Registering SharePoint Event Handlers

The first thing you want to do if you are writing event handlers for SharePoint is download the VSeWSS 1.1. This has a whole bag of goodies for us SharePoint developers  including a nice template for creating event handlers. Unfortunately it is only available in VS2005.

There are basically two ways you can register an event handler to a SharePoint list or content type.

1. Features - declarative approach
2. Features and OM combined

Ok, so when would you use one instead of the other.

1. Features
   Basically you can use the Features declarative model when you want to register an event handler to all lists of the same type (ListTemplateId). If the ListTemplateId = 101 (Document Library) as shown below then when the Feature is installed and activated then the event handler will associated to all document libraries in the site.
   Everything is declared in the ElementsManifest.xml file.
   <Elements>
     <Receivers ListTemplateId=”101″>
       <Receiver>
         <Name>SimpleEvent</Name>
         <Type>ItemAdded</Type>
         <SequenceNumber>10000</SequenceNumber>
         <Assembly>SimpleEventHandler, Version=1.0.0.0, Culture=neutral,
           PublicKeyToken=10b23036c9b36d6d</Assembly>
         <Class>CJ.Samples.SimpleEventHandler</Class>
         <Data></Data>
         <Filter></Filter>
       </Receiver>
     </Receivers>
   </Elements>Notes:
   ListTemplateId: This specifies which list to associate the event handler. 101 = document library. This is an all or nothing approach which means I can not associate the event handler to only one document library.
   ItemAdded: This is the event that will be raised when this action takes place.
   //Override the ItemAdded event and add your own code
        public override void ItemAdded(SPItemEventProperties properties)
        {
            SetSecurityForNewItem(properties.ListItem.File, properties.ListItem.ParentList);
        }
   Assembly, PublicKey Token, Class: Self explanatory. The event handler must be installed in the GAC before is can be associated to a list.
   SequenceNumber: This allows you to have multiple event handlers registered and specifiy their order of execution.
   Data
   Filter
2. Features and Object Model
   In this approach we have the ability to register our event handler to only one (or more) list/content type. Our solution (.wsp) would manage the process of installing our event handler assembly into the GAC and activate the Feature. When the Feature is activated we can run a Feature Receiver to attach our event handler to a specified list as shown below.

public override void FeatureActivated(SPFeatureReceiverProperties properties)
{
    SPWeb web = properties.Feature.Parent as SPWeb;
    web.Lists["Appointments"].EventReceivers.Add(
      SPEventReceiverType.ItemAdded,
      “CJ.SharePoint.Eventhandlers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=3a29000ff02kt1bn”,
      “CJ.SharePoint.Eventhandlers.ItemPermissionsEventHandler”);
}

Side note on Event Handlers
If the event handler modifies the current list or current list item then you must call the this.DisableEventFiring() method before committing the change, and then before you leave your event handler code call this.EnableEventFiring() method to turn events back on. This stops recursive event firing from occurring where the list item is being modifed by the event handler which in turn raises the event handler again, thus causing an infinite loop.