Question

The .net EventHandler is limited to Templates that inherits from EventArgs. How is that done? The implementation (Got to refference in vs) shows the following code:

[Serializable] public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e); 

But i think TEventArgs is just a name. How can I write a typed delegate that is limites to anything that inherits from MyClass?

Answer 1

TEventArgs is a generic type parameter – but it has a constraint. The actual signature is:

[Serializable] public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e)     where TEventArgs : EventArgs 

The ‘where TEventArgs : EventArgs‘ bit is the type constraint which means you can only supply a type argument for TEventArgs which is EventArgs or a derived class.

Basically it’s just ‘normal’ C# generics, just applied to a delegate declaration.