CODEWITHSUNDEEP
c#asp.netasp.net-mvcrazor
Daniel Santos
Daniel Santos

Reputation: 15999

ASP.NET MVC Core, How to add a attribute to a input based on the DataType annotation?

How can I add a attribute to a <input /> tag based on the DataType using razor.

For instance if my data does have annotation

[DataType(DataType.Currency)] 
public float Amount {get; set;}

Then I would like to have <input name="Amount" class="currency" > when using the tag helper <input asp-for="Amount " />

Upvotes: 0

Views: 895

Answers (1)

Munir Husseini
Munir Husseini

Reputation: 489

As Stephen Muecke suggested, you'll need to write a TagHelper for this. The TagHelper architecture will provide you with all you need.

using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;

namespace AnnotationBasedAttributes
{
    [HtmlTargetElement("input")]
    public class MyAwesomeTagHelper : TagHelper
    {
        public ModelExpression AspFor { get; set; }

        public override Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
        {
            if (!(this.AspFor.Metadata is DefaultModelMetadata modelMetadata))
            {
                return Task.CompletedTask;
            }

            var dataTypeAttribute = modelMetadata.Attributes.Attributes.OfType<DataTypeAttribute>().FirstOrDefault();
            if (dataTypeAttribute == null)
            {
                return Task.CompletedTask;
            }

            var type = dataTypeAttribute.DataType.ToString().ToLower();
            output.Attributes.Add(new TagHelperAttribute("class", type));

            return Task.CompletedTask;
        }
    }
}

You don't need to do anything special in your view. Just use the input tag helper as usual:

@model IndexModel

<label asp-for="Amount"></label>
<input asp-for="Amount" />

Just don't forget to tell your app to search for TagHelpers in your assembly. Do this in _ViewImports.cshtml:

@addTagHelper *, MyWebApplication

Upvotes: 1

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