BlazorEditForms/FluentValidationFormComponent.cs

using FluentValidation;
using FluentValidation.Internal;

using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Forms;

namespace BlazorEditForms;

public class FluentValidationFormComponent : ComponentBase
{
    [CascadingParameter] EditContext? CurrentEditContext { get; set; }

    [Parameter] public IValidator? Validator { get; set; }

    [Inject] private IServiceProvider ServiceProvider { get; set; } = default!;

    private ValidationMessageStore? _messages;

    protected override void OnInitialized()
    {
        if (CurrentEditContext == null)
        {
            throw new InvalidOperationException($"{nameof(FluentValidationFormComponent)} requires a cascading parameter of type {nameof(EditContext)}");
        }

        if (Validator == null)
        {
            throw new InvalidOperationException($"{nameof(FluentValidationFormComponent)} requires a parameter of type {nameof(IValidator)}");
        }

        _messages = new ValidationMessageStore(CurrentEditContext);
        CurrentEditContext.OnFieldChanged += CurrentEditContext_OnFieldChanged;
        CurrentEditContext.OnValidationRequested += CurrentEditContext_OnValidationRequested;
    }


    private async void CurrentEditContext_OnFieldChanged(object? sender, FieldChangedEventArgs e)
    {
        //var context = new ValidationContext<object>(e.FieldIdentifier.Model, new PropertyChain(), new MemberNameValidatorSelector([e.FieldIdentifier.FieldName]));
        var context = new ValidationContext<object>(CurrentEditContext!.Model, new PropertyChain(), new MemberNameValidatorSelector([e.FieldIdentifier.FieldName]));
        var validationResults = await Validator!.ValidateAsync(context);

        _messages!.Clear(e.FieldIdentifier);
        foreach (var validationResult in validationResults.Errors)
        {
            _messages.Add(e.FieldIdentifier, validationResult.ErrorMessage);
        }

        CurrentEditContext!.NotifyValidationStateChanged();
    }

    private async void CurrentEditContext_OnValidationRequested(object? sender, ValidationRequestedEventArgs e)
    {
        var context = new ValidationContext<object>(CurrentEditContext!.Model);
        var validationResults = await Validator!.ValidateAsync(context);

        _messages!.Clear();
        foreach (var validationResult in validationResults.Errors)
        {
            var fieldIdentifier = CurrentEditContext.Field(validationResult.PropertyName);
            _messages.Add(fieldIdentifier, validationResult.ErrorMessage);
        }

        CurrentEditContext.NotifyValidationStateChanged();
    }
}