Can the ItemAdding event be used in a Sandbox?
I need to perform a task when a Item is a added/adding, it has to be synchronous (item added is async so i cant use that).
If i cant use the ItemAdding what other options do i have?
Yes, it is possible (see here too http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spitemeventreceiver.itemadded(v=office.14).aspx), however you would need to be aware of some tips, such as:
I don't know the answer about using ItemAdding in Sandbox (although my guess would be yes), but another option you have is to change ItemAdded to be synchronous.
Here are a couple posts about that: