Multi future

multi_future_builder.dart

import 'package:flutter/widgets.dart';
import 'multi_future_listener.dart';

class MultiFutureBuilder<T> extends StatefulWidget {
  final List<Future<T>> futures;
  final Widget Function(BuildContext context, AsyncSnapshot<List<T>> snapshot)
      builder;

  const MultiFutureBuilder({
    super.key,
    required this.futures,
    required this.builder,
  });

  @override
  State createState() => _MultiFutureBuilderState<T>();
}

class _MultiFutureBuilderState<T> extends State<MultiFutureBuilder<T>> {
  late List<Future<T>> _futures;
  late AsyncSnapshot<List<T>> _snapshot;

  @override
  void initState() {
    super.initState();
    _futures = widget.futures;

    // Initialize snapshot
    _snapshot = AsyncSnapshot<List<T>>.withData(ConnectionState.none, []);

    // Listen to the futures
    MultiFutureListener(
      futures: _futures,
      onComplete: (results) {
        setState(() {
          _snapshot = AsyncSnapshot.withData(ConnectionState.done, results);
        });
      },
      onError: (error) {
        setState(() {
          _snapshot = AsyncSnapshot.withError(ConnectionState.done, error);
        });
      },
    );
  }

  @override
  Widget build(BuildContext context) => widget.builder(context, _snapshot);
}

multi_future_listener.dart

class MultiFutureListener<T> {
  final List<Future<T>> futures;
  final void Function(List<T> results) onComplete;
  final void Function(Object error)? onError;

  MultiFutureListener({
    required this.futures,
    required this.onComplete,
    this.onError,
  }) {
    List<T> results = List.filled(futures.length, null as T);
    int completedCount = 0;

    futures.asMap().forEach((index, future) {
      future.then((result) {
        results[index] = result;
        completedCount++;
        if (completedCount == futures.length) {
          onComplete(results);
        }
      }).catchError((error) {
        if (onError != null) {
          onError!(error);
        }
      });
    });
  }
}