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Event Handlers in WSS v3

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Those that are familiar with event handlers on Document Library lists in WSS v2 will be excited to know that event handlers can now be attached to any type of list. Not only do we get access to the Asynchronous events such as ItemAdded, we now also get access to Synchronous event before the fact, like ItemAdding. This will allow greater control over the way in which lists can be used within WSS v3.

This article will set out to describe the step by step instructions for defining an event handler and then hooking it up to a WSS list.

Creating the event handler

Creating an event handler is extremely simple, use Visual Studio .NET 2005.
1. Add a reference to the Microsoft.SharePoint assembly.

2. Create a class that inherits from one of the new event receiver classes, like SPItemEventReceiver or SPListEventReceiver.

3. Implement an override method for the event you wish to implement. Something like the following;

using Microsoft.SharePoint; public class ListEventHandler : SPItemEventReceiver {   public override void ItemAdded(SPItemEventProperties properties)   {     SPListItem listItem = properties.ListItem;     listItem["ColumnName"] = "Hello";     listItem.Update();   }   public override void ItemDeleting(SPItemEventProperties properties)   {     properties.Cancel = true;     properties.ErrorMessage = "Deleting items from the list is not permitted.";   } }

The ItemAdded event will set a column in the list called “ColumnName” to a value of ‘Hello’ and the ItemDeleting event will be cancelled with an error message displayed to the user.

4. The next step is to sign the assembly and deploy it to the GAC.

That is it; we have created our event handler and deployed it ready to a list to start consuming it. The next step is to register the event to be fired from a given list.

Registering the event handler with the list

In the previous version of WSS you could register the event handler using the SharePoint user interface. This facility has been removed in WSS v3. Registering the event handler in WSS v3 can be done in two ways, as a feature or via code. I will describe the registering via code method. For more information on creating a feature the article called “Working with Features” in the WSS SDK documentation.

The easiest way to register the event handlers against the list is to create a Console application, like the one below;

public class Program {   static void Main(string[] args)   {     SPSite collection = new SPSite("https://server/site/");     SPWeb site = collection.OpenWeb();     SPList list = site.Lists["MyList"];     string asmName = "MyEventHandlers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=f90218d0785d9063";     string className = "MyEventHandlers.ListEventHandler";     // Register the events with the list     list.EventReceivers.Add(SPEventReceiverType.ItemAdded, asmName, className);     list.EventReceivers.Add(SPEventReceiverType.ItemDeleting, asmName, className);     // Clean up the code     site.Dispose();     collection.Dispose();     // Return to calling environment : Success     Environment.Exit(0);   } }
Basically, the code attaches to the SharePoint site and locates the list “MyList” then adds an item to the EventRecievers collection of the list for each event to be fired.

As you can see it is pretty easy to deal with the new event handlers in WSS v3. Happy coding.

Comments

  • Anonymous
    December 06, 2007
    The comment has been removed

  • Anonymous
    December 06, 2007
    Code Jedi Says: April 13, 2007 at 9:21 am Can you please forward me the code and I will have a look for you! (Email me at william.cornwill@hotmail.com)

  • Anonymous
    December 06, 2007
    crucial Says: June 5, 2007 at 4:14 am Would you do the same thing now to implement an event handler on a document library in WSS3?

  • Anonymous
    December 06, 2007
    Code Jedi Says: June 5, 2007 at 9:32 am Document libraries in WSSv3 are also ultimately based on the list architecture. The process described in this article is applicable to any list (of any type) in WSSv3 - So Yes.

  • Anonymous
    December 06, 2007
    jeff Says: June 27, 2007 at 12:23 am How can i remove an event handler added this way? I’ve created several versions of an event handler and it seems that an older version is running, instead of the current one.

  • Anonymous
    December 06, 2007
    jeff Says: June 27, 2007 at 12:37 am Actually, I looked in the Windows/assembly folder and found the other versions still there. using gacutil.exe to install the handler to the GAC seems to have left the other ‘versions’ . When i tried to uninstall using the /u option, it told me that there were none matching the one that i just installed.

  • Anonymous
    December 06, 2007
    jeff Says: June 28, 2007 at 4:30 am hello again, it seems that sharepoint is still wanting to load the other versions as I get an error in the event log that Sharepoint cannot find older versions of the library. Can you help me?

  • Anonymous
    December 06, 2007
    Sriram Says: July 4, 2007 at 6:20 am ItemAdded() and ItemAdding() do not fire/work for lists at sitecolleciton level (”User Information List”).. Any workarounds or why it wouldnt work???

  • Anonymous
    December 06, 2007
    tad Says: August 15, 2007 at 2:24 pm Where to put the console application?

  • Anonymous
    December 06, 2007
    mosza Says: August 16, 2007 at 4:45 pm Hello Tad, you need to put your console app on the server running SharePoint as all related dlls will be available there.

  • Anonymous
    December 06, 2007
    mosza Says: August 16, 2007 at 4:47 pm Jeff, it is common, that altering an assembly requires an iisreset for SharePoint to handle due to caching and all.

  • Anonymous
    December 06, 2007
    Harry Says: September 27, 2007 at 5:46 pm Can anybody give a snap of code for ItemAdding Event for a list/document library??? Thanks in advance.

  • Anonymous
    December 18, 2008
    All -- Please help. How can I completely uninstall, delete, remove my orphaned EventHandler? Similar to Jeff's note above, I have removed all traces of the assemby from the GAC using GacUtil.exe, I have removed all traces from the 12-hive "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions12TEMPLATEFEATURES" folder, I have run an iisreset, rebooted the server, etc, etc, and still I get the error in > Event Viewer, >Application, as: Event Category: General... Event ID: 6644... Event manager error: Could not load file or assembly 'Cti.Pmp.DocumentLibraryEventHandler, Version=1.0.0.3, Culture=neutral, PublicKeyToken=ee325f760b9d530e' or one of its dependencies. The system cannot find the file specified. One of the problems that I have is that this assembly was installed with the wrong version and the wrong PublicKeyToken, so I suspect that is part of the issue. But, I need to fix it. How can this be fixed? Is it possible to uninstall by version? Thank you. -- Mark Kamoski