Question 187326 in Flutter Question posted in
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Flutter – How to await Map<int,Future<T>>?

I’ve a Map<int, Future<GpxCoordinates>> in which the int key is the id of the entity and the future contains the async call to my API to get data for the related entity id.

I need to start all the requests togethers and then await them.

That’s my not working implementation:

try {
      Map<int, Future<GpxCoordinates>> gpxsCoordinatesToFetch = {};

      for (var tourId in event.toursIds) {
        gpxsCoordinatesToFetch[tourId] = gpxRepository.fetchGpxCoordinates(tourId);
      }

      // Problem in the return await type
      final gpxsCoordinates = await Future.wait(gpxsCoordinatesToFetch.values);

      emit(GpxsCoordinatesLoaded(coordinates: gpxsCoordinates));
    } catch (e) {
      debugPrint(e.toString());
      emit(GpxError());
    }

The problem is that the Future.await returns a List<GpxCoordinates> but I need to return a Map<int, GpxCoordinates>. Does it exists a way to obtain the desired Map<int, GpxCoordinates> once all requests have been finished?

Tags:

2

Answers


  1. 0

    You have to somehow connect the received data with the id. This is one of the ways to achieve it:

    try {
  final Map<int, String> values = {};
  final List<Future> futures = [];
  for (var tourId in [1, 2]) {
    futures.add(Future.microtask(() async {
      // Do the call here
      final String value = await Future.value('some value');

      values[tourId] = value;
    }));
  }

  await Future.wait(futures);

  print(values);
} catch (e) {
  // ...
}

    Outputs:
    {1: some value, 2: some value}

    Another one (probably better):

    ...
for (var tourId in [1, 2]) {
  futures.add(
    Future.value('some value').then((value) => values[tourId] = value),
  );
}
...
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  2. 0

    Replace

      // Problem in the return await type
  final gpxsCoordinates = await Future.wait(gpxsCoordinatesToFetch.values);

    with

    Map<int,GpxCoordinates> gpxsCoordinates = {};
for (final mapEntry in gpxsCoordinatesToFetch.entries) {
   final key = mapEntry.key;
   final futureVal = mapEntry.value;
   gpxsCoordinates[key] = await futureVal;
}
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