PortablePrism.Portable by Andrii Chebukin

<PackageReference Include="PortablePrism.Portable" Version="1.0.1" />

 IEventHandlerManager

public interface IEventHandlerManager
Handles management and dispatching of EventHandlers in a weak way.
void AddReferenceHandler(ref List handlers, EventHandler handler, int defaultListSize)

Adds a handler to the supplied list in a weak way.

void CallReferenceHandlers(object sender, List<WeakReference> handlers)

Invokes the handlers

Removes an event handler from the reference list.