[BUG] Map fails to reinitialize while in ListView

[Zverik]

When you put the FlutterMap inside a ListView, it can be hidden and then added anew. And it fails, because it sets a new state for a map controller, which is already initialized. Testing code is below: it adds 30 lines of text after the map. Scroll down and then back up again to see the error.

Mapybe mapController needs to be disposed properly?

Flutter_map 1.1.0, Flutter 3, Dart 2.17.

import 'package:flutter_map/flutter_map.dart';
import 'package:latlong2/latlong.dart' show LatLng;

void main() {
  runApp(const MaterialApp(
    title: 'Flutter Demo',
    home: MyHomePage(),
  ));
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Map in a ListView'),
      ),
      body: ListView(children: [
        SizedBox(
          height: 100.0,
          child: FlutterMap(
            options: MapOptions(
              center: LatLng(50, 30),
              zoom: 13,
              allowPanningOnScrollingParent: false,
            ),
            layers: [
              TileLayerOptions(
                urlTemplate: 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
              ),
            ],
          ),
        ),
        for (int i = 1; i < 30; i++)
          Padding(
            padding: const EdgeInsets.all(20.0),
            child: Center(child: Text('Line $i', style: const TextStyle(fontSize: 20))),
          ),
      ]),
    );
  }
}

[ibrierley]

I think mapController is disposed of ok...

However, I suspect removing final from late final MapState mapState; in flutter_map_state.dart would do it...not sure if there's any implications there

[JaffaKetchup]

As this as now had two reports, I'm going to remove the 'needs verification' label.

If you can try @ibrierley's suggestion @Zverik, that would be great :)

[Zverik]

I think @ibrierley's suggestion does not make sense, because it's the final field initializing in initState(), that checks out. The error was this:

Flutter: LateInitializationError: Field '_state@954051772' has already been initialized.

#0      LateError._throwFieldAlreadyInitialized (dart:_internal-patch/internal_patch.dart:194:5)
#1      MapControllerImpl._state= (package:flutter_map/src/map/map.dart:25:23)
#2      MapControllerImpl.state= (package:flutter_map/src/map/map.dart:29:5)
#3      FlutterMapState.initState (package:flutter_map/src/map/flutter_map_state.dart:38:19)
#4      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4942:57)
#5      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4781:5)
#6      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3817:16)
#7      Element.updateChild (package:flutter/src/widgets/framework.dart:3551:18)
...

It can be fixed by removing the final keyword from lib/src/map/map.dart:25. And it is indeed weird, having a final property with a non-scoped setter. I have tested it, and it worked.

[ibrierley]

(Not sure if you meant it makes sense or doesn't make sense). However, I don't necessarily think it makes sense either way, even if it works :D. That's why I mentioned the implications.

The preferred way I guess would be to use your own mapController.

I suspect the problem with removing final, is maybe it stops one error, but previously I think the mapState was disposed (I assume)...are those disposed elements (any streams etc) reinstated, or is it in a slightly broken state, because other things weren't handled ? Do MapEvents and things like that still work correct...

[JaffaKetchup]

Yeah it appears streams are still broken. I made a review on #1293 with a screenshot of the issue.