Custom Attribute in c# to give Custom data-attribute in html

Question

I'd like to be able to make a data attribute in c# for an object in my model. When this is displayed. I'd like the html to render the value in a data attribute within the html itself.

In my head, the code looks similar to this.

public class AffectsAttribute:Attribute
{
    public string[] Departments { get; set; }

}


[EmailAddress]
[Required(ErrorMessage = "Email is required")]
[Affects(Departments = new string[]{"Coaches"})]
public string Email {get; set;}

Then in the html, after being called with razor it would look something like this

@Html.EditorFor(model => model.Email)


<input class="text-box single-line" data-affects="Coaches" data-val="true" data-val-email="The Email field is not a valid e-mail address." data-val-required="Email is required" id="Email" name="Email" type="email"  value="">

I have no clue how to specify that I would like the additional data attribute to be added when the item is rendered on a page. Can anyone help?

here is the answer: http://stackoverflow.com/questions/2493143/how-do-you-read-the-value-of-an-attribute-in-a-method — Legends, Apr 29 '15 at 13:42
@Legends I'd do that so that the developer working on the business layer can point out dependencies between areas, then we can warn users when they update. — LiamHT, Apr 29 '15 at 13:48
Why not use [AdditionalMetadata](https://msdn.microsoft.com/en-us/library/system.web.mvc.additionalmetadataattribute(v=vs.118).aspx)? — Andrei V, Apr 29 '15 at 13:49
Because the Business layer, Therefore the models are not in an MVC project. We have seperated the two entirely. — LiamHT, Apr 29 '15 at 13:51
@Legends also, your answer shows me how to access them within c#. Do I have to have a custom class to tell razor how to write the html? — LiamHT, Apr 29 '15 at 13:52
You don't need a custom class but you do need custom logic. You need to get the data stored by the attribute in order to *save it* in your HTML. — Andrei V, Apr 29 '15 at 13:57
my only problem is that any model data requires me to use the MVC namespace. as my model is situated in a business layer (class library) i do not have that information presently. So even using additionalMetadata as Andrei said doesnt work... Any ideas for a work around? — LiamHT, Apr 29 '15 at 15:10
Html helpers generate attributes based on the metadata of the property. Your attribute would need to implement `IMetadataAware` and you would need to create a custom html helper ([example here](http://stackoverflow.com/questions/26519493/customattribute-reflects-html-attribute-mvc5/26519946#26519946)). In any case claiming your model is in a business layer is irrelevant. You should always be using a view model for editing data. — , Apr 30 '15 at 00:00

score 1 · Answer 1 · answered Apr 29 '15 at 13:56

It can be done through the ValidationAttribute. If you inherit this:

public class MyCustomAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
    }
}

The GetClientValidationRules is what you are interested in. You return an IEnumerable of attributes you want the client to have.

You can check out this article on CodeProject.

my only problem is that any model data requires me to use the MVC namespace. as my model is situated in a business layer (class library) i do not have that information presently — LiamHT, Apr 29 '15 at 14:52

score 0 · Answer 2 · answered Apr 29 '15 at 13:57

You'll have to create a new HTML helper to do that. http://www.asp.net/mvc/overview/older-versions-1/views/creating-custom-html-helpers-cs

It's an extension from the HtmlHelper, that creates that. Something like:

  public static class YourExtensions
 {
      public static string YourMethodName(this HtmlHelper helper, string[] paramName)
      {
           return  String.Format("<input data-affects='{0}'>",String.Join(" ", paramName));
      }
 }

Custom Attribute in c# to give Custom data-attribute in html

2 Answers2