feature: Improved IDisposable Handling, Possibility to Change Validation Rules Dynamically

[worldbeater]

What kind of change does this PR introduce?

This PR allows IValidationComponents to be detached from a ValidationContext.

What is the current behavior?

As described in #71, currently there is no way to detach an IValidationComponent if it is attached to a ValidationContext. Although it is possible to write WhenAnyValue-based ValidationRules that respect the observable and mutable state of a validated view model, sometimes it may be easier to just remove and dispose of a specific IValidationComponent.

Currently there is no way to dispose of a BasePropertyValidation and of a ModelObservableValidation, see https://github.com/reactiveui/ReactiveUI.Validation/blob/main/src/ReactiveUI.Validation/Extensions/ValidatableViewModelExtensions.cs#L58 If we call the ValidationRule() extension method, a new instance of a disposable IValidationComponent is created and attached to the ValidationContext. Notably, the disposable validation component is never disposed of. Also, currently, there is no way to dispose of the validation component manually, the IValidationComponent interface doesn't implement IDisposable, and the ValidationHelper doesn't dispose of the underlying IValidationComponent.

What is the new behavior?

Now, if we dispose of the ValidationHelper that is returned by a call to ValidationRule, it will dispose of an underlying BasePropertyValidation or a ModelObservableValidation automatically. Also, it will detach the IValidationComponent from the ValidationContext before disposal. Also, it is now possible to detach any validation components manually from the validation context. We are now accessing the ReadOnlyObservableCollection<IValidationComponent> in a reactive fashion both in our INotifyDataErrorInfo implementation, and in the BindValidation extension method. This allows putting ValidationRules into a WhenActivated block e.g.

this.WhenActivated(disposables =>
{
    this.ValidationRule(
        x => x.UserName,
        name => !string.IsNullOrWhiteSpace(name),
        "UserName shouldn't be null or white space.")
        .DisposeWith(_compositeDisposable);
});

What might this PR break?

Hopefully nothing.

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

[codecov]

Codecov Report

Merging #115 into main will increase coverage by 1.51%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   52.73%   54.25%   +1.51%     
==========================================
  Files          16       16              
  Lines         895      894       -1     
==========================================
+ Hits          472      485      +13     
+ Misses        423      409      -14     

Impacted Files	Coverage Δ
ValidationBindings/ValidationBinding.cs	79.36% <0.00%> (-3.07%)	⬇️
Extensions/ValidatableViewModelExtensions.cs	52.74% <0.00%> (-1.80%)	⬇️
Helpers/ReactiveValidationObject.cs	97.29% <0.00%> (+0.32%)	⬆️
Contexts/ValidationContext.cs	91.66% <0.00%> (+1.19%)	⬆️
Components/ModelObservableValidationBase.cs	90.00% <0.00%> (+10.00%)	⬆️
Extensions/ValidationContextExtensions.cs	27.45% <0.00%> (+10.30%)	⬆️
Components/BasePropertyValidation.cs	92.85% <0.00%> (+10.71%)	⬆️
Helpers/ValidationHelper.cs	100.00% <0.00%> (+28.57%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f0040f9...7f2a2ba. Read the comment docs.