Question

I am trying the following method, but it gives me a compiler error:

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<EventHandler<T>, EventFilter<T>> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}

Question: Why can’t I convert the handler from K to T?

I am using a .net 2.0, because I am using Unity3D. Do I have to cast it myself? I have read about covariance and contravariance, but I couldn’t make sense of this one.

Answer 1

I’ve decided to change the dictionary to a more common one by using Delegate and also defining a normal EventFilter class without generics. I hope that the casting will be correct, since I haven’t tested this yet. I hope that it will work.

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<Delegate, EventFilter> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}