Creating an PagedList<T> that uses AJAX
I’ve been using this PagedList functionality that i found from a blog article Rob Conery put up, and a control I found by Robert Muehsig which I’ve really enjoyed using so far.
One of the things that was missing from the functional set that I ended up needing was the ability to page the list, but through issuing AJAX requests instead of the typical post back.
So I went off and extended the existing model to support AJAX requests, and thought I would share it in case anyone else needed to do the same thing.
I guess the best place to start would be the use case. So to start I created a control that encapsulates the Paging UI layout and calls I need. The use of the original control looks like this:
Html.RenderPartial("AjaxPagination",
new AjaxPaginationViewData
{
PageIndex = Model.PageIndex,
Action = "CondoPage",
Controller = "Home",
AjaxOptions =
new AjaxOptions { UpdateTargetId = "updatedContent" },
TotalCount = Model.TotalCount,
PageSize = Model.PageSize,
NumberOfPagesToEachSide = 2
}
);
The new AJAX functionality is called similarly:
<% using (Ajax.BeginForm("SomePage",
"SomeController",
new AjaxOptions { UpdateTargetId = "updatedContent" })) { %>
<% Html.RenderPartial("AjaxPagination",
new AjaxPaginationViewData {
PageIndex = Model.PageIndex,
Action = "SomeAction",
Controller = "SomeController",
AjaxOptions = new AjaxOptions
{ UpdateTargetId = "updatedContent" },
TotalCount = Model.TotalCount,
PageSize = Model.PageSize,
NumberOfPagesToEachSide = 2
});%>
<% } %>
A couple things to note. You’ll notice that the AJAX control is rendered inside a Ajax.BeginForm. This is because I’m using the Microsoft.Ajax way of making AJAX calls. This could also be done using jQuery or something else that can process AJAX calls. I just went this way because the scripts are already included in asp.net mvc app when you first create the project. The result of the AJAX call will be a partial view, and we’ll need to put that somewhere. That’s where the UpdatedTargetId comes into play. Other things we include in the AJAX control that are not in the original are the Action and the Controller, and some AjaxOptions. PageActionLink doesn’t work with the AJAX control, because we’ll be using Ajax.ActionLink to build the link, which is why I broke it up into Action, and Controller. For the AjaxOptions, we need those to specify the target of the call.
So now that’s been explained, let’s look at the controls themselves. Here’s a comparison of the original control and the ajax control.
The original is one this way:
<% if (Model.HasPreviousPage) { %>
<a href="<%=Model.PageActionLink.Replace("%7Bpage%7D", (Model.PageIndex - 1).ToString())%>">Previous</a>
<% } %>
<% if (Model.GetFirstPageToLink() != 1) { %>...<% } %>
<%for (var page = Model.GetFirstPageToLink(); page <= Model.GetLastPageToLink(); page++) {
if (page == Model.PageIndex) { %>
<%=page.ToString()%>
<% } else { %>
<a href="<%=Model.PageActionLink.Replace("%7Bpage%7D", page.ToString())%>"><%=page.ToString()%></a>
<% }
if (page != Model.GetLastPageToLink()) { %>|<% } } %>
<% if (Model.GetLastPageToLink() != Model.PageCount) { %>...<% } %>
<% if (Model.HasNextPage) { %>
<a href="<%=Model.PageActionLink.Replace("%7Bpage%7D", (Model.PageIndex + 1).ToString())%>">Next</a>
<% } %>
And the AJAX control is done this way:
<% if (Model.HasPreviousPage) { %>
<%= Ajax.ActionLink("Previous", Model.Action, Model.Controller, new { page = (Model.PageIndex - 1).ToString() }, Model.AjaxOptions)%>
<% } %>
<% if (Model.GetFirstPageToLink() != 1) { %>...<% } %>
<%for (var page = Model.GetFirstPageToLink(); page <= Model.GetLastPageToLink(); page++) {
if (page == Model.PageIndex) { %>
<%=page.ToString()%>
<% } else { %>
<%= Ajax.ActionLink(page.ToString(), Model.Action, Model.Controller, new { page = page.ToString() }, Model.AjaxOptions)%>
<% } if (page != Model.GetLastPageToLink()) { %> | <% } } %>
<% if (Model.GetLastPageToLink() != Model.PageCount) { %>...<% } %>
<% if (Model.HasNextPage) { %>
<%= Ajax.ActionLink("Next", Model.Action, Model.Controller, new { page = (Model.PageIndex + 1).ToString() }, Model.AjaxOptions)%>
<% } %>
The big difference here is the way that the links are generated. The original control simply creates an anchor tag and passes in the url generated by the Model. The AJAX control uses AJAX.ActionLink() instead, so we can have the link support AJAX.
So knowing how the control looks, this is the Model for the AJAX control itself:
public class AjaxPaginationViewData
{
public int NumberOfPagesToEachSide { get; set; }
public int PageIndex { get; set; }
public int PageSize { get; set; }
public int TotalCount { get; set; }
public string Action { get; set; }
public string Controller { get; set; }
public AjaxOptions AjaxOptions { get; set; }
public int PageCount
{
get
{
return (int)Math.Ceiling((double)TotalCount / PageSize);
}
}
public bool HasPreviousPage
{
get
{
return (PageIndex > 1);
}
}
public bool HasNextPage
{
get
{
return (PageIndex * PageSize) <= TotalCount;
}
}
public int GetFirstPageToLink()
{
return (PageIndex - NumberOfPagesToEachSide > 1 ? PageIndex - NumberOfPagesToEachSide : 1);
}
public int GetLastPageToLink()
{
return (PageIndex + NumberOfPagesToEachSide < PageCount ? PageIndex + NumberOfPagesToEachSide : PageCount);
}
}
That pretty much explains how the control is built.
The only thing left is how the interaction with PagedList happens. For that we look at the action that the control calls. In this example, we’re calling SomeAction in SomeController, and it would look something like this:
public ActionResult SomeAction(int page)
{
CachedPage = page;
var query = GetSearchQuery(CachedSearchParameters);
var model = query.ToPagedList(page, DefaultPageSize);
return PartialView("AjaxResults", model);
}
The ToPagedList performs the functionality that is included with the PagedList classes which you can find here.
Let me know what you think, and if you’d like some demo source to see this in action I can happily provide, just let me know.
hi,
Thanks for the guide, but I think some explanation is missing at the last step. Where is DefaulPagerSize and CachedPage declared (session?)? What/where is the logic of the method GetSearchQuery(); ?
Thanks
//david
In my implementation, DefaultPageSize is just a constant I have, and CachedPage is a property that’s hitting a stored session value. This is completely up to you, however, which is why I left it out.
Also, the logic from GetSearchQuery is left out as well, because that’s implementation specific. For the first project I worked on, that returned utilized IQueryable and LINQ 2 SQL, but I’ve had others that use various other things just as NHibernate, Entity Framework, etc.
Thanks for your reply! I see… Thats where I should get the data I want to display from my db. Im rather new to ajax in general so I dont really get the connection how the query object can reference the ToPagedList() method, which is in the PagedListExtensions class…? Perhaps I just need to read more about ajax.
I would be really happy to have a sample/demo source (if possible) to see things more clearly.
Thanks again!
//David
Hi,
What is the point of having the ajax call in a Ajax.Beginform? When is the form supposed to be submitted? What I can see it is the actionslinks in the pager that calls the controller action…?
Hey David, that’s a good question. To be honest I can’t remember why I put it inside an Ajax.BeginForm. I think I used the Ajax.BeginForm to actually wrap the Ajax functionality so I wouldn’t have to handle the click event manually using jQuery or something. Otherwise, when the user clicks on the actionlink, it would end up making a regular HTTP POST and it wouldn’t be AJAX.
When I get some more time I’ll throw up an example of how I did this on GitHub so you can take a look at it. When I do that I’ll probably make a new post about it being there, so be on the lookout.
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