如何向PreviewProvider添加GeometryProxy

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart' show kIsWeb;
import 'package:flutter/services.dart';
import 'package:flutter/material.dart' as prefix0;
import 'package:flutter/foundation.dart' as prefix1;

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: MaterialPreviewBuilder(
            builder: (context, previewContext) {
              return Container(
                width: 200,
                height: 200,
                color: Colors.blue,
                child: GeometryProxy(
                  geometry: BoxGeometry(
                    size: Size(100, 100),
                    alignment: Alignment.center,
                  ),
                  builder: (context, geometry) {
                    return Container(
                      width: geometry.size.width,
                      height: geometry.size.height,
                      color: Colors.red,
                    );
                  },
                ),
              );
            },
          ),
        ),
      ),
    );
  }
}