Event and EventHandle in Dart

I'm coming from C# and I understand (more or less) the logic around the Events and how they works. Now, I have to traduce an event paradigm (with data passing) from C# to Dart but I don't understand how it works on Dart. Can anyone explain to me patiently? Thanks

EDIT: These are the pieces of code that i have to translate

Class Engine.cs

public class Engine {
    [...]
    public event EventHandler<EngineComputationEventArgs> ComputationCompleted;

     protected virtual void OnComputationCompleted(Result result) {
         var evt = ComputationCompleted;
         if (evt != null) {
             evt(this, new EngineComputationEventArgs(result));
         }
     }
}

Class Example.cs

[...]

engine.ComputationCompleted += (sender, e) => {
    Console.WriteLine("PPE {0}", e.Result.Ppe);
};

[...]

and EngineComputationEventArgs.cs

public class EngineComputationEventArgs : EventArgs {

    public EngineComputationEventArgs(Result result) {
        Result = result;
    }

    public Result Result { get; private set; }

}

Dart does not have built in "Event" types like C# does. You usually use a Stream as event emitter, and a corresponding StreamController to add events to it.

Example:

class Engine {
  final StreamController<EngineComputationEventArgs> _computationCompleted =
     StreamController.broadcast(/*sync: true*/);

  Stream<EngineComputationEventArgs> get computationCompleted => 
      _computationCompleted.stream;

  void onComputationCompleted(Result result) {
    if (_computationCompleted.hasListener) {
      _computationCompleted.add(EngineComputationEventArgs(result));
    }
  }
}

You then add listeners by listening on the stream:

engine.computationCompleted.forEach((e) =>
    print("PPE ${e.result.ppe}"));

or

var subscription = engine.computationCompleted.listen((e) =>
    print("PPE ${e.result.ppe}"));
// Can call `subscription.cancel()` later to stop listening.

Your "args" class could be (since I know nothing about EventArgs)

class EngineComputationEventArgs extends EventArgs {
  final Result result;
 
  EngineComputationEventArgs(this.result);
}