feat: support custom AutoScrollController for Scrollbar compatibility

[MTsung]

遇到問題

想使用 Scrollbar 或 RawScrollbar 顯示捲軸時出現錯誤訊息

════════ Exception caught by scheduler library ═════════════════════════════════
The following assertion was thrown during a scheduler callback:
The Scrollbar's ScrollController has no ScrollPosition attached.
A Scrollbar cannot be painted without a ScrollPosition.
The Scrollbar attempted to use the provided ScrollController. This ScrollController should be associated with the ScrollView that the Scrollbar is being applied to.
When providing your own ScrollController, ensure both the Scrollbar and the Scrollable widget use the same one.

修改方式

參考 Stack Overflow 69853729，允許從外部傳入 AutoScrollController。

修改後使用範例

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

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

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

class TestPageState extends State<TestPage> {
  final AutoScrollController controller = AutoScrollController();

  String md() {
    return '''test
''';
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('test')),
      body: Container(
        color: Colors.white,
        padding: EdgeInsets.all(10),
        height: 250,
        child: RawScrollbar(
          controller: controller,
          thumbVisibility: true,
          child: MarkdownWidget(
            autoScrollController: controller,
            padding: EdgeInsets.all(12),
            shrinkWrap: true,
            data: md() * 100,
          ),
        ),
      ),
    );
  }
}

截圖

[RoBoT095]

Maybe add null check to _controller.dispose() as the user will probably be disposing controller

@override
void dispose() {
  clearState();
  if (widget.controller == null) _controller.dispose();
  _tocController?.jumpToIndexCallback = null;
  super.dispose();
}

As well as a way to remove controller from ListView.builder without not making controller null

controller: widget.autoScrollController != null &&
        widget.physics != NeverScrollableScrollPhysics()
    ? null
    : _controller,

This is what I did to make scroll position syncing between edit and preview mode, but also be able to use table of contents jump to index

[rebaz94]

controller: widget.autoScrollController != null &&
widget.physics != NeverScrollableScrollPhysics()
? null
: _controller

@RoBoT095

I have same problem of syncing position, just providing the controller fix the issue and be sure not disposing if controller provided.

[MTsung]

Thanks @RoBoT095 and @rebaz94 for raising this 🙏
I’ve updated the code so that the controller is now safely disposed

-    _controller.dispose();
+    if (widget.autoScrollController == null) _controller.dispose();