Gain insights into Dart's object-oriented features, explore extensions, enums, mixins, and asynchronous programming. Discover hands-on code practice to confidently apply Dart in your projects.

dart.tar.gz

dart2_7

Dart is a fully object-oriented, class-based, simple, and clean language. Google’s popular mobile framework, Flutter uses Dart language to implement high-quality native applications, so it’s recommended that you understand Flutter before beginning this course.

In this course, you will dive deep into Dart 2 language features while using interactive hands-on code playgrounds. This course will help you become confident with Dart extensions, enums, mixins, generics, libraries, asynchronous programming, class variables, callable classes, and generator functions.

By the end of this course, you will have a strong understanding of Dart principles, and you’ll be ready to start using this powerful language in your own projects.

Developing Web Applications with Dart

# Types of Streams

There are two types of Streams that one can be used to carry out the asynchronous operations.

1. **Single Subscription**

   Single subscription streams are meant to deliver events in order. These types of streams are used when the order of events received matters; like reading a file. Such types of Streams can only be listened to once. Attempting to listen to them again will throw an exception.

2. **Broadcast (Multiple subscribers)**

    Broadcast streams are intended to deliver events to their subscribers. Once subscribed, any subscriber can2 start listening to events. A Broadcast stream can be listened to multiple times.

**Note:** A Single Subscription Stream can be converted into a broadcast Stream by using the [`asBroadcastStream()`](https://api.flutter.dev/flutter/dart-async/Stream/asBroadcastStream.html) method.

You will learn more about these two approaches in upcoming lessons.

# Subscribing to a Stream

In this section, you will learn two approaches to subscribe to a stream:

1. Using the `listen()` method

2. Using a Subscription's handler


Let's generate a stream to demonstrate both types of subscriptions. This stream will generate numbers 1 through 5 and will throw an exception when it encounters the number 5. We'll use `createNumberStreamWithException()` to generate a Stream for the examples in this lesson. 

```
//This will generate a stream and return a reference to it.
Stream<int> createNumberStreamWithException(int last) async* {
  for (int i = 1; i <= last; i++) {
    if (i == 5) {
      throw new Exception("Demo exception when accessing 5th number");
    }
    yield i; //to be able to send spaced out events
  }
}
```

## Using `listen()`

The example below uses the [`listen()`](https://api.flutter.dev/flutter/dart-async/Stream/listen.html) method.

In this example, `createNumberStreamWithException()` is used to generate a Stream. The Stream is listened to and prints all numbers on the console. It prints errors in the `onError:` block. The `onDone:` block is executed when the stream is done with its events.

The `subscribeUsingListen()` is executed in `main()` method.

In this lesson, you will learn about the types of Streams.

Introduction

Dart Extensions

Dart Enums

Dart Mixins

Dart Generics

Dart Libraries

Asynchronous Programming In Dart

Miscellaneous

Next Steps

Types of Streams

Types of Streams