How to easily cancel streams in dart/flutter
Canceling streams is a very good practice, but how do you do it as easy as possible ?
Well we should follow the approach from RX with the dispose bag and create a very simple class which we will be able to mixin with any class we have, let’s call it DisposableWidget ... as everything in flutter is a widget :
class DisposableWidget {
List<StreamSubscription> _subscriptions = [];
void cancelSubscriptions() {
_subscriptions.forEach((subscription) {
subscription.cancel();
});
}
void addSubscription(StreamSubscription subscription) {
_subscriptions.add(subscription);
}
}easy… now let’s create a extension for the StreamSubscription class, which is returned every time we listen to a stream :
extension DisposableStreamSubscriton on StreamSubscription {
void canceledBy(DisposableWidget widget) {
widget.addSubscription(this);
}
}easy… now let’s see how we can use this, here is an example with a subscription called from initState :
class CalendarState extends State<Calendar> with DisposableWidget {
@override
void initState() {
super.initState();
_viewModel.setupFromToday();
_viewModel.rebuildStream.listen((rebuild) {
setState(() {
});
}).canceledBy(this);
}@override
void dispose() {
cancelSubscriptions();
super.dispose();
}...
...
...
everything we have to do is mixin the DisposableWidget then call canceledBy(this) after each subscription, and of course remember to call cancelSubscriptions() when disposing the widget… and that’s it, a very nice and simple way to never forget to cancel a subscription.
