如何让StreamBuilder停止监听事件

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

class MyStreamBuilder extends StatefulWidget {
  @override
  _MyStreamBuilderState createState() => _MyStreamBuilderState();
}

class _MyStreamBuilderState extends State<MyStreamBuilder> {
  StreamController<int> _streamController;
  StreamSubscription<int> _subscription;
  int _data;

  @override
  void initState() {
    super.initState();
    _streamController = StreamController<int>();
    _subscription = _streamController.stream.listen((data) {
      setState(() {
        _data = data;
      });
    });
  }

  @override
  void dispose() {
    _subscription.cancel(); // 取消订阅，停止监听事件
    _streamController.close(); // 关闭流
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('StreamBuilder Example'),
      ),
      body: Center(
        child: StreamBuilder<int>(
          stream: _streamController.stream,
          builder: (context, snapshot) {
            if (snapshot.hasData) {
              return Text('Data: ${snapshot.data}');
            } else {
              return Text('No data');
            }
          },
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _streamController.sink.add(42); // 向流中添加数据
        },
        child: Icon(Icons.add),
      ),
    );
  }
}