问题
Why can't I do like this?
[Required(ErrorMessage = "*")]
[RegularExpression("^[a-zA-Z0-9_]*$", ErrorMessage = Resources.RegistrationModel.UsernameError)]
public string Username { get; set; }
What is the error message telling me?
An attribute argument must be a constant expression , typeof expression or array creation expression of an attribute parameter type.
回答1:
When you are using the ErrorMessage
property only constant strings or string literal can be assigned to it.
Use the ErrorMessageResourceType
and ErrorMessageResourceName
instead to specity your resources.
[RegularExpression(
"^[a-zA-Z0-9_]*$",
ErrorMessageResourceType=typeof(Resources.RegistrationModel),
ErrorMessageResourceName= "UsernameError"
)]
Note that the resources must be public (can be set in the resource editor).
回答2:
Please see this link: http://code.msdn.microsoft.com/Getting-Started-WCF-RIA-1469cbe2/sourcecode?fileId=19242&pathId=774666288 (link broken, but left for attribution purposes)
public sealed partial class RegistrationData
{
[Key]
[Required(ErrorMessageResourceName = "ValidationErrorRequiredField", ErrorMessageResourceType = typeof(ErrorResources))]
[Display(Order = 0, Name = "UserNameLabel", ResourceType = typeof(RegistrationDataResources))]
[RegularExpression("^[a-zA-Z0-9_]*$", ErrorMessageResourceName = "ValidationErrorInvalidUserName", ErrorMessageResourceType = typeof(ErrorResources))]
[StringLength(255, MinimumLength = 4, ErrorMessageResourceName = "ValidationErrorBadUserNameLength", ErrorMessageResourceType = typeof(ErrorResources))]
public string UserName { get; set; }
回答3:
Try FluentModelMetaDataProvider.
Managed to use resources for error messages in strongly typed fashion.
Looks like this:
using System.Web.Mvc.Extensibility;
namespace UI.Model
{
public class StoreInputMetadata : ModelMetadataConfigurationBase<StoreInput>
{
public StoreInputMetadata()
{
Configure(m => m.Id)
.Hide();
Configure(model => model.Name)
.Required(Resources.Whatever.StoreIsRequired)
.MaximumLength(64, Resources.Whatever.StoreNameLengthSomething);
}
}
}
What is the error message telling me?
An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type.
It's already self explanatory. C# isn't dynamic language like Ruby where You can write classes that inherits random base class at runtime. :)
Here's what Skeet says about this.
回答4:
It means that you cannot determine the value of the argument you are passing into the attribute at runtime
, it must be at compile time
so the value is embedded into the assembly.
The error message value needs to be a constant expression.
For information, attribute arguments can only be of types bool, byte, char, short, int, long, float, double, string, System.Type, and enums.
回答5:
You should instead look at the ErrorMessageResourceName
and ErrorMessageResourceType
properties of this attribute. They do allow the error message to be pulled from a resource.
来源:https://stackoverflow.com/questions/2688888/why-cant-i-use-resources-as-errormessage-with-dataannotations