.Net: CallBack should be on which thread?

Question

I have built a helper class that talks to a JSON service. The class does its work in a background thread. When done, it calls an Action<> CallBack which the client sent it.

Is it best to have the helper class call the Action<> callback on the main UI thread, or should threading be the responsibility of the client?

Answer 1

You should provide a complete synchronous API like object Fetch() and an explicitly marked asynchronous API like void FetchAsnyc(Callback). Maybe your client use a different approach to Multitasking then he can implement this with your synchronous API.

And the UI Thread is really not your scope.