Reactions to nested Atoms

[slimshader]

Hi,

I think I am missing something still, code sample:

public class ExperimentsWindow : Window
{
    class ViewModel
    {
        [Atom]
        public int IntValue { get; set; } 
    }

    [Atom]
    ViewModel VM { get; set; }

    private void Start()
    {
        Initialize();

        VM = new ViewModel() { IntValue = 5 };

        // tried this too: Atom.Reaction(() => Debug.Log($"Int value {VM.IntValue}"));
        Atom.Reaction(() => VM.IntValue, i => Debug.Log($"Int value {i}"));

        VM.IntValue = 6;

        VM = new ViewModel() { IntValue = 7 };
    }
}

When running, I always only see values "5" or "7" printed but not "6". Is there a way to React to changes in multi-level Atoms?

[vanifatovvlad]

The reactions are executed in two cases:

1. on creation;
2. on the next frame after any dependant atom changed.

In this sample, a value "5" is printed immediately when creating a reaction. Values "6" and "7" are set during one frame. They trigger a reaction, but the reaction itself is executed once on the next frame and use latest values (so "7" is printed).

The value "6" will be printed if the values are set in different frames, or if you force actualize a reaction.

private IEnumerator Start()
{
    VM = new ViewModel() {IntValue = 5};

    Atom.Reaction(() => Debug.Log($"Int value {VM.IntValue}"));

    VM.IntValue = 6;
    yield return null; // skip one frame

    VM = new ViewModel() {IntValue = 7};
}

private void Start()
{
    VM = new ViewModel() {IntValue = 5};

    var reaction = Atom.Reaction(() => Debug.Log($"Int value {VM.IntValue}"));

    VM.IntValue = 6;
    reaction.Activate(); // force actualize

    VM = new ViewModel() {IntValue = 7};
}

[slimshader]

Ah, makes perfect sense now. The fact that Reaction is only triggered next frame with latest value could be leveraged as optimization I suppose then, no need to discard intermediate updates to the values as they will not force UI update anyways.

Question: could you clarify the difference between Reaction(Action reaction) and Reaction(AtomPull react, Action effect)? When to use which one?

[vanifatovvlad]

Reaction(AtomPull react, Action effect) tracks atoms that used in react method, and won't track atoms in effect method.

For example, this reaction:

Atom.Reaction(() => {
   var val = myAtom;
   otherPlugin.Process(val);
});

will executed when myAtom value changed, but potentially otherPlugin can access other atoms in Process method, so reaction will track them too.

If you dont want this behaviour, you can use Reaction(AtomPull react, Action effect) overload to control which data should be tracked.

In this sample reaction wont track atoms used in Process method.

Atom.Reaction(
   () => myAtom,
   val => otherPlugin.Process(val)
);

Or you can use NoWatch

Atom.Reaction(() => {
   var val = myAtom;
   using (Atom.NoWatch) {
      otherPlugin.Process(val);
  }
});