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.
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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.
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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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