More about SharePoint eventhandling

Bas — Fri, 30 Jan 2009 09:18:00 GMT

As I had problems with the way events worked, I wanted to know more about the way they worked. below is bit of information about events that is good to know:

There are two different kinds of events: Synchronous and Asynchronous events.

Synchronous events
- End with -ing (ItemAdding, ItemUpdating)
- Block the code as long the events arent finished
- Can (thus) make use of Session vars (HttpContext.Current is available), because they run in the same session
- Can be used to prevent the event being finished. For example, with the ItemUpdating event you can verify the content being updated. Is the update not valid, the SPItemEventProperties.Cancel can be set to true and the SPItemEventProperties.ErrorMessage can be filled with an error message. This error message will not be displayed, but is written to the logfile. An error page will appear.
- dont contain the SPListItem in it's SPItemEventProperties so when you want to make changes to any of it's field you need to make use of the SPItemEventProperties.AfterProperties (see message below). In the case of itemUpdating, the "old" SPListItem will be used
Asynchronous events
- End with -ed (ItemAdded, ItemUpdated)
- Dont block the code.
- Can't (thus) make use of the Session (HttpContext.Current is null, because code is run in another context)
- Can't be reverted; When these events are fired, the item is already added, updated or deleted.
- contains the SPListItem. Changes can be made if you want to. This fires the (for example) ItemUpdating and ItemUpdated event. This can be turned off by using this.DisableEventFiring();
- When creating a new list, events like FieldAdded and FieldAdding are not fired!

SharePoint events: modify SPListItem fields with vars from the Session in the itemAdding or itemAdded events

Bas — Fri, 30 Jan 2009 08:59:00 GMT

Some time ago I tried to alter a field of a SPListItem right after the moment that the item has been created. A var was stored in the Session so it could be used on the newly created SPListItem (itemAdded).

NOT.

I figured out that the HttpContext isn't available when during the ItemAdded event. When using the itemAdding event, the HttpContext is available, but the item that will be created, isnt. The SPFeatureReceiverProperty.SPListItem is null, because the item is not yet created. After reading the MSDN documentation I figured out that the SPFeatureReceiverProperties Afterproperties can be used to store a value, which will be applied right after the item is created.

below is an example:

    1 public class ItemEventReceiver : SPItemEventReceiver
    2 {    
    3     public ItemEventReceiver()
    4     {
    5         hContext = HttpContext.Current;
    6     }
    7 
    8     /// <summary>
    9     /// overrides default ItemAdded
   10     /// </summary>
   11     /// <param name="properties"></param>
   12     public override void ItemAdded(SPItemEventProperties properties)
   13     {
   14         Debug.WriteLine("ItemAdded");
   15         CheckHContextAndSPListItem(properties.ListItem);
   16         base.ItemAdded(properties);
   17     }
   18 
   19     /// <summary>  
   20     /// overrides the standard ItemAdding
   21     /// </summary>  
   22     /// <param name="properties"></param>  
   23     public override void ItemAdding(SPItemEventProperties properties)
   24     {
   25         string internalFieldName = null;
   26         string FIELD_NAME = "Foo";
   27         SPFieldLookupValue lookupField = null;
   28 
   29         Debug.WriteLine("ItemAdding");        
   30         CheckHContextAndSPListItem(properties.ListItem);
   31 
   32         using (SPWeb web = properties.OpenWeb())
   33         {
   34             internalFieldName = web.Lists[properties.ListId].Fields[FIELD_NAME].InternalName;
   35         }
   36 
   37         // example for adding a value to a SPListItem property
   38         string tempValue = "foo";
   39         properties.AfterProperties[internalFieldName] = tempValue;
   40     }
   41 
   42     /// <summary>  
   43     /// checks the values of hContext and SPListItem  
   44     /// </summary>  
   45     /// <param name="SPListItem">SPListItem out of the SPItemEventProperties</param>  
   46     private static void CheckHContextAndSPListItem(SPListItem listItem)
   47     {
   48         if (HttpContext.Current == null)        
   49             Debug.WriteLine("hContext is null");        
   50         else        
   51             Debug.WriteLine("hContext is available");        
   52 
   53         if (listItem == null)        
   54             Debug.WriteLine("listItem is null");        
   55         else        
   56             Debug.WriteLine("listItem is available");        
   57     }
   58 }     

BBB - Bas Blogging 'Bout SharePoint : Eventhandler

More about SharePoint eventhandling

SharePoint events: modify SPListItem fields with vars from the Session in the itemAdding or itemAdded events