How to translate the "ErrorMessage" from a "Custom Attribute"

Question

I created a Custom Validation Attribute that only validates if a CPF property is a valid CPF, but when I Localize the application I noticed that my Custom Attribute was not having its messages localized by the Framework, unlike the Data Attribute Required that has its message located correctly:

Example of using attributes with Required being correctly localized.

[Required(ErrorMessage = "CPF Requerido")]
[CPF(ErrorMessage = "CPF Inválido")]
public string CPF { get; set; }

Setting the location in the Startup.cs file

services
    .AddMvc()
    .SetCompatibilityVersion(CompatibilityVersion.Version_2_1)
    .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
    .AddDataAnnotationsLocalization(options =>
    {
        options.DataAnnotationLocalizerProvider = (type, factory) =>
        {
             return factory.Create(typeof(SharedResource));
        };
    });

Custom validation class:

public class CPFAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext context)
    {
        //Omitted for not being part of the context
    }
}

Versions:

Microsoft.AspNetCore.App (2.1.1)

Microsoft.NETCore.App (2.1)

Possible duplicate of [ASP.NET Core custom validation attribute localization](https://stackoverflow.com/questions/42784311/asp-net-core-custom-validation-attribute-localization) — jpgrassi, Apr 07 '19 at 09:13

score 5 · Accepted Answer · edited Jul 21 '19 at 13:01

Implement the Attripute Adapter:

public class CPFAttributeAdapter : AttributeAdapterBase<CPFAttribute>
{
        public CPFAttributeAdapter(CPFAttributeattribute, IStringLocalizer stringLocalizer) : base(attribute, stringLocalizer) { }

    public override void AddValidation(ClientModelValidationContext context) { }
        public override string GetErrorMessage(ModelValidationContextBase validationContext)
        {
            return GetErrorMessage(validationContext.ModelMetadata, validationContext.ModelMetadata.GetDisplayName());
        }
    }

And implement the Attripute Adapter Provider:

public class CPFAttributeAdapterProvider : IValidationAttributeAdapterProvider
{
    private readonly IValidationAttributeAdapterProvider _baseProvider = new ValidationAttributeAdapterProvider();

    public IAttributeAdapter GetAttributeAdapter(CPFAttribute attribute, IStringLocalizer stringLocalizer)
    {
        if (attribute is CPFAttribute)
            return new CPFAttributeAdapter(attribute as CPFAttribute, stringLocalizer);
        else
            return _baseProvider.GetAttributeAdapter(attribute, stringLocalizer);
    }

    public IAttributeAdapter GetAttributeAdapter(ValidationAttribute attribute, IStringLocalizer stringLocalizer)
    {
        if (attribute is CPFAttribute) return
                new CPFAttributeAdapter(attribute as CPFAttribute,
        stringLocalizer);
        else return _baseProvider.GetAttributeAdapter(attribute, stringLocalizer);
    }
}

And write this in Startup.cs:

    services.AddSingleton<IValidationAttributeAdapterProvider, CPFAttributeAdapterProvider>();

How to translate the "ErrorMessage" from a "Custom Attribute"

1 Answers1