These events could be web events (Web Adding, Web Provisioned, Web Deleting etc), feature events (Feature Activated, Feature Deactivated etc) or most popularly, list item events (Item Updated, Item Updating, Item Added etc).
Before Properties and After Properties are available for the different event receiver classes.
Changed value means that the correct updated value was available.
Original value means that the correct original value was available.
When dealing with event receivers in Share Point custom code, we use the Before Properties and After Properties to get a hash table of properties consisting of string/value pairs that correspond to fields in the SPItem object before and after the event occurred respectively.
Share Point has a built-in infrastructure that allows certain SP objects to raise events that can be handled by custom code.
Users can change data like the number of moons or the distance to the earth, but they are not able to change the name of the planet.For 5 successive years I’ve been rewarded as Share Point Server MVP for my contribution to the Share Point community: I developed the U2U CAML Query Builder and its successor the CAML Designer, which I develop together with Andy Van Steenbergen.In the many years I worked for U2U, I worked as technical assistant for Patrick Tisseghem who unfortunately died on 3th September 2008.You could think that the current values are stored in the Before Properties of the item but that’s not true: the Before Properties are unreliable at this point. When the name of the planet is changed, the update is canceled and an error message is returned to the user.If the name isn’t changed, the changes are saved to the Share Point list.To prevent users from changing the name of the planet, you can develop a Item Updating event receiver.This event occurs before the data is saved to the Share Point list.I’m Karine Bosch and currently I’m working as Share Point Solution Architect for Recomatics, a company located in Destelbergen near Ghent.Previously I worked as a Premier Field Engineer for Share Point @ Microsoft Belgium.Also it can fire twice in case of doc library/list if we are updating the current item values with in this item updating event. https:// @Robert about the before properties, yes your right they would be the same regardless.... You can also use event receivers to validate the data that the user wants to change.It is particularly difficult to do this yourself in an event receiver in Share Point because you typically don’t have any context to work with.It turns out there is actually a very simple way to accomplish this, but it’s not clearly documented in the places you would expect it.For both lists and libraries: No value means that column value in the hash table was not available.