Flutter RxDart switchMap bug答案

【问题标题】：Flutter RxDart switchMap bugFlutter RxDart switchMap bug
【发布时间】：2022-11-09 13:07:47
【问题描述】：

I have a strange bug with Flutter async functions and RxDart (switchMap), here my code:

void main() async {
  Stream periodic = getPeriodicStream();
  Stream mix = periodic.switchMap((parent) {
    return Stream.periodic(const Duration(seconds: 1), (count) {
      return "Result: $parent-$count";
    });
  });
  print(await mix.first);
}

Stream getPeriodicStream() async* {
  Stream periodic = Stream.periodic(const Duration(seconds: 10), (count) {
    print("Periodic stream: $count");
    return "$count";
  });
  //THIS WORK CORRECTLY
  yield* periodic;
  //THIS DOESN'T WORK CORRECTLY
  await for (final period in periodic) {
    yield period;
  }
}

With "yield* periodic;" it works correctly, in the log i see:

flutter: Periodic stream: 0
flutter: Result: 0-0

with "await for (final period in periodic)" that should be the same thing, it doesn't work correctly: it wait for the second stream to return the first stream, log:

flutter: Periodic stream: 0
flutter: Periodic stream: 1
flutter: Result: 0-0

why this strange behavior?

Dartpad: https://dartpad.dev/?id=cc2d1677ad4b05544d10775aaab1fd26

Thanks

标签： flutter dart asynchronous rxdart

【解决方案1】：

I think if you use the below code it will work

import 'dart:async';

Future&lt;void&gt; main() async {
  Stream periodic = getPeriodicStream();
  Stream mix = periodic.switchMap((parent) {
return Stream.periodic(const Duration(seconds: 1), (count) {
  return "Result: $parent-$count";
});
  });
  print(await mix.first);
}

Future&lt;Stream&lt;String&gt;&gt; getPeriodicStream() async* {
  Stream periodic = Stream.periodic(const Duration(seconds: 10), (count) {
print("Periodic stream: $count");
return "$count";
  });
  //THIS WORK CORRECTLY
  yield* periodic;
  //THIS DOESN'T WORK CORRECTLY
  await for (final period in periodic) {
    yield period;
  }
}