ASP.NET Core Model Binding Error Messages Localization in ASP.NET CORE 2.0

Question

In ASP.NET CORE 1.1 it was possible to localize model binding error messages using a resource file and configure its options to set message accessors for ModelBindingMessageProvider in the Startup.cs like

services.AddMvc(options =>
{
    var F = services.BuildServiceProvider().GetService<IStringLocalizerFactory>();
    var L = F.Create("ModelBindingMessages", null);
    options.ModelBindingMessageProvider.ValueIsInvalidAccessor =
        (x) => L["The value '{0}' is invalid."];

as shown here: ASP.NET Core Model Binding Error Messages Localization and here: https://blogs.msdn.microsoft.com/mvpawardprogram/2017/05/09/aspnetcore-mvc-error-message/

In ASP.NET CORE 2.0 I receive an error message on all of the ModelBindingMessageProvider's properties

options.ModelBindingMessageProvider.ValueIsInvalidAccessor 

is readonly

How can these messages be localized in ASP.NET CORE 2.0

Answer 1

In ASP.NET Core 2.0, model binding message provider properties have got read only, but a setter method for each property has been added.

So if you follow the example of my linked post , to set ValueIsInvalidAccessor , you should use SetValueIsInvalidAccessor method this way:

options.ModelBindingMessageProvider.SetValueIsInvalidAccessor (
    (x) => L["The value '{0}' is invalid."]);

Sample Project

I added the sample project for ASP.NET CORE 2.0 in the following repository:

• r-aghaei/AspNetCoreLocalizationSample

Default Error Messages:

• MissingBindRequiredValueAccessor : A value for the '{0}' property was not provided.
• MissingKeyOrValueAccessor : A value is required.
• MissingRequestBodyRequiredValueAccessor : A non-empty request body is required.
• ValueMustNotBeNullAccessor : The value '{0}' is invalid.
• AttemptedValueIsInvalidAccessor : The value '{0}' is not valid for {1}.
• NonPropertyAttemptedValueIsInvalidAccessor : The value '{0}' is not valid.
• UnknownValueIsInvalidAccessor : The supplied value is invalid for {0}.
• NonPropertyUnknownValueIsInvalidAccessor : The supplied value is invalid.
• ValueIsInvalidAccessor : The value '{0}' is invalid.
• ValueMustBeANumberAccessor : The field {0} must be a number.
• NonPropertyValueMustBeANumberAccessor : The field must be a number.

Answer 2

I also ran into this. These setters were replaced with methods such as SetValueIsInvalidAccessor , the change is described here: https://github.com/aspnet/Announcements/issues/240

Answer 3

you could use this configuration for localize mvc core error messages :

public class SomeMvcOptionsSetup : Microsoft.Extensions.Options.IConfigureOptions<Microsoft.AspNetCore.Mvc.MvcOptions>
{
    private readonly Microsoft.Extensions.Localization.IStringLocalizer _resourceLocalizer;

    public SomeMvcOptionsSetup()
    {
    }

    public SomeMvcOptionsSetup(Microsoft.Extensions.Localization.IStringLocalizerFactory stringLocalizerFactory)
    {
        _resourceLocalizer = stringLocalizerFactory.Create(baseName:"ResourceClassName",location:"ResourceNameSpace");
    }

    public void Configure(Microsoft.AspNetCore.Mvc.MvcOptions options)
    {
        options.ModelBindingMessageProvider.SetValueIsInvalidAccessor((x) =>
        {
            if (_resourceLocalizer == null)
            {
                return "Custom Error Message";
            }

            return _resourceLocalizer["Specific Resource Key In Resource File"]; 
        });

        options.ModelBindingMessageProvider.SetValueMustNotBeNullAccessor((x) =>
        {
            if (_resourceLocalizer == null)
            {
                return "Value Can not be null....";
            }
            return _resourceLocalizer["ResourceKeyValueCanNotBeNull"];
        });

  .
  .
  .


    }
}

Then, add the following to your Startup.ConfigureServices(...) method:

 services.TryAddEnumerable(
ServiceDescriptor.Transient<IConfigureOptions<MvcOptions>,SomeMvcOptionsSetup >());

Please see this link