Streams In Flutter

Streams In Flutter are like pipes. If you put a value on one end and have a listener on the other end, that listener will pick it up. A stream can have multiple listeners, all of which get the same value when they enter the pipeline. Use a StreamController to put values into a stream.Streams provide an asynchronous sequence of data.

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Type of Streams : There are two type of streams.

Single Subscription: There could be a maximum of one listener to this stream.
Broadcast: There could be the infinite number of the listener to this stream.

1. Single Subscription Stream:

A single subscription stream works great when you’re only using certain streams on a screen. You can only listen to one subscription stream once. It won’t start generating events until there is a listener, and will stop sending events when the listener stops listening, even if the source of the event can provide more data.

A single subscription stream is useful for file downloads or single operations. For example, a widget can subscribe to a stream to get value updates.

import 'dart:convert';
import 'dart:async';
  
// Initializing a stream controller
StreamController<String> controller = StreamController<String>();
  
// Creating a new stream through the controller
Stream<String> stream = controller.stream;
  
void main() {
  
    // Setting up a subscriber to listen for any events sent on the stream
    StreamSubscription<String> subscriber = stream.listen((String data) {
        print(data);
    },
    onError: (error) {
        print(error);
    },
    onDone: () {
        print('Stream closed!');
    });
  
    // Adding a data event to the stream with the controller
    controller.sink.add('Hello!');
  
    // Adding an error event to the stream with the controller
    controller.addError('Hi!');
  
    // Closing the stream with the controller
    controller.close();
  
}

import 'dart:convert';

import 'dart:async';

// Initializing a stream controller

StreamController<String> controller = StreamController<String>();

// Creating a new stream through the controller

Stream<String> stream = controller.stream;

void main() {

// Setting up a subscriber to listen for any events sent on the stream

StreamSubscription<String> subscriber = stream.listen((String data) {

print(data);

onError: (error) {

print(error);

onDone: () {

print('Stream closed!');

});

// Adding a data event to the stream with the controller

controller.sink.add('Hello!');

// Adding an error event to the stream with the controller

controller.addError('Hi!');

// Closing the stream with the controller

controller.close();

}

2. Broadcast streams:

If you need multiple parts of your app to access the same stream, use broadcast streams instead. A broadcast stream can have any number of listeners. Occurswhen an event is ready, with or without listeners. To create a broadcast stream, simply call asBroadcastStream() on an existing single subscription stream.

import 'dart:convert';
import 'dart:async';

// Initializing a stream controller for a broadcast stream
StreamController<String> controller = StreamController<String>.broadcast();

// Creating a new broadcast stream through the controller
Stream<String> stream = controller.stream;

void main() {
	// Setting up a subscriber to listen for any events sent on the stream
	StreamSubscription<String> subscriber1 = stream.listen((String data) {
		print('Subscriber1: ${data}');
	},
	onError: (error) {
		print('Subscriber1: ${error}');
	},
	onDone: () {
		print('Subscriber1: Stream closed');
	});

	// Setting up another subscriber to listen for any events sent on the stream
	StreamSubscription<String> subscriber2 = stream.listen((String data) {
		print('Subscriber2: ${data}');
	},
	onError: (error) {
		print('Subscriber2: ${error}');
	},
	onDone: () {
		print('Subscriber2: Stream closed');
	});

	// Adding a data event to the stream with the controller
	controller.sink.add('Hello!');

	// Adding an error event to the stream with the controller
	controller.addError('Hi!');

	// Closing the stream with the controller
	controller.close();
}

import 'dart:convert';

import 'dart:async';

// Initializing a stream controller for a broadcast stream

StreamController<String> controller = StreamController<String>.broadcast();

// Creating a new broadcast stream through the controller

Stream<String> stream = controller.stream;

void main() {

// Setting up a subscriber to listen for any events sent on the stream

StreamSubscription<String> subscriber1 = stream.listen((String data) {

print('Subscriber1: ${data}');

onError: (error) {

print('Subscriber1: ${error}');

onDone: () {

print('Subscriber1: Stream closed');

});

// Setting up another subscriber to listen for any events sent on the stream

StreamSubscription<String> subscriber2 = stream.listen((String data) {

print('Subscriber2: ${data}');

onError: (error) {

print('Subscriber2: ${error}');

onDone: () {

print('Subscriber2: Stream closed');

});

// Adding a data event to the stream with the controller

controller.sink.add('Hello!');

// Adding an error event to the stream with the controller

controller.addError('Hi!');

// Closing the stream with the controller

controller.close();

}

Conclusion:

I hope you get the rough idea to how to use Stream in Flutter. For reference you can also check here.

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Thanks for reading…

Mohit Kumar 25 April 2023

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Streams In Flutter

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