Ever wanted to scroll down to a widget in a scroll view? Now you can, Anchor Scroll to the rescue! - by Simon Lightfoot - 15/11/2019

anchor_scroll.dart

// MIT License
//
// Copyright (c) 2019 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:flutter/material.dart';

/// Example: context.anchorScroll(Key('test'));
extension AnchorScrollContext on BuildContext {
  Future<void> anchorScroll(
    Key anchorKey, {
    duration = const Duration(milliseconds: 350),
    curve = Curves.easeOutExpo,
  }) =>
      scrollToAnchor(this, anchorKey, duration: duration, curve: curve);
}

Future<void> scrollToAnchor(
  BuildContext context,
  Key anchorKey, {
  duration = const Duration(milliseconds: 350),
  curve = Curves.easeOutExpo,
}) {
  Element? found;

  void visitElement(Element el) {
    if (el.widget.key == anchorKey) {
      found = el;
      return;
    }
    el.visitChildren(visitElement);
  }

  context.visitChildElements(visitElement);
  if (found == null) {
    throw StateError('No widget with key found');
  }

  final scrollable = Scrollable.of(context);
  if (scrollable == null) {
    throw StateError('Widget not in scrollable context');
  }

  final scrollableBox = scrollable.context.findRenderObject();
  final anchorBox = found!.findRenderObject() as RenderBox?;
  if (anchorBox == null || scrollableBox == null) {
    throw StateError('Widget not laid out. Try SingleChildScrollView.');
  }

  final anchorOffset = anchorBox.localToGlobal(
    Offset.zero,
    ancestor: scrollableBox,
  );
  return scrollable.position.animateTo(
    scrollable.position.pixels + anchorOffset.dy,
    duration: duration,
    curve: curve,
  );
}

Hi Simon, i tried this:

body:ListView(
    children: List.generate(500, (index) {
      return ListTile(
        key: Key("$index"),
        title: Text(
          "Index $index",
        ),
      );
    }).toList(),
  ),
floatingActionButton: FloatingActionButton(
    child: Text("~"),
    onPressed: () {
      context.anchorScroll(Key("499"));
    },
),

but i got Bad state: No widget with key found
Could you helping me by providing a simple example ?

@SergioEric use a SingleChildScrollView

body: SingleChildScrollView(
        child: Column(
          children: List.generate(500, (index) {
            return ListTile(
              key: Key("$index"),
              title: Text(
                "Index $index",
              ),
            );
          }).toList(),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: (){
          context.anchorScroll(Key(Random().nextInt(499).toString()));
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),

context.anchorScroll(Key(Random().nextInt(499).toString()));

Same thing goes for listview.builder can you please share example...??