Future.wait possible in future builder when futures return different value types?

Question

I have found answers how to wait for 2 different futures when building widgets, but these were of the same type. Example from here:

But is there also a possibility if firstFuture() and secondFuture() return different value types - eg int and String (or different classes as in my use case)? The bool in AsyncSnapshot<List<bool>> snapshot is a challenge to me...

FutureBuilder(
    future: Future.wait([
         firstFuture(), // Future<bool> firstFuture() async {...}
         secondFuture(),// Future<bool> secondFuture() async {...}
         //... More futures
    ]),
    builder: (
       context, 
       // List of booleans(results of all futures above)
       AsyncSnapshot<List<bool>> snapshot, 
    ){

       // Check hasData once for all futures.
       if (!snapshot.hasData) { 
          return CircularProgressIndicator();
       }

       // Access first Future's data:
       // snapshot.data[0]

       // Access second Future's data:
       // snapshot.data[1]

       return Container();

    }
);

I also found another answer with different types, but this apples to functions not classes

List<Foo> foos;
List<Bar> bars;
List<FooBars> foobars;

await Future.wait<void>([
  downloader.getFoos().then((result) => foos = result),
  downloader.getBars().then((result) => bars = result),
  downloader.getFooBars().then((result) => foobars = result),
]);

processData(foos, bars, foobars);

score 2 · Accepted Answer · answered Sep 14 '20 at 09:46

Well, you can always use Object as the lowest common return value of those two methods:

Future.wait<Object>([firstFuture(), secondFuture()])

But you will have to cast the entries of the resulting List<Object> back to what you think they should be. Not perfect, but it would work.

Personally, I like the method you already discovered a bit more, return only the bare minimum future, a Future<void> and have it write to the respective variables inside the method. That is not perfect either, but it keeps the type safety.

score 1 · Answer 2 · edited Mar 21 '23 at 06:18

Below answer might help you

Use FutureGroup inside the package

dependencies: async: ^2.4.1

Code:

void main()  {
  Future<String> future1 = getData(2);
  Future<String> future2 = getData(4);
  Future<String> future3 = getData(6);
  FutureGroup futureGroup = FutureGroup();
  futureGroup.add(future1);
  futureGroup.add(future2);
  futureGroup.add(future3);
  futureGroup.close();
  futureGroup.future.then((value) => {print(value)});
}

Future<String> getData(int duration) async {
  await Future.delayed(Duration(seconds: duration)); //Mock delay
  return "This a test data";
}

Output:

I/flutter ( 5866): [This a test data, This a test data, This a test data] // Called after 6 seconds.

Future.wait possible in future builder when futures return different value types?

2 Answers2