Feature Request: An `IsResolved` property/method to be included to check if a node has had it's dependencies resolved

[Soren025]

One thing I find my self doing is the following structure.

[Meta(typeof(IDependent))]
public partial class Foo: Node
{
    [Dependency]
    public Bar Bar => this.DependOn<Bar>();
    
    private bool IsResolved { get; set; }
    
    public override void _Notification(int what)
    {
        this.Notify(what);
    }

    public void OnResolved()
    {
        Bar.SomeEvent += OnSomeEvent;
        IsResolved = true;
    }

    public override void _ExitTree()
    {
        if (IsResolved)
        {
            Bar.SomeEvent -= OnSomeEvent;
        }
    }

    private void OnSomeEvent() { }
}

Foo wants to unregister events from a dependency when it's removed from it's parent, but if it's removed before OnResolved() is called it might result in errors due to an unresolved dependency. So I have found the need to add a bool property to check if OnResolved() has been called.

[blewis-web]

Just wanted to mention that I also do this all the time.

[wlsnmrk]

We'd need to figure out, if AutoInject were to manage such a property, under what circumstances it should be reset to false. E.g., if a node will enter and exit the tree many times, and will be provided a new dependency value each time, the IsResolved property should presumably be set to false at some point during the tree exit -- but in the example given, not before the user's _ExitTree() is called.

[blewis-web]

For my own use case, I most often have IsResolved guard clauses in event handlers, public methods (usually not related to Node lifecycle), and any side effects in properties. I just checked and I don't have any IsResolved guard clauses on _ExitTree or OnExitTree in particular, but I see one in _Process. I do have one instance where we have an is not null guard clause that does something similar in _ExitTree just to be safe.

I can see a benefit to AutoInject handling that via a public bool IsResolved { get; private set; } property, keeping it up to date - and letting users opt-in to using it as they see fit. Sounds like that might be hard to get right, but it might simplify things a bit for the average user.