Flutter: some case scrollTo not working in ScrollablePositionedList-CodePudding

I'm working with an indexed list in flutter, I found this lib: ScrollablePositionedList, when I put the action scrollTo / jumpTo on button tap, it works but when I put it before the returning built, it throws error:

E/flutter ( 3018): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: 'package:scrollable_positioned_list/src/scrollable_positioned_list.dart': Failed assertion: line 236 pos 12: '_scrollableListState != null': is not true.

Here is my code:

import 'package:flutter/material.dart';

import 'package:scrollable_positioned_list/scrollable_positioned_list.dart';

class ReadScreen extends HookWidget {
  const ReadBibleScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    
    ItemScrollController idxCtrl = ItemScrollController();
 /**Here, the code throw the Error */
    bc.listenable.listen(
      (p0) {
          idxCtrl.scrollTo(index: p0, duration: Duration(seconds: 1));//-->Not Working
        }
    );

    return Container(
      decoration: BoxDecoration(gradient: kGradPink),
     ...
          child:
  /**Here, the code work */
          IconButton(
              onPressed: () {
                idxCtrl.jumpTo(index: 10); //------------------------->Working
              
              },
              icon: Icon(Icons.tab)),
          ...
           ScrollablePositionedList.builder(
            
              itemScrollController: idxCtrl,
              ...
              itemCount: ...
              itemBuilder: (BuildContext context, int index) {
                return Container(
                  ...

CodePudding user response：

The code is executed line by line from top to bottom. In your case, ItemScrollController is instantiated but not linked to ScrollablePositionedList. It means that it doesn't aware of Object to which it belongs yet.

To make it work you can add the lines inside itemBuilder

class ReadScreen extends HookWidget {
  const ReadBibleScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(gradient: kGradPink),
     ...
          child:
          IconButton(
              onPressed: () {
                idxCtrl.jumpTo(index: 10);
              },
              icon: Icon(Icons.tab)),
          ...
           ScrollablePositionedList.builder(
              itemScrollController: idxCtrl,
              ...
              itemCount: ...
              itemBuilder: (BuildContext context, int index) {
                ItemScrollController idxCtrl = ItemScrollController();
                bc.listenable.listen(
                  (p0) {
                    idxCtrl.scrollTo(index: p0, duration: Duration(seconds: 1));
                }
            );
                return Container(
                  ...

CodePudding user response：

Try wrapping your scrollTo call inside an addPostFrameCallback, this way the code will run after the build method has finished.

  @override
  Widget build(BuildContext context) {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      idxCtrl.scrollTo(index: p0, duration: Duration(seconds: 1));
    });
...

CodePudding user response：

I used the answer here, it did the job as well: Flutter: Error thrown in some case using ScrollablePositionedList

sorry, the post was duplicated