如何在流到达StreamBuilder之前进行转换？

import 'dart:async';

StreamTransformer<int, String> createStreamTransformer() {
  return StreamTransformer<int, String>.fromHandlers(
    handleData: (int value, EventSink<String> sink) {
      // 在这里进行数据转换，这里的例子是将整数转换为字符串
      sink.add(value.toString());
    },
  );
}

void main() {
  final streamController = StreamController<int>();
  
  // 创建一个转换器
  final transformer = createStreamTransformer();
  
  // 应用转换器并获取转换后的流
  final transformedStream = streamController.stream.transform(transformer);
  
  // 通过StreamBuilder使用转换后的流
  final streamBuilder = StreamBuilder<String>(
    stream: transformedStream,
    builder: (context, snapshot) {
      if (snapshot.hasData) {
        return Text(snapshot.data!);
      } else {
        return CircularProgressIndicator();
      }
    },
  );
  
  // 添加数据到原始流
  streamController.add(42);
  
  // 运行应用
  runApp(MyApp(streamBuilder));
}

class MyApp extends StatelessWidget {
  final StreamBuilder<String> streamBuilder;
  
  MyApp(this.streamBuilder);
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Stream Transformation')),
        body: Center(child: streamBuilder),
      ),
    );
  }
}