Reputation: 983
I am trying to make an Infinite list using flutter bloc.
I have taken reference from here: https://github.com/felangel/bloc/blob/926029cae2d7614d38b5a9a8952e36bb59054b02/examples/github_search/common_github_search/lib/src/github_search_bloc/github_search_bloc.dart#L15
According to this post, to add a delay between two events so that api doesn't get spammed, you need to override transformEvents
and add debounce to events like this:
@override
Stream<GithubSearchState> transformEvents(
Stream<GithubSearchEvent> events,
Stream<GithubSearchState> Function(GithubSearchEvent event) next,
) {
return (events as Observable<GithubSearchEvent>)
.debounceTime(
Duration(milliseconds: 300),
)
.switchMap(next);
}
Problem I am facing is that the Observable has been deprecated by RxDart and I am not sure how to accomplish the above requirement.
Upvotes: 4
Views: 18010
Reputation: 14083
I had a similar issue and I could solve it by adding the below imports
import 'package:stream_transform/stream_transform.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
Then we can provide a custom EventTransformer to change the way the Bloc processes incoming events.
EventTransformer<T> debounce<T>(Duration duration) {
return (events, mapper) => events.debounceTime(duration).flatMap(mapper);
}
Now we would probably want to debounce the requests to the backend to avoid getting rate-limited and cut down on cost/load on the backend.
CounterBloc() : super(0) {
on<Increment>(
(event, emit) => emit(state + 1),
/// Apply the custom `EventTransformer` to the `EventHandler`.
transformer: debounce(const Duration(milliseconds: 300)),
);
}
Note: I was using flutter_bloc: ^8.1.1
Upvotes: 1
Reputation: 459
Since bloc
8.0.0 the syntax changed and you need to pass it as a transformer to the on
function. Apart from the debouncing you should think about concurrency. To combine sequential processing with a debounce, you can provide the following function:
import 'package:rxdart/rxdart.dart';
//...
on<GithubSearchEvent>(
(event, emit) {},
transformer: (events, mapper) {
return events.debounceTime(const Duration(milliseconds: 300)).asyncExpand(mapper);
},
);
You can create a reusable transformer as a top-level function like this:
EventTransformer<Event> debounceSequential<Event>(Duration duration) {
return (events, mapper) => events.debounceTime(duration).asyncExpand(mapper);
}
and use it like this:
on<GithubSearchEvent>(
(event, emit) {},
transformer: debounceSequential(const Duration(milliseconds: 300)),
);
Upvotes: 23
Reputation: 196
I cannt add comment to @user2220771 cause my reputation is too low.
This will not work:
EventTransformer<Event> debounceTransformer<Event>(Duration duration) {
return (events, mapper) => events.debounceTime(duration);
}
you have to switch map as:
EventTransformer<Event> debounceTransformer<Event>(Duration duration) {
return (events, mapper) {
return events.debounceTime(duration).switchMap(mapper);
};
}
Upvotes: 8
Reputation: 983
I found the solution.
@override
Stream<Transition< GithubSearchEvent, GithubSearchState >> transformEvents(
Stream< GithubSearchEvent > events, transitionFn) {
return events
.debounceTime(const Duration(milliseconds: 300))
.switchMap((transitionFn));
}
Upvotes: 12