Check if Future is complete

Question

Before 'm3' you could check if a Future was completed with 'completer.future.isComplete' this seems to be gone. Is there a replacement? or do I need to save it myself then (it seems inside the _CompleterImpl there is still a field '_isComplete' but its not exposed

Answer 1

An alternative to @Cutch's solution is to wrap the Future in a Completer:

Completer<T> wrapInCompleter<T>(Future<T> future) {
  final completer = Completer<T>();
  future.then(completer.complete).catchError(completer.completeError);
  return completer;
}

Future<void> main() async {
  final completer = wrapInCompleter(asyncComputation());
  if (completer.isCompleted) {
    final result = await completer.future;
    // do your stuff
  }
}

This approach is more resourceful since you can both await for the completion asynchronously and check whether the future is completed synchronously.

Answer 2

With M3 Dart, it's best to just use your own flag.

future.whenComplete(() {
  tweenCompleted = true;
});

Dart is a single threaded language so there is no race condition here. Note that the [action] function is called when this future completes, whether it does so with a value or with an error.

Answer 3

Using an extension on Future and building on Hugo Passos' answer:

extension FutureExtension<T> on Future<T> {
  /// Checks if the future has returned a value, using a Completer.
  bool isCompleted() {
    final completer = Completer<T>();
    then(completer.complete).catchError(completer.completeError);
    return completer.isCompleted;
  }
}