Set content type based on file extension after uploading into document library

Question

when there are multiple content types associated with a document library, say, report builder report, and excel documents, after you drag and drop a document into the document library, content type will not be detected based on the file extension. Suppose
your default content type is document, and you had added the report build report content type, and you uploaded a .RDL file, the content type for the file will be set to the default document content type.
I get a requirement to update the content type automatically based on the file extension, what follows is my code:
public class setCNTByFileExtItemAdded : SPItemEventReceiver
/// <summary>
/// An item was added.
/// </summary>
public override void ItemAdded(SPItemEventProperties properties)
if (properties.Web.GetFile(properties.AfterUrl).Exists)
SPListItem CurrentListItem = properties.Web.GetFile(properties.AfterUrl).Item;
String FileName = CurrentListItem.Name;
if (FileName.EndsWith(".rdl",StringComparison.OrdinalIgnoreCase))
CurrentListItem.Properties["ContentTypeId"] = "0x010100C3676CDFA2F24E1D949A8BF2B06F6B8B";
CurrentListItem.SystemUpdate(false);
base.ItemAdded(properties);
What follows are references that helped me:
http://stackoverflow.com/questions/7984300/properties-listitem-is-null-in-itemadded-event-while-uploading-documents-using
http://williamvanstrien.blogspot.in/2011/10/read-content-of-uploaded-file-within.html
http://blogs.msdn.com/b/manuj/archive/2009/09/22/itemadded-event-on-document-library-the-file-has-been-modified-by-on-error.aspx
http://support.microsoft.com/kb/2647429

Answer 1

user may have further requirement to detect whether the uploaded .xlsx file contains powerpivot data model, i tried the following code, the caveat is that .xlsx is actually a zip file, i just test whether the uploaded stream contains an entry xl/model/item.data.
public partial class ApplicationPage2 : LayoutsPageBase
protected void Page_Load(object sender, EventArgs e)
if (this.IsPostBack)
if (FileUpload1.PostedFile == null)
return;
string destWeb = DestinationUrl.Url;
string destUrl = destWeb + "/" + FileUpload1.FileName;
using (SPSite site = new SPSite(destWeb))
using (SPWeb web = site.OpenWeb())
SPFile f = web.Files.Add(destUrl, FileUpload1.PostedFile.InputStream);
if (FileUpload1.FileName.EndsWith(".xlsx") )
Stream fs = f.OpenBinaryStream() as Stream;
using (ZipArchive zfs = new ZipArchive(fs, ZipArchiveMode.Read))
if (zfs.GetEntry("xl/model/item.data") == null)
Debug.WriteLine("Does not contain data model");
else
Debug.WriteLine("Contain data model");
The code i posted here is part of an application page in layout folder, the reason why i use application page is described in
http://social.msdn.microsoft.com/Forums/sharepoint/en-US/065d010a-d37e-4da4-9873-172ab2c50d6d/custom-list-new-application-page-with-listfielditerator-and-savebutton?forum=sharepointdevelopment#288a686e-bfbe-41aa-83d0-58a80f0cec07