HtmlHelper Extensions

HtmlHelperExtensions.cs

namespace Web.Extensions.Control
{
  public static partial class HtmlHelperExtensions
  {
    // Usage: @Html.ListBoxWithAttributesFor(m => m.Foo, Model.Foos, false)
    // See SelectListItemWithAttributes
    public static MvcHtmlString ListBoxWithAttributesFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItemWithAttributes> selectList, bool multiple = true)
    {
      if (expression == null)
    	{
    		throw new ArgumentNullException("expression");
    	}
    
    	var metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
    	var name = ExpressionHelper.GetExpressionText(expression);
    	var fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
    
    	var listItemBuilder = new StringBuilder();
    
    	if (selectList != null)
    	{
    		selectList.ForEach(item => listItemBuilder.AppendLine(ListItemToOption(item)));
    	}
    
    	var tagBuilder = new TagBuilder("select") { InnerHtml = listItemBuilder.ToString() };
    
    	if (multiple)
    	{
    		tagBuilder.MergeAttribute("multiple", "multiple");
    	}
    
    	tagBuilder.MergeAttribute("name", fullName, true /* replaceExisting */);
    	tagBuilder.GenerateId(fullName);
    
    	// If there are any errors for a named field, we add the css attribute.
    	ModelState modelState;
    	if (htmlHelper.ViewData.ModelState.TryGetValue(fullName, out modelState))
    	{
    		if (modelState.Errors.Count > 0)
    		{
    			tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
    		}
    	}
    
    	tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata));
    
    	return MvcHtmlString.Create(tagBuilder.ToString(TagRenderMode.Normal));
    }
    
    private static string ListItemToOption(SelectListItemWithAttributes item)
    {
    	var builder = new TagBuilder("option") { InnerHtml = HttpUtility.HtmlEncode(item.Text) };
    
    	if (item.Value != null)
    	{
    		builder.Attributes["value"] = item.Value;
    	}
    	
    	if (item.Selected)
    	{
    		builder.Attributes["selected"] = "selected";
    	}
    
    	if (item.Attributes != null)
    	{
    		item.Attributes.ForEach(attribute => { builder.Attributes[string.Concat("data-", attribute.Key)] = attribute.Value.ToString(); });
    	}
    
    	return builder.ToString(TagRenderMode.Normal);
    }
  }
}