Intercepting mouse scrolling when nesting scroll views

main.dart

import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';

void main() => runApp(App());

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(),
        body: ListView.builder(
          itemCount: 30,
          itemBuilder: (_, int index) {
            return SizedBox(
              height: 300,
              child: Center(
                child: Listener(
                  onPointerSignal: (event) {
                    // Claims the pointer signal when the inner ListView does
                    // not, prevents the outer from claiming it.
                    GestureBinding.instance.pointerSignalResolver.register(
                      event,
                      (event) {},
                    );
                  },
                  child: Container(
                    height: 200,
                    width: 200,
                    color: Colors.purple[100],
                    child: ListView.builder(
                      itemCount: 20,
                      itemBuilder: (_, int index) => Text('Index $index'),
                    )
                  ),
                ),
              ),
            );
          }
        ),
      ),
    );
  }
}