Using a stream viewmodel with stream that requires arguments

[zuboje]

Hello,

I've been using stacked for a while and I love it! I've build a really great application and compared to other framework this one is IMO the best by far. Now I got stack a little bit with a stream and I am not sure how to resolve it. I built viewmodel before StreamViewModel and MultipleStreamViewModel and it works like a charm, now I would like to do something else, I have a stream that is activated upon user input and I have to pass argument to stream before executing it. How would I achieve this in stream view model? I want to map my stream to viewmodel but stream cannot run until user makes a selection on a screen.

[FilledStacks]

Hi @zuboje good question, I can see you've been going deep in Stacked if you have a question like this 😄

To solve this you simply change the Stream in the ViewModel, then rebuild it.

So we have a function called notifySourceChanged that can be called when a source has changed. What this will allow you to do is start change the stream to a new stream with the same data type dynamically.

So in your case, you would start the ViewModel with an Empty Stream, that does nothing.

When you have the data you need to create the Stream you want, you can set that to the source, and then call notifySourceChanged. Here's a small example, I'll comment on it.

  late Stream<int> _currentSource; // <== The stream we'll use to change sources

  StreamCounterViewModel() {
    _setSource();
  }

  void _setSource() {
    _currentSource = isSlowEpochNumbers // <==== Change the source to what we want it to be
        ? exampleLocator<EpochService>().epochUpdatesNumbers()
        : exampleLocator<EpochService>().epochUpdateNumbersQuickly();
  }

  @override
  Stream<int> get stream => _currentSource; <== Instead of using the Stream directly, use the variable

  void changeStreamSources() {
    isSlowEpochNumbers = !isSlowEpochNumbers;
    _setSource();
    notifySourceChanged(); // <== After source has been changed we notify Stacked about it
  }

Stacked will manage the stream for you by unsubscribing, disposing, then resubscribing and running everything as usual with the new Stream.

Goodluck 🤜

[FilledStacks]

You can see this in the Stacked example under stream_counter_viewmodel.dart

[zuboje]

Thnk you @FilledStacks! This indeed solves my problem, you guys are awesome, keep it going!