Can I use a FutureBuilder with a value of the type FutureOr?

Question

I was wondering if there is a way how I can use a Future Builder together with a FutureOr<T> typed future-parameter?

Answer 1

The simplest way would be to always convert the FutureOr<T> to a Future<T>. The Future class has numerous constructors that can do that:

• Future<T>.new
• Future<T>.microtask
• Future<T>.sync
• Future<T>.value

Any of them should work, but if I'd use Future<T>.value or Future<T>.new:

FutureBuilder(future: Future.value(maybeFuture), ...)

If that isn't desirable (waiting on a Future<T> created from an existing T entails an extra iteration of the event loop), then it's pretty simple to create your own FutureOrBuilder widget that's like a FutureBuilder but that invokes its AsyncWidgetBuilder callback synchronously if possible:

class FutureOrBuilder<T> extends StatelessWidget {
  final FutureOr<T>? futureOrValue;

  final T? initialData;

  final AsyncWidgetBuilder<T> builder;

  const FutureOrBuilder({
    super.key,
    FutureOr<T>? future,
    this.initialData,
    required this.builder,
  }) : futureOrValue = future;

  @override
  Widget build(BuildContext context) {
    final futureOrValue = this.futureOrValue;
    if (futureOrValue is T) {
      return builder(
        context,
        AsyncSnapshot.withData(ConnectionState.done, futureOrValue),
      );
    } else {
      return FutureBuilder(
        future: futureOrValue,
        initialData: initialData,
        builder: builder,
      );
    }
  }
}