koobas.hobune.stream
Action contravarience issue, throwing ArgumentException: Incompatible Delegate Types
I am attempting to define an event as a part of an interface, but have derived types implement more derived versions of that event while still allowing classes accessing the derived type through the interface to subscribe to the event. My code looks something like this:
public interface IWorkItem {
event Action<IWorkItem> WorkCompleteEvent;
}
public class Task : IWorkItem {
public event Action<Task> TaskCompleteEvent;
event Action<IWorkItem> IWorkItem.WorkCompleteEvent
{
add
{
TaskCompleteEvent += value;
}
remove
{
TaskCompleteEvent -= value;
}
}
}
public class SubscriberClass
{
void Subscribe()
{
IWorkItem myWorkItem = new Task();
myWorkItem.WorkCompleteEvent += OnWorkComplete; // This line throws the exception
}
void OnWorkComplete(IWorkItem workItem)
{
// Do Stuff
}
}
But when this code gets called , I get an exception that Action<Task> and Action<IWorkItem> are incompatible delegate types.
According to the C# documentation this should be legal with Action<T> in .NET Framework 4. Unity's API compatibility is set to .NET 4.x
Have you tried:
myWorkItem.WorkCompleteEvent += new Action<IWorkItem>(OnWorkComplete);
If that doesn't work, I would recommend to define your own delegate type for your IWorkItem interface:
public delegate void OnWorkCompletedEvent(IWorkItem aItem);
and also make sure you actually create an instance of your explicit delegate. See this SO question for more details
