CODEWITHSUNDEEP
flutter
Mayank
Mayank

Reputation: 2013

StreamSubscription and StreamBuilder

I want to cancel a stream, and found that a Stream cannot be canceled, but a StreamSubsciption can be canceled. Stream object has a listen() method which

Adds a subscription to this stream.

What actually is a subscription? and how do I use it with StreamBuilder?

From the docs:

A subscription on events from a Stream. When you listen on a Stream using Stream.listen, a StreamSubscription object is returned. The subscription provides events to the listener, and holds the callbacks used to handle the events. The subscription can also be used to unsubscribe from the events, or to temporarily pause the events from the stream.

From what I understand, I think I can use the event and use it to rebuild my widgets. Is it the right way to do it? or is there is a more correct way to do it?

Upvotes: 3

Views: 6603

Answers (1)

Peter Koltai
Peter Koltai

Reputation: 9809

If you are using StreamBuilder, stream subscription and stream cancelling is managed by the framework. The builder method will be called when new snapshot is available, and when the widget is destroyed, stream subscription is cancelled.

As you wrote, you can create your own StreamSubscription with listen() method, and in this case you have to cancel this subscription when you no longer need it, for example in an overridden dispose method. To do so keep track of subscription in a variable or a member, assuming you have a stream in stream variable and MyType is the class which is returned by stream:

StreamSubscription<MyType> myStreamSubscription = stream.listen((value) {
  // add code here
});

Then you can use this to manage the stream:

myStreamSubscription.pause();
myStreamSubscription.resume();
myStreamSubscription.cancel();

Upvotes: 5

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