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How can I modify LabelFor to display an asterisk on required fields?

Posted by: admin November 29, 2017 Leave a comment

Questions:

I want to create an extension method for HtmlHelper that allows me to create a LabelFor a property display an asterisk after it if it is a required field. How can I do that?

public class Foo
{
    [Required]
    public string Name { get; set; }
}

Html.LabelFor(o => o.Name) // Name*
Answers:

Here is an blog post that describes how to do this.

To give you a small example modified from the site above (note – I have not compiled/tested this):

namespace HelpRequest.Controllers.Helpers
{
   public static class LabelExtensions
    {
        public static MvcHtmlString Label(this HtmlHelper html, string expression, string id = "", bool generatedId = false)
        {
            return LabelHelper(html, ModelMetadata.FromStringExpression(expression, html.ViewData), expression, id, generatedId);
        }

        [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
        public static MvcHtmlString LabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, string id = "", bool generatedId = false)
        {
            return LabelHelper(html, ModelMetadata.FromLambdaExpression(expression, html.ViewData), ExpressionHelper.GetExpressionText(expression), id, generatedId);
        }

        internal static MvcHtmlString LabelHelper(HtmlHelper html, ModelMetadata metadata, string htmlFieldName, string id, bool generatedId)
        {
            string labelText = metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();
            if (String.IsNullOrEmpty(labelText))
            {
                return MvcHtmlString.Empty;
            }
            var sb = new StringBuilder();
            sb.Append(labelText);
            if (metadata.IsRequired)
                sb.Append("*");

            var tag = new TagBuilder("label");
            if (!string.IsNullOrWhiteSpace(id))
            {
                tag.Attributes.Add("id", id);
            }
            else if (generatedId)
            {
                tag.Attributes.Add("id", html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName) + "_Label");
            }

            tag.Attributes.Add("for", html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName));
            tag.SetInnerText(sb.ToString());

            return MvcHtmlString.Create(tag.ToString(TagRenderMode.Normal));
        }
    }
}

Questions:
Answers:

You can add an asterisk to a required field purely through CSS.

First, create a CSS class for it:

.required:after 
{
    content: "*";
    font-weight: bold;
    color: red; 
}

This will append a red asterisk to any element with the “required” class.

Then, in your view, simply add the new class to your label:

    @Html.LabelFor(m => m.Name, new { @class="required" })

Even better might be a custom HTML Helper that discerns if the field has a [Required] attribute, and if so, adds the “required” CSS class.

Questions:
Answers:

I did that way because my required fields must be dynamic (defined in a configuration file)

Add at the end of your View:

    <script type="text/javascript">
        $('input[type=text]').each(function () {
            var req = $(this).attr('data-val-required');
            if (undefined != req) {
                var label = $('label[for="' + $(this).attr('id') + '"]');
                var text = label.text();
                if (text.length > 0) {
                    label.append('<span style="color:red"> *</span>');
                }
            }
        });
    </script>

Questions:
Answers:

Here is my solution based on Adam Tuliper’s answer but modified to work with Bootstrap and also allow the usage of custom attributes.

using System;
using System.Linq;
using System.Web.Mvc;
using System.Linq.Expressions;
using System.ComponentModel;


public static class RequiredLabel
{
    public static MvcHtmlString RequiredLabelFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, object htmlAttributes)
    {
        var metaData = ModelMetadata.FromLambdaExpression(expression, helper.ViewData);

        string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
        string labelText = metaData.DisplayName ?? metaData.PropertyName ?? htmlFieldName.Split('.').Last();

        if (metaData.IsRequired)
            labelText += "<span class=\"required\">*</span>";

        if (String.IsNullOrEmpty(labelText))
            return MvcHtmlString.Empty;

        var label = new TagBuilder("label");
        label.Attributes.Add("for", helper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName));

        foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(htmlAttributes))
        {
            label.MergeAttribute(prop.Name.Replace('_', '-'), prop.GetValue(htmlAttributes).ToString(), true);
        }

        label.InnerHtml = labelText;
        return MvcHtmlString.Create(label.ToString());
    }

}

Then, I call it from my view like this:

@Html.RequiredLabelFor(model => model.Category, new { @class = "control-label col-md-3" })

P.S. Make sure you don’t forget to include your namespace in your view.

Questions:
Answers:

see this post here – should contain most of what you need
http://blogs.planetcloud.co.uk/mygreatdiscovery/post/Creating-tooltips-using-data-annotations-in-ASPNET-MVC.aspx

public static MvcHtmlString RequiredLabelFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression)
{
    var metaData = ModelMetadata.FromLambdaExpression(expression, helper.ViewData);

    string htmlFieldName = ExpressionHelper.GetExpressionText(expression);
    string labelText = metaData.DisplayName ?? metaData.PropertyName ?? htmlFieldName.Split('.').Last();

    if (metaData.IsRequired)
        labelText += "<span class=\"required-field\">*</span>";

    if (String.IsNullOrEmpty(labelText))
        return MvcHtmlString.Empty;

    var label = new TagBuilder("label");
    label.Attributes.Add("for", helper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldId(htmlFieldName));

    label.InnerHtml = labelText;
    return MvcHtmlString.Create(label.ToString());
}

Questions:
Answers:

Use helper to add style class to the label

public static MvcHtmlString RequiredLabelFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, object htmlAttributes)
{
    var metadata = ModelMetadata.FromLambdaExpression(expression, html.ViewData);
    var resolvedLabelText = metadata.DisplayName ?? metadata.PropertyName;
    if (!metadata.IsRequired)
    {
        return html.LabelFor(expression, resolvedLabelText, htmlAttributes);
    }

    var attributes = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);
    if (attributes == null)
    {
        return html.LabelFor(expression, resolvedLabelText, htmlAttributes);
    }

    const string requiredClass = "required-label";
    if (attributes.ContainsKey("class"))
    {
        var classList = attributes["class"].ToString().Split(' ').ToList();
        classList.Add(requiredClass);
        attributes["class"] = string.Join(" ", classList);
    }
    else
    {
        attributes.Add("class", requiredClass);
    }

    return html.LabelFor(expression, resolvedLabelText, attributes);
}

Then you can style the class:

.required-label::after { content : "*" }

Questions:
Answers:

I hobbled this together from some other posts:

It works for me since the labelfor is followed by an input plus a span (the input the label is for, and the validation span)

input[data-val-required]+span:before {
  content: "*";
  font-weight: bold;
  color: red;
  position:relative;
  top:-34px;
  left:-12px;
  font-size:14pt;
}

Questions:
Answers:

Based on the above answer by Renato Saito along with the comments, as well as adding $(document).ready and checking to make sure that we are not adding more than one asterisks (I’m getting that on some of my fields for some reason), I have this:

// Add asterisks to required fields
$(document).ready(function() {
    $("[data-val-required]").each(function () {
       var label = $('label[for="' + $(this).attr("id") + '"]');
        var asterisksHtml = '<span style="color:red">&nbsp;*</span>';
        if (label.text().length > 0 && label.html().indexOf(asterisksHtml) === -1) {
            label.append(asterisksHtml);
        }
    });
});