C# – ASP.NET MVC4: An attribute argument must be a constant expression , typeof expression or array creation expression of an attribute parameter type

asp.net-mvcasp.net-mvc-4cdata-annotations

I had the following code:

    [Required(ErrorMessage = MessageModel.translateMessage("required")))]
    [Display(Name= MessageModel.translateMessage("id"))]
    public string user_id { get; set; }

I am trying to make the error message dynamic but I get error when compiled.:

"An attribute argument must be a constant expression , typeof expression or array creation expression of an attribute parameter type."

Any solution for this issue?

Best Answer

First you create a Resource .resx file this will contain your localised strings.

When you declare the attribute you set the ResourceType argument. This causes the Name, ShortName and Description arguments to be used as a resource key instead of a value.

[Display(Name = "GenreName", ShortName = "GenreShortName", Description = "GenreDescription", ResourceType = typeof(MyResources))]
public string Genre { get; set; }

Related Solutions

C# – DisplayName attribute from Resources

If you use MVC 3 and .NET 4, you can use the new Display attribute in the System.ComponentModel.DataAnnotations namespace. This attribute replaces the DisplayName attribute and provides much more functionality, including localization support.

In your case, you would use it like this:

public class MyModel
{
    [Required]
    [Display(Name = "labelForName", ResourceType = typeof(Resources.Resources))]
    public string name{ get; set; }
}

As a side note, this attribute will not work with resources inside App_GlobalResources or App_LocalResources. This has to do with the custom tool (GlobalResourceProxyGenerator) these resources use. Instead make sure your resource file is set to 'Embedded resource' and use the 'ResXFileCodeGenerator' custom tool.

(As a further side note, you shouldn't be using App_GlobalResources or App_LocalResources with MVC. You can read more about why this is the case here)

C# – Attribute error: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

Please pardon me if my C# coding is off. I use VB.

You can use const values.

namespace Enums {
    static class SecurityRight {
        const String A = "A";
        const String B = "B";
    }
}

[MyAtt(StringProperty = Enums.SecurityRight.A + "&" + Enums.SecurityRight.B)]

You can use an enum if the attribute accepts the same data type as an enum.

namespace Enums {
    [Flags()]
    enum int SecurityRight {
        A = 1;
        B = 2;
    }
}

[MyAtt(IntegerProperty = Enums.SecurityRight.A | Enums.SecurityRight.B)]

EDIT: Changed IntegerProperty above to receive multiple values.

Attributes are set at compile time, not at runtime. By using ToString, you are invoking code that is used in runtime. You must use a constant value.

Best Answer

Related Solutions

C# – DisplayName attribute from Resources

C# – Attribute error: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type

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