CODEWITHSUNDEEP
flutterdartreactive-programmingblocstate-management
Marcin Wróblewski
Marcin Wróblewski

Reputation: 1237

How to throttle events in bloc?

How to throttle events in bloc? Let's say, I want to trigger file save on user input, but perform file system access not more often than once per 100ms?

Example bloc event handler:

on<StoreFile>(_handleStoreEvent);

Upvotes: 3

Views: 2518

Answers (2)

Abid Zaidi
Abid Zaidi

Reputation: 625

You can define a custom EventTransformer which handles how events are processed

EventTransformer<E> throttleDroppable<E>(Duration duration) {
  return (events, mapper) {
    return droppable<E>().call(events.throttle(duration), mapper);
  };
}

Make sure to import package:stream_transform to use the throttle api.

Then simply pass it in the bloc

on<StoreFile>(_handleStoreEvent, transformer: throttleDroppable(Duration(milliseconds: 100)));

For reference see here: Flutter bloc infinite_list example

Upvotes: 1

Marcin Wr&#243;blewski
Marcin Wr&#243;blewski

Reputation: 1237

Each handler have an optional transformer: field which can do throttling (and much more).

Using rxdart you can implement throttling yourself:

on<StoreFile>(
  _handleStoreEvent,
  transformer: (events, mapper) => events.throttleTime(Duration(milliseconds: 100)).switchMap(mapper),
);

I wrote the bloc_event_transformers package to do popular transforms like throttle and debounce to reduce the boilerplate in my apps. It can be used like that:

on<StoreFile>(
  _handleStoreEvent,
  transformer: throttle(Duration(milliseconds: 100)),
);

Upvotes: 9

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