.NET FOLLOWER

    In our SharePoint 2007 application, there was a custom upload page for a document library. The custom upload page was derived from the Microsoft.SharePoint.ApplicationPages.UploadPage defined in the Microsoft.SharePoint.ApplicationPages.dll. Within application web pages, all links to the upload page were direct, while the page itself was located in the _layouts folder. After migration to the SharePoint 2010, I’ve found out that every request to the custom upload page is transferred to the Uploadex.aspx (located in the _layouts folder as well): the URL in browser corresponds to our upload page, but the content corresponds to the Uploadex.aspx. After a short investigation by means of .Net Reflector I found the reason in the UploadPage base class defined in Microsoft.SharePoint.ApplicationPages.dll, Version=14.0.0.0. Let’s take a look at the OnPreInit method of the UploadPage:

protected override void OnPreInit(EventArgs e)
{
    if (!this.customPage)
    {
        string customUploadPage = base.Web.CustomUploadPage;
        if (!string.IsNullOrEmpty(customUploadPage))
        {
            try
            {
                base.Server.Transfer(customUploadPage);
            }
            catch (Exception)
            {
            }
        }
    }
    base.OnPreInit(e);
}

*Note: this code was added in SharePoint 2010 and wasn’t presented in SharePoint 2007

As we can see, the SharePoint 2010 itself allows to define the CustomUploadPage for a website. If it’s defined, the UploadPage automatically transfers every request to it. Apparently, after migration the CustomUploadPage was somehow set to _layouts/Uploadex.aspx. Another interesting moment here is the customPage boolean field, which acts as marker indicating whether the current page is the custom upload page or not.

Probably, the acceptable solution for our issue would be to set the CustomUploadPage property of the SPWeb object to the URL of our own custom upload page. But, firstly, the problem here is that our upload page derived from the UploadPage doesn’t know that it’s a custom one as the customPage field is set to false by default. Thus, without any code modification, we will have a kind of loop here, because our custom page due to the UploadPage base class will be transferring the request to itself infinitely. Secondly, I don’t want to rely on the CustomUploadPage property, which can be unexpectedly changed. I just want when I click on the direct link to our upload page, this page would be opened without any sudden redirections and transfers.

So, the best solution is to set the customPage field to true within the constructor of our custom upload page. No transfer happens in this case, and we don’t need to deal with the CustomUploadPage at all. In our case It looks like:

public class MyUploadPage : UploadPage
{
    // ...
    public MyUploadPage()
    {
        customPage = true;
    }
    // ...
}

That’s all!