Returns an System.Threading.ApartmentState value indicating the apartment state.
One of the System.Threading.ApartmentState values indicating the apartment state of the managed thread. The default is ApartmentState.Unknown.
This method, along with the Thread.SetApartmentState(ApartmentState) method and the Thread.TrySetApartmentState(ApartmentState) method, replaces the Thread.ApartmentState property.