If you wish to modify a property value on the list item during the event, the value should be updated in After Properties property of the properties parameter.Share Point reads these values from the event parameter and modifies the item accordingly when the actual operation runs (e.g. Current inside such methods as Item Added, Item Updated and so on as they are usually asynchronous and might be executed on any machine of Share Point farm. Current is null within synchronous Item Adding, Item Updating, etc. On the other hand, within the constructor of SPItem Event Receiver the Http Context. So, the possible workaround here is to get current Http Context inside the constructor, save it in a variable and then use in synchronous methods.object will be used for both the updating and updated events, and that instance won't be reused in the context of a separate update. To String() since it converts nulls to empty strings. At that point you will not have Before Properties to compare to.Although asynchronous events expose a SPItem Event Properties parameter named properties just like their synchronous counterparts, remember that the operation has already completed so you cannot modify anything in the properties parameter (well, you can, but it doesn’t do anything).Additionally, the properties parameter may not be populated with information that you would tend to expect to be present.A for Apple, A for Asynchronous and A for After events, so all Asynchronous events occur after the event, which does not stop the code to execute.
Another limitation of v2 event handlers is that you can only catch events on document and forms libraries. Now, WSS v3 has a vastly increased number of events developers can take advantage of.
A developer could catch the event and perform some action.
Unfortunately for v2 developers, all of the event handlers were "after the fact" handlers.
These events include "before the fact" or synchronous events as well as "after the fact" or asynchronous events as illustrated in Figure 1.
As a developer interested in catching Share Point events, you are no longer limited to only document libraries and forms libraries.