Using @Html.DisplayNameFor() with PagedList

问题:

I've been trying out the PagedList package to get paging for my index views. Everything was going well, and at the controller level everything is working fine, it only displays 5 records per page, and displays the appropriate page based on the querystring.

My problem is in the view. I changed the @Model to PagedList.IPagedList so I could access the Model.HasNextPage and other properties, but now the @Html.DisplayNameFor(model => model.ItemName) are no longer working. I get this error:

PagedList.IPagedList<Dossier.Models.Item>' does not contain a definition for 'ItemName' and no extension method 'ItemName' accepting a first argument of type 'PagedList.IPagedList<Dossier.Models.Item>' could be found (are you missing a using directive or an assembly reference?)

Here are the relevant parts of the view:

@model PagedList.IPagedList<Dossier.Models.Item>
@using Dossier.Models.Item

...

<th>
    @Html.DisplayNameFor(model => model.ItemName)
</th>

It seems IPagedList is not compatible with DisplayNameFor(). Any idea why this is happening, and how I could fix it? I know I could just manually enter the column names, but I'd like for that information to stay (and be changeable) in the model later.

回答1:

You can try this

@Html.DisplayNameFor(model => model.FirstOrDefault().ItemName)

回答2:

As an alternate solution to the accepted answer, remember that IPagedList inherits from IEnumerable. That means that you could write:

@model IEnumerable<Dossier.Models.Item>

At the beginning of the page, and just cast the model to IPagedList when needed:

@Html.PagedListPager((IPagedList)Model, page => Url.Action("Index", new { page = page }))

You can even declare the casted variable in the header, in order to use it multiple times within the page:

@{
    ViewBag.Title = "My page title";
    var pagedlist = (IPagedList)Model;
}

This would allow you to use the DisplayNameFor helper method, and access all PagedList methods/properties, without the need for dummy elements nor calling .FirstOrDefault() for each field.

回答3:

I solved the problem by creating an overload of DisplayNameFor that accepts a IPagedList<TModel>.

namespace PagedList.Mvc
{
    public static class Extensions
    {

        [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
        public static MvcHtmlString DisplayNameFor<TModel, TValue>(this HtmlHelper<IPagedList<TModel>> html, Expression<Func<TModel, TValue>> expression)
        {
            return DisplayNameForInternal(html, expression);
        }

        [SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", Justification = "This is an extension method")]
        internal static MvcHtmlString DisplayNameForInternal<TModel, TValue>(this HtmlHelper<IPagedList<TModel>> html, Expression<Func<TModel, TValue>> expression)
        {
            return DisplayNameHelper(ModelMetadata.FromLambdaExpression(expression, new ViewDataDictionary<TModel>()),
                                     ExpressionHelper.GetExpressionText(expression));
        }

        internal static MvcHtmlString DisplayNameHelper(ModelMetadata metadata, string htmlFieldName)
        {
            string resolvedDisplayName = metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();

            return new MvcHtmlString(HttpUtility.HtmlEncode(resolvedDisplayName));
        }
    }
}

I'll be sending a pull request to PageList project to include it into the project for everyone.

回答4:

You do not need to change @Html.DisplayNameFor. Declare model in the view as:

@model IEnumerable<Dossier.Models.Item>

Just move your pager to partial view (lets name it "_Pager"):

@model IPagedList

...

@Html.PagedListPager(Model, 
   page => Url.Action("Index", new { page, pageSize = Model.PageSize }))

...

Render the pager in your view:

@Html.Partial("_Pager", Model)

Thats it.

P.S. You can create Html helper instead of partial view...

回答5:

As an alternate solution you could try:

@Html.DisplayNameFor(x => x.GetEnumerator().Current.ItemName)

It will work even if the list is empty!