Event parameter; "sender as Object", or "sender as T"?

Question

When I write public events for my business objects, I've adapted the habit of always passing the instance as "sender as Object", in addition to additional specific parameters. I just asked myself now why am I not specifying the class?

So for you with more experience; Do you ever pass the distinct class as sender in an event? And if so, what are your decision criteria for when this is ok/not ok?

Answer 1

Don't be extreme. EventHandler(object sender, EventArgs e) has an object sender so that we can use it in many circumstances. But it doesn't mean a strongly-typed sender is evil. A strongly-typed sender is useful when this delegate is not going to be widely used(like EventHandler) e.g.

public delegate void SaveHandler(Controller sender, EventArgs e);

Now other developers(or someone using your library) can recogonize that the sender have to be a Controller, and they will be glad not to code like this:

public void MySaveHandler(object sender, EventArgs arg)
{
   var controller = sender as Controller;
   if (controller != null)
   {
       //do something
   }
   else
   {
       //throw an exception at runtime? 
       //It can be avoided if sender is strongly-typed
   }
}

And you can even make it generic:

public delegate void SaveHandler<T>(T sender, EventArgs args) 
                                              where T: IController;

It's pure legal and good practice in C#. You should make clear what you want to do, and then choose the better way. Either of them is evil/bad.