AynscResult not exist in .net core ?

I'm migrating MVC application into .NET Core that I had to make code change arround AsyncResult class After some basic research I found that AyncResult is not exist in .net core. AsyncResult asyncr=(AsyncResult)ar; Here I'm facing issue with: the type or namespace is not present .your missing namespace. Can anyone please help me . What I have to use insted of ayncResult