[Dart] Data Communication with Stream

The Stream can guarantee the order of the data.

Stream acts like a queue.

Stream Example

Let's take a look at a simple example.

import 'dart:async';
    
void main() async {
  var stream = streamSend(10);
  var sum = await streamReceive(stream);
  print('Sum: $sum');
}

Stream<int> streamSend(int to) async* {
  for (int i = 1; i <= to; i++) {    
    print('Sent: $i');
    yield i;
  }
}

Future<int> streamReceive(Stream<int> stream) async {
  var sum = 0;
  await for (var value in stream) {
    print('Received: $value');
    sum += value;
  }
  return sum;
}

This example sends integer data from 1 to 10 asynchronously using yield.

And, it receives the data and accumulates it.

Properties and Methods of Stream

The Stream has useful methods.

void main() {
  var stream = Stream.fromIterable([1, 2, 3, 4, 5]);
  stream.first.then((value) => print('first: $value'));
  // 1

  stream = Stream.fromIterable([1, 2, 3, 4, 5]);
  stream.last.then((value) => print('last: $value'));
  // 5

  stream = Stream.fromIterable([1, 2, 3, 4, 5]);
  stream.isEmpty.then((value) => print('isEmpty: $value'));
  // false

  stream = Stream.fromIterable([1, 2, 3, 4, 5]);
  stream.length.then((value) => print('length: $value'));
  // 5
}

As you can see from the above example, every time I use the stream, I created stream data.

It is because the stream data is removed once it is used.

fromIterable(Iterable<T> elements)

This method is one of the constructors of the Stream class.

This method creates stream data from iterable data.

Future<T> first

This property contains the first element of the stream.

Future<T> last

This property contains the last element of the stream.

Future<bool> isEmpty

This property contains whether the stream is empty.

Future<int> length

This property contains the number of elements in the stream.