MvcAnnotationHelper: Helps output formatted HTML from model properties.

MvcAnnotationHelper.cs

//-----------------------------------------------------------------------
// <copyright file="MvcAnnotationHelper.cs" company="The Swedish Post and Telecom Authority (PTS)">
//      Copyright (c) 2011, 2012 The Swedish Post and Telecom Authority (PTS)
//      Developed for PTS by Joel Purra <http://joelpurra.se/>
//      Released under the BSD license.
// </copyright>
//-----------------------------------------------------------------------
// https://gist.github.com/2398934

namespace JoelPurra.Web.Helpers
{
    using System;
    using System.Diagnostics.Contracts;
    using System.Linq.Expressions;
    using System.Web.Mvc;
    using System.Web.Mvc.Html;

    /// <summary>
    ///     Helps output formatted HTML from model properties.
    /// </summary>
    public static class MvcAnnotationHelper
    {
        #region Constants and Fields

        private const string DescriptionTagFormat = @"<span class=""description help-inline"">{0}</span>";

        private const string NameTagFormat = @"<span class=""name"">{0}</span>";

        private const string ShortNameTagFormat = @"<span class=""short-name"">{0}</span>";

        #endregion

        #region Public Methods

        /// <summary>
        ///     Gets the data annotation metadata description for a property on the model.
        /// </summary>
        /// <typeparam name="TModel"> The annotated MVC model. </typeparam>
        /// <typeparam name="TValue"> The model property value. </typeparam>
        /// <param name="self"> The html output helper to use. </param>
        /// <param name="expression"> Gets the property on the model to get the annotation from. </param>
        /// <returns> A span tag containing the description. </returns>
        public static MvcHtmlString AnnotatedDescriptionFor<TModel, TValue>(
            this HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression)
        {
            Contract.Requires(self != null);
            Contract.Requires(expression != null);

            return StringFromModel(self, expression, metadata => metadata.Description, DescriptionTagFormat);
        }

        /// <summary>
        ///     Gets the data annotation metadata name for a property on the model.
        /// </summary>
        /// <typeparam name="TModel"> The annotated MVC model. </typeparam>
        /// <typeparam name="TValue"> The model property value. </typeparam>
        /// <param name="self"> The HTML output helper to use. </param>
        /// <param name="expression"> Gets the property on the model to get the annotation from. </param>
        /// <returns> A span tag containing the name. </returns>
        public static MvcHtmlString NameFor<TModel, TValue>(
            this HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression)
        {
            Contract.Requires(self != null);
            Contract.Requires(expression != null);

            return StringFromModel(self, expression, metadata => metadata.DisplayName, NameTagFormat);
        }

        public static MvcHtmlString ShortLabelFor<TModel, TValue>(
            this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
        {
            Contract.Requires(html != null);
            Contract.Requires(expression != null);

            return html.LabelFor(expression, GetPropertyValue(html, expression, metadata => metadata.ShortDisplayName));
        }

        /// <summary>
        ///     Gets the data annotation metadata short name for a property on the model.
        /// </summary>
        /// <typeparam name="TModel"> The annotated MVC model. </typeparam>
        /// <typeparam name="TValue"> The model property value. </typeparam>
        /// <param name="self"> The HTML output helper to use. </param>
        /// <param name="expression"> Gets the property on the model to get the annotation from. </param>
        /// <returns> A span tag containing the short name. </returns>
        public static MvcHtmlString ShortNameFor<TModel, TValue>(
            this HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression)
        {
            Contract.Requires(self != null);
            Contract.Requires(expression != null);

            return StringFromModel(self, expression, metadata => metadata.ShortDisplayName, ShortNameTagFormat);
        }

        #endregion

        #region Methods

        private static string GetPropertyValue<TModel, TValue>(
            HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression, Func<ModelMetadata, string> property)
        {
            ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, self.ViewData);

            string propertyValue = property(metadata);
            return propertyValue;
        }

        /// <summary>
        ///     Extracts and formats a data annotation.
        /// </summary>
        /// <remarks>
        ///     From http://stackoverflow.com/questions/6578495/how-do-i-display-the-displayattribute-description-attribute-value
        /// </remarks>
        /// <typeparam name="TModel"> The annotated MVC model. </typeparam>
        /// <typeparam name="TValue"> The model property value. </typeparam>
        /// <param name="self"> The HTML output helper to use. </param>
        /// <param name="expression"> Gets the property on the model to get the annotation from. </param>
        /// <param name="property"> The data annotation metadata property to use. </param>
        /// <param name="tagFormat"> Formatting string for the output where <code>{0}</code> will be replaced with the value of <paramref
        ///      name="property" /> . </param>
        /// <returns> A user-formatted HTML-string. </returns>
        private static MvcHtmlString StringFromModel<TModel, TValue>(
            HtmlHelper<TModel> self,
            Expression<Func<TModel, TValue>> expression,
            Func<ModelMetadata, string> property,
            string tagFormat)
        {
            Contract.Requires(self != null);
            Contract.Requires(expression != null);
            Contract.Requires(property != null);
            Contract.Requires(tagFormat != null);

            string propertyValue = GetPropertyValue(self, expression, property);

            return MvcHtmlString.Create(string.Format(tagFormat, propertyValue));
        }

        #endregion
    }
}