CODEWITHSUNDEEP
dartflutter
Daniel Oliveira
Daniel Oliveira

Reputation: 8953

How to transmit an error through async* in Dart?

In flutter we make use of the StreamBuilder with receives a Stream e gives us a Snapshot object that contains "data" but also contains "error" objects.

I want to make a function with async* that yields data but due to some conditions it can yield also some errors. How can I achieve that in Dart?

Stream<int> justAFunction() async* {
  yield 0;

  for (var i = 1; i < 11; ++i) {
    await Future.delayed(millis(500));
    yield i;
  }

  yield AnyError(); <- I WANT TO YIELD THIS!
}

And then, in the StreamBuilder:

StreamBuilder(
            stream: justAFunction(),
            builder: (BuildContext context, AsyncSnapshot<RequestResult> snapshot) {
              return Center(child: Text("The error tha came: ${snapshot.error}")); <- THIS SHOULD BE THE AnyError ABOVE!
            },
          )

Upvotes: 9

Views: 1759

Answers (2)

BambinoUA
BambinoUA

Reputation: 7100

Below the working example:

void main() {
  justAFunction().listen((i) => print(i), onError: (error) => print(error));
}


Stream<int> justAFunction() async* {
  yield 0;

  for (var i = 1; i < 3; ++i) {
    await Future.delayed(Duration(milliseconds:500));
    yield i;
  }

  yield* Stream.error('error is here'); <- Yield error!
}

Upvotes: 3

R&#233;mi Rousselet
R&#233;mi Rousselet

Reputation: 276997

Simply throw

Stream<int> foo() async* {
  throw FormatException();
}

Upvotes: 12

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