[BUG] ValidationContext is not producing updates.

[BenWhite27]

Describe the bug
ValidationContext does produce updates and current values do not reflect correct validation status or update in response to property changes.
Tested in a UWP project.

Steps To Reproduce
Create a Simple ViewModel and View with associated Bindings.
Create simple validation rules for the ViewModel
Create subscriptions to various Validation public APIs (ValidationContext.ValidationStatusChange, ValidationHelper.ValidationChange, etc.)
Run project and update text in View Controls
Observe that the behavior isn't as expected.

Expected behavior
I'd expect the ValidationContext to produce Observable sequeneces indicating the current status of the ViewModel's validation.

Environment

• OS: Windows 10
• Version 1809+
• Device: Custom build PC and Surface Pro 4

Additional context
I'm seeing updates to ValidationHelper.ValidationChanged in accordance with the associated Validation Rule, but no updates beyond the initial values from ValidationContext.

I've attached a bare bones project I've been using to identify this.
ReactiveUI.Validation.Sample.Uwp.zip

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[BenWhite27]

Some more info.

View Code Behind

this.Bind(this.ViewModel, vm => vm.Username, v => v.userTxt.Text)
    .DisposeWith(disposables);
this.Bind(this.ViewModel, vm => vm.Password, v => v.passTxt.Password)
    .DisposeWith(disposables);
this.BindCommand(this.ViewModel, vm => vm.Login, v => v.loginBtn)
    .DisposeWith(disposables);
this.BindValidation(this.ViewModel, v => v.errorsTxt.Text)
    .DisposeWith(disposables);

ViewModel

public class SampleViewModel : ReactiveObject, ISupportsValidation
{
    private ValidationHelper valHelper1;
    private ValidationHelper valHelper2;

    public SampleViewModel()
    {
        this.Login = ReactiveCommand.Create(() => { Debug.WriteLine("Login Invoked"); }, this.IsValid());
        this.SetupValidations();
    }

    [Reactive] public string Username { get; set; } = "";
    [Reactive] public string Password { get; set; } = "";
    public ReactiveCommand<Unit, Unit> Login { get; }

    public ValidationContext ValidationContext { get; } = new ValidationContext();

    private void SetupValidations()
    {
        this.valHelper1 = this.ValidationRule(vm => vm.Username,
            username => !String.IsNullOrWhiteSpace(username),
            "The username cannot be empty");
        this.valHelper1.ValidationChanged.Subscribe(change =>
        {
            Debug.WriteLine("valHelper1.ValidationChanged");
        });

        this.valHelper2 = this.ValidationRule(vm=>vm.Password,
            password => password?.Length > 6,
            "The password must be longer than 6");
        this.valHelper2.ValidationChanged.Subscribe(change =>
        {
            Debug.WriteLine("valHelper2.ValidationChanged");
        });

        this.ValidationContext.ValidationStatusChange.Subscribe(change =>
        {
            Debug.WriteLine("ValidationContext.ValidationStatusChange");
        });

        this.ValidationContext.Valid.Subscribe(change =>
        {
            Debug.WriteLine("ValidationContext.Valid");
        });

        this.IsValid().Subscribe(valid =>
        {
            Debug.WriteLine("this.IsValid()");
        });
    }
}

So whilst running the above and updating text in the ui controls I'll see debug console output like the following.

// These are the initial values coming from the observables.
valHelper1.ValidationChanged
valHelper2.ValidationChanged
ValidationContext.ValidationStatusChange
ValidationContext.Valid
this.IsValid()

// These are during the test
valHelper1.ValidationChanged
valHelper2.ValidationChanged
valHelper2.ValidationChanged
valHelper1.ValidationChanged
Login Invoked

So whilst the rules are updating just fine the state for the whole object is valid all the time and allows me to execute the command.

[glennawatson]

@alexmartinezm Mind having a look at this one?

[alexmartinezm]

I will check it out over the weekend. Thank you for reporting this @BenWhite27.

[BenWhite27]

Thanks all. I'll download the source myself tonight when I get home and see if I can pin-point it further, I'm still a rookie with Reactive stuff though 😕

Edit - 16:54
More info.
Adding another ValidationRule at a later point via a command suddenly triggers an update from all objects and I can see some validation errors displayed in the UI. The first 2 rules then seem to function properly but the newly added rule doesn't behave correctly, almost as though the text it's producing is 1 property change behind the current value.

[alexmartinezm]

Hi there, I'm trying to fix this bug, but I cannot reproduce this on a XF project and I don't have a Windows machine. However, I have a VM but the debug session is a bit slow. I hope to get this fixed this weekend.

[BenWhite27]

Thanks @alexmartinezm, I had a look at the code but struggled to get my head around it. If there's anything I can do let me know. I could setup a windows VM with Visual Studio and the repro for you to remote desktop into if that helps?

When I was looking at the code I think everything inside BasePropertyValidation.cs was working, but the flow of sequences doesn't seem to get pass this observable.

ReactiveUI.Validation/src/ReactiveUI.Validation/Contexts/ValidationContext.cs

Line 82 in 0b28a7e

_validationConnectable = validationChangedObservable

[worldbeater]

@BenWhite27 for a temporary solution, try passing the ImmediateScheduler.Instance to your ValidationContext constructor. Instead of doing this:

new ValidationContext();

do this:

// The ImmediateScheduler will make your sample work.
new ValidationContext(ImmediateScheduler.Instance);

Currently, _validationSource and _validations won't stay synchronized without the ImmediateScheduler due to the following code blocks:

ReactiveUI.Validation/src/ReactiveUI.Validation/Contexts/ValidationContext.cs

Line 61 in 0b28a7e

.Bind(out _validations)

ReactiveUI.Validation/src/ReactiveUI.Validation/Contexts/ValidationContext.cs

Lines 83 to 88 in 0b28a7e

	.CountChanged()
	.Count()
	.StartWith(0)
	.Select(_ =>
	_validations
	.Select(v => v.ValidationStatusChange)

This issue takes place here due to DynamicData misuse. Feels like I've broken some stuff while migrating from ReactiveList<T> to SourceList<T>. The _validations collection is empty when _validationConnectable ticks on a scheduler other than ImmediateScheduler. Working on a fix now.