How to find which control made the asyncpostback?

I know how to find which control made the postback, it's something like:

string postBackControl = Request.Params.Get("__EVENTTARGET") == null ? string.Empty : Request.Params.Get("__EVENTTARGET开发者_运维知识库");

but how can I find the one that made async postback?

Have you tried this...

Which control raised the async postback event?