To customize framework model binding error messages, you need to set custom accessors for different error message accessors of ModelBindingMessageProvider
.
Example
Here you can download a full source code of what is described in this post. The repository contains example for ASP.NET Core 2.0 (VS 2017.3) and ASP.NET Core 1.1 (VS 2015):
- r-aghaei/AspNetCoreLocalizationSample
Also here you can see the example, live:
- aspnetcorelocalizationsample.azurewebsites.net
Default Error Messages
These are default error messages which the framework shows when model binding to a property fails:
MissingBindRequiredValueAccessor A value for the '{0}' property was not provided.
MissingKeyOrValueAccessor A value is required.
ValueMustNotBeNullAccessor The value '{0}' is invalid.
AttemptedValueIsInvalidAccessor The value '{0}' is not valid for {1}.
UnknownValueIsInvalidAccessor The supplied value is invalid for {0}.
ValueIsInvalidAccessor The value '{0}' is invalid.
ValueMustBeANumberAccessor The field {0} must be a number.
In addition to above messages, ASP.NET Core 2.0 have these messages as well:
MissingRequestBodyRequiredValueAccessor A non-empty request body is required.
NonPropertyAttemptedValueIsInvalidAccessor The value '{0}' is not valid.
NonPropertyUnknownValueIsInvalidAccessor The supplied value is invalid.
NonPropertyValueMustBeANumberAccessor The field must be a number.
Localize ASP.NET Core Model Binding Error Messages
To localize ASP.NET Core model binding error messages, follow these steps:
-
Create Resource File – Create a resource file under Resources folder in your solution and name the file ModelBindingMessages.fa.resx. The name can be anything else but we will use it to create a localizer. In the example, I used fa (Persian) culture.
-
Add Resource Keys – Open the resource file and add keys and values which you want to use for localizing error messages. I used keys and values like below image:
Keys which I used are like original messages, except the key for
ValueMustNotBeNull
which was the same asValueIsInvalid
, so I used Null value is invalid. for it. -
Configure Options – In
ConfigureServices
method, when addingMvc
, configure its options to set message accessors forModelBindingMessageProvider
:public void ConfigureServices(IServiceCollection services) { services.AddLocalization(options => { options.ResourcesPath = "Resources"; }); services.AddMvc(options => { var F = services.BuildServiceProvider().GetService<IStringLocalizerFactory>(); var L = F.Create("ModelBindingMessages", "AspNetCoreLocalizationSample"); options.ModelBindingMessageProvider.ValueIsInvalidAccessor = (x) => L["The value '{0}' is invalid.", x]; options.ModelBindingMessageProvider.ValueMustBeANumberAccessor = (x) => L["The field {0} must be a number.", x]; options.ModelBindingMessageProvider.MissingBindRequiredValueAccessor = (x) => L["A value for the '{0}' property was not provided.", x]; options.ModelBindingMessageProvider.AttemptedValueIsInvalidAccessor = (x, y) => L["The value '{0}' is not valid for {1}.", x, y]; options.ModelBindingMessageProvider.MissingKeyOrValueAccessor = () => L["A value is required."]; options.ModelBindingMessageProvider.UnknownValueIsInvalidAccessor = (x) => L["The supplied value is invalid for {0}.", x]; options.ModelBindingMessageProvider.ValueMustNotBeNullAccessor = (x) => L["Null value is invalid.", x]; }) .AddDataAnnotationsLocalization() .AddViewLocalization(); services.Configure<RequestLocalizationOptions>(options => { var supportedCultures = new[]{new CultureInfo("en"), new CultureInfo("fa")}; options.DefaultRequestCulture = new RequestCulture("en", "en"); options.SupportedCultures = supportedCultures; options.SupportedUICultures = supportedCultures; }); }
Also add this code at beginning of
Configure
method:var supportedCultures = new[] { new CultureInfo("en"), new CultureInfo("fa") }; app.UseRequestLocalization(new RequestLocalizationOptions() { DefaultRequestCulture = new RequestCulture(new CultureInfo("en")), SupportedCultures = supportedCultures, SupportedUICultures = supportedCultures });
Important Note for ASP.NET Core 2.0
In ASP.NET Core 2.0, model binding message provider properties has got
read only, but a setter method for each property has been added.For example, to set
ValueIsInvalidAccessor
, you should useSetValueIsInvalidAccessor()
method this way:options.ModelBindingMessageProvider.SetValueIsInvalidAccessor ( (x) => L["The value '{0}' is invalid.", x]);