颤动StreamBuilder错误

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('StreamBuilder Example')),
        body: StreamBuilderExample(),
      ),
    );
  }
}

class StreamBuilderExample extends StatefulWidget {
  @override
  _StreamBuilderExampleState createState() => _StreamBuilderExampleState();
}

class _StreamBuilderExampleState extends State<StreamBuilderExample> {
  final StreamController<int> _controller = StreamController<int>();
  int _counter = 0;

  @override
  void initState() {
    super.initState();
    // 控制更新频率
    Timer.periodic(Duration(seconds: 1), (Timer t) {
      _controller.add(_counter++);
    });
  }

  @override
  void dispose() {
    _controller.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: StreamBuilder<int>(
        stream: _controller.stream,
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            return Text('Counter: ${snapshot.data}');
          } else {
            return CircularProgressIndicator();
          }
        },
      ),
    );
  }
}

Stream<int> distinctStream(Stream<int> source) async* {
  Set<int> seen = {};
  await for (int value in source) {
    if (!seen.contains(value)) {
      seen.add(value);
      yield value;
    }
  }
}

StreamBuilder<int>(
  stream: distinctStream(_controller.stream),
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return Text('Counter: ${snapshot.data}');
    } else {
      return CircularProgressIndicator();
    }
  },
);