[Question] Initial List Validation / Getting IsValid

[mysteryx93]

I'm trying to do something very simple. I want to validate that the Sources ObservableCollection is not empty.

var sourceNotEmpty = Sources
    .ToObservableChangeSet(x => x.Path)
    .ToCollection()
    .Select(x => x.Any());
this.ValidationRule(x => x.Sources,
    sourceNotEmpty,
    "You must select source files or folders to encode");

Testing GetErrors works except for this test. It fails because the ValidationRule hasn't yet been evaluated. If I add an item and then remove it, then it works.

[Fact]
public void GetErrors_SourceEmpty_Error()
{
    var errors = Model.GetErrors(nameof(Model.Sources));

    Assert.Single(errors);  // errors is empty
}

Then, how do I get IsValid? Before doing some work in the ViewModel, I first need to check "IsValid" but haven't yet found the way to get the current value. LastAsync won't work if it hasn't yet been evaluated.

[Fact]
public void IsValid_MissingData_ReturnsFalse()
{
    bool? result = null;

    Model.IsValid().Do(x => result = x);
    
    Assert.False(result);
}

These 2 things are extremely simple but there's probably something I'm missing with the whole paradigm?

Adding to this, on the UI, I probably don't want to display all the "field missing" errors right away, but only when he tries to click Submit or re-empties a field after typing in it.

[mysteryx93]

Alright I've made progress on this after spending the day reading through the docs. Can you tell me whether I'm doing it right?

To get initial list validation, calling Sources.Clear() works.

var sourceNotEmpty = Sources
    .ToObservableChangeSet(x => x.Path)
    .ToCollection()
    .Select(x => x.Any());
this.ValidationRule(x => x.Sources,
    sourceNotEmpty,
    "You must select source files or folders to encode");
this.Sources.Clear();

To get IsValid...

constructor...
    _isValid = this.IsValid().ToProperty(this, x => x.IsValidValue);
}

readonly ObservableAsPropertyHelper<bool> _isValid;
public bool IsValidValue
{
    get { return _isValid.Value; }  
}	

Is this the right way? I would think that this should instead be in the base ReactiveValidationObject.