(Homework) MVC Pagination Help

I'm attempting to put together a very simple application using ASP.NET MVC that shows news articles and paginates them. I'm sort of half-way there but need some help sorting out the pagination and getting it to work with the search query.

Here is my HomeController:

public ActionResult Index(String query, int? page)
{
        // limit the number of articles per page
        const int pageSize = 4;
        // build the query
        var ArticleQuery = from a in _db.ArticleSet select a;
        // check if their is a query
        if (!string.IsNullOrEmpty(query))
        {
            ArticleQuery = ArticleQuery.Where(a => a.headline.Contains(query));
        }
        // orders the articles
        var OrderedArticles = ArticleQuery.OrderByDescending(a => a.posted);
        // takes the ordered articles and paginates them
        //var paginatedArticles = new PaginatedList(OrderedArticles.Skip((page ?? 0) * pageSize).Take(pageSize), page ?? 0, pageSize);
        var paginatedArticles = new PaginatedList<Article>(OrderedArticles, page ?? 0, pageSize);
        // return the paginated articles to the view
        return View(paginatedArticles);
}

The idea is that the Controller shows 4 items per page will order them by date. Here is the View I have for the Index method:

<ul id="pagination">
    <% if (Model.PreviousPage) { %>
        <li><%= Html.ActionLink("<< First Page", "Index")%></li>
        <li><%= Html.ActionLink("<< Previous Page", "Index", new { page=(Model.PageIndex-1) }) %></li>
    <% } %>
    <% if (Model.NextPage) { %>
        <li><%= Html.ActionLink("Next Page >>", "Index", new { page = (Model.PageIndex + 1) })%></li>
        <li><%= Html.ActionLink("Last Page >>", "Index", new { page = (Model.TotalPages - 1) })%></li>
    <% } %>    
</ul>

The idea is that these two pagination links will only show if the conditions are true.

Finally here is the PaginatedList class for the pager:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;

namespace NewsApp.Models
{
    public class PaginatedList<T> : List<T>
    {
        public int PageIndex { get; private set; }
        public int PageSize { get; private set; }
        public int TotalCount { get; private set; }
        public int TotalPages { get; private set; }

        public PaginatedList(IQueryable<T> source, int pageIndex, int pageSize)
        {
            PageIndex = pageIndex;
            PageSize = pageSize;
            TotalCount = source.Count();
            TotalPages = (int)Math.Ceiling(TotalCount / (double)PageSize);

            this.AddRange(source.Skip(PageIndex * PageSize).Take(PageSize));
        }
        public bool HasPreviousPage
        {
            get
            {
                return (PageIndex > 0);
            }
        }
        public bool HasNextPage
        {
            get
  开发者_运维技巧          {
                return (PageIndex + 1 < TotalPages);
            }
        }
    }

NOTE: I' don't want to use any 3rd party components like MVCContrib etc as this is for a University assignment so would defeat the purpose.

The pagination works fine now but when I do a search and have e.g. /?query=test I want to be able to page the results, at the moment they get lost :/

Thanks.

You didn't cite what you're actual error is, but I think I see what's wrong:

These two lines will return your an IEnumerable containing your results.

var paginatedArticles = OrderedArticles.Skip((page ?? 0) * pageSize).Take(pageSize).ToList();

return View(paginatedArticles);

However, based on your view and the helper class you posted, you're view is expecting PaginatedList object as its Model.

If that's the case, I'd do the following (updated):

var paginatedArticles = new PaginatedList( OrderedArticles, page ?? 0, pageSize );

return View(paginatedArticles);

And then your view should have the proper model being returned to it.

That said: I don't know why you aren't using a repository layer, but unless your app is only a single page it is almost always a good idea to have one in place.

Update --here's what I think the full controller logic should be:

public ActionResult Index(String query, int? page)
{
    const int pageSize = 4;

    var ArticleQuery = from m in _db.ArticleSet select m;

    // Searching
    if (!string.IsNullOrEmpty(query))
    {
        ArticleQuery = ArticleQuery.Where(m => m.headline.Contains(query));
    }

    var OrderedArticles = ArticleQuery.OrderByDescending(m => m.posted);

    var paginatedArticles = new PaginatedList( OrderedArticles, page ?? 0, pageSize );
    // this will now be of type paginatedList. this class handles all of the paging for you, so no need to do that ahead of time

    return View(paginatedArticles);
}

In this case, PaginatedList is NOT a helper --its a full on class that needs to be created and passed to your model. A helper in the strict definition of the word is done much differently and probably wouldn't work in your case here.