> For the complete documentation index, see [llms.txt](https://eece.gitbook.io/mist-innovation-club-flutter-course-1/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eece.gitbook.io/mist-innovation-club-flutter-course-1/dart-fundamentals-3/advanced-asynchronous-programming/streams.md).

# Streams

## Basics of Streams 

{% embed url="<https://youtu.be/ObxHoXd8x3o>" %}

```dart
import 'dart:async';

void main() {
  // Streams
  var numberStream = NumberGenerator().stream;

  numberStream.listen((data) {
    print(data);
  });
}

class NumberGenerator {
  NumberGenerator() {
    Timer.periodic(Duration(seconds: 1), (t) {
      controller.sink.add(count);

      count++;
    });
  }

  var count = 1;

  final controller = StreamController<int>();

  Stream<int> get stream => controller.stream;
}



```

![](/files/-MHOSnP_yc5ogFMvkVi5)

{% hint style="success" %}
Stream emits  an asynchronous sequence of data.
{% endhint %}

## Types of Stream&#x20;

{% embed url="<https://www.youtube.com/watch?v=V9Qpz9Ar2FI>" %}

There are two types of streams in dart :-&#x20;

* [x] Single Subscription Stream
* [x] Broadcast Stream

{% tabs %}
{% tab title=" Multiple subscription on single subscription stream " %}

```dart
// This will show an error
import 'dart:async';

void main() {
  // Streams
  var numberStream = NumberGenerator().stream;

  final subscription1 = numberStream.listen((data) {
    print(data);
  });

  final subscription2 = numberStream.listen((data) {
    print(data);
  });
}

class NumberGenerator {
  NumberGenerator() {
    Timer.periodic(Duration(seconds: 1), (t) {
      controller.sink.add(count);

      count++;
    });
  }

  var count = 1;

  final controller = StreamController<int>();

  Stream<int> get stream => controller.stream;
}

```

{% endtab %}

{% tab title="Broadcast Stream with multiple subscription" %}

```dart


import 'dart:async';

void main() {
  // Streams
  var numberStream = NumberGenerator().stream.asBroadcastStream();

  final subscription1 = numberStream.listen((data) {
    print(data);
  });

  final subscription2 = numberStream.listen((data) {
    print(data);
  });
}

class NumberGenerator {
  NumberGenerator() {
    Timer.periodic(Duration(seconds: 1), (t) {
      controller.sink.add(count);

      count++;
    });
  }

  var count = 1;

  final controller = StreamController<int>();

  Stream<int> get stream => controller.stream;
}

```

{% endtab %}
{% endtabs %}

{% tabs %}
{% tab title="Single Subscription Stream " %}
![](/files/-MHOiEgm9Qk9BDEqgHjI)
{% endtab %}

{% tab title="Broadcast Stream" %}
![](/files/-MHOiLn1xrRHSLAU8egN)
{% endtab %}
{% endtabs %}

## Error Handling in Stream

{% embed url="<https://youtu.be/VaGl3rdp4SM>" %}

```dart
import 'dart:async';

void main() {
  // Streams
  var numberStream = NumberGenerator().stream;

  final subscription1 = numberStream.listen((data) {
    print(data);
  }, onError: (err) {
    //logic for error handling
    print("$err, Error detected !");
  }, cancelOnError: true);
}

class NumberGenerator {
  NumberGenerator() {
    Timer.periodic(Duration(seconds: 1), (t) {
      if (count == 5) {
        controller.sink.addError("Error !!!!");
      }
      controller.sink.add(count);

      count++;
    });
  }

  var count = 1;

  final controller = StreamController<int>();

  Stream<int> get stream => controller.stream;
}

```

![](/files/-MHPJ95qKh2CQ6ZVWNUk)

## Manipulating  Streams

{% embed url="<https://youtu.be/uFw88sFu14s>" %}

```dart
import 'dart:async';

void main() {
  // Streams
  var numberStream = NumberGenerator().stream;

  final subscription1 =
      numberStream.map((i) => i * 3).where((i) => i % 2 == 0).listen((data) {
    print(data);
  });
}

class NumberGenerator {
  NumberGenerator() {
    Timer.periodic(Duration(seconds: 1), (t) {
      controller.sink.add(count);

      count++;
    });
  }

  var count = 1;

  final controller = StreamController<int>();

  Stream<int> get stream => controller.stream;
}

```

![](/files/-MHWb_lrZYEWbf4tfkMM)

## Creating Streams

{% embed url="<https://youtu.be/kN6YItCf3KY>" %}

![](/files/-MHWk8hvmBr_GRdMJOE5)

If you want to explore more about Streams : -

{% embed url="<https://dart.dev/tutorials/language/streams>" %}

{% embed url="<https://api.dart.dev/stable/2.9.3/dart-async/Stream-class.html>" %}


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