Lære Consuming Streams with await for

When working with asynchronous data in Dart, Streams allow you to receive a sequence of values over time. To consume these values in an easy-to-read, sequential manner, you can use the await for syntax inside an async function. This lets you process each event from the Stream as it arrives, pausing execution until the next value is available.

The await for loop works much like a regular for loop, but it waits for each item from the Stream asynchronously. This means your code remains simple and readable, even when dealing with values that might arrive at unpredictable intervals.

In contrast, the listen method attaches a callback function to the Stream. The callback is called every time the Stream emits a value, but your code continues running without waiting for those events. This can make it harder to write code that depends on the order or timing of Stream events, especially if you need to perform asynchronous operations in sequence.

Use await for when you want to handle each Stream event in order, waiting for each one before moving to the next. Use listen when you want to react to events as they arrive, without blocking the rest of your code.

main.dart


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// main.dart
// Demonstrates using await for to process events from a Stream of strings.

Stream<String> generateMessages() async* {
  yield "Hello";
  await Future.delayed(Duration(milliseconds: 500));
  yield "from";
  await Future.delayed(Duration(milliseconds: 500));
  yield "the";
  await Future.delayed(Duration(milliseconds: 500));
  yield "Stream!";
}

Future<void> main() async {
  print("Starting to receive messages...");
  await for (var message in generateMessages()) {
    print("Received: $message");
  }
  print("All messages received.");
}

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Suggested prompts:

Can you show an example of using `await for` with a Stream in Dart?

What are some common use cases for `await for` versus `listen`?

Are there any limitations or caveats when using `await for` with Streams?

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main.dart


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// main.dart
// Demonstrates using await for to process events from a Stream of strings.

Stream<String> generateMessages() async* {
  yield "Hello";
  await Future.delayed(Duration(milliseconds: 500));
  yield "from";
  await Future.delayed(Duration(milliseconds: 500));
  yield "the";
  await Future.delayed(Duration(milliseconds: 500));
  yield "Stream!";
}

Future<void> main() async {
  print("Starting to receive messages...");
  await for (var message in generateMessages()) {
    print("Received: $message");
  }
  print("All messages received.");
}

Alt var klart?

Takk for tilbakemeldingene dine!

Seksjon 3. Kapittel 2