ScrollablePositionedList: calling the builder for an element that has been removed from the array

[arteminthesky]

ScrollablePositionedList: calling the builder for an element that has been removed from the array

[arteminthesky]

I seem to have found a similar problem, but one is closed by the author and it is not entirely clear how he solved it.
#42

I would be very happy if you could help me find a way to change the number of elements in the list so that this would not cause problems. (I suppose if the new list has more elements than it was, this should not cause a problem)

[AurelianTimu]

Having the same issue.

[vabawen]

+1

Code Sample

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State<MyHomePage> {
  List<String> titles = [];
  ItemScrollController scrollController = ItemScrollController();

  @override
  void initState() {
    super.initState();
    while(titles.length<30) {
      titles.add('Some Text ${titles.length}');
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Expanded(
                child: ScrollablePositionedList.builder(
                  itemScrollController: scrollController,
                  itemBuilder: (context, index) => Container(
                    alignment: Alignment.bottomCenter,
                    padding: EdgeInsets.symmetric(vertical: 10),
                    child: Text(titles[index]),
                  ),
                  itemCount: titles.length,
                )
            ),
            Divider(),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: <Widget>[
                OutlineButton(
                  child: Text('1.Jump to last item'),
                  onPressed: () {
                    scrollController.jumpTo(index: titles.length-1);
                  },
                ),
                OutlineButton(
                  child: Text('2.Delete the last item'),
                  onPressed: () {
                    titles.removeAt(titles.length-1);
                    setState(() {

                    });
                  },
                ),
              ],
            )
          ],
        ),
      ), 
    );
  }
}

[AurelianTimu]

@iKrupp

I got it working like follows :

I have a variable _deletedItems that I use to keep track of the elements that are removed from entityList. When an element is removed, I just increment _deletedItems.
When index becomes equal to entityList.length and _deletedItems != 0 it means that an element was removed from the list, hence a Container() is returned.

In my case, the code looks something like this :

....

  @override
  void didUpdateWidget(CustomStatefulWidget oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.entityList.length > widget.entityList.length) {
      // An item was removed/deleted from the list
        _deletedItems += 1;
    }
    entityList = widget.entityList;
  }
....
itemBuilder: (BuildContext context, int index) {
     if (index <= entityList.length ) {
      final entity = entityList[index];
      return CustomWidget(..); 
    } else if (index == entityList.length && _deletedItems == 0) {
      final entity = entityList[index];
      return CustomWidget(..); 
    } else {
      return Container()
    }
 },
....

[arteminthesky]

@vabawen thank you for example! Could you also duplicate it here: #42

[arteminthesky]

@AurelianTimu this was my first thought - returning the stub to an inaccessible index. (for this, it seems, you do not even need to count the number of deleted elements). However, I tried Offstage instead of a container. I will try the container, however this is still a workaround. It would be better if this were fixed on the side of the plugin

[AurelianTimu]

Correct, you dont need the exact count of deleted items in this case. I am using the count for a different purpose. I forgot to mention it in my comment.