    @override   Widget build(BuildContext context) {     return new Scaffold(       floatingActionButton: new FloatingActionButton(         child: new Icon(Icons.arrow_downward),         onPressed: () {           setState(() {             _items.add(new Text("item ${_items.length}"));           });           SchedulerBinding.instance.addPostFrameCallback((_) {             _scrollController.animateTo(               _scrollController.position.maxScrollExtent,               duration: const Duration(milliseconds: 300),               curve: Curves.easeOut,             );           });         },       ),       body: new CustomScrollView(         controller: _scrollController,         slivers: [           new SliverAppBar(             title: new Text('Sliver App Bar'),           ),           new SliverList(             delegate: new SliverChildBuilderDelegate(               (context, index) => _items[index],               childCount: _items.length,             ),           ),         ],       ),     );   } }