Why Is the sender type null when dealing with events
- by ChloeRadshaw
From C# Via CLR:
Note A lot of people wonder why the event pattern requires the sender parameter to always
be of type Object After all, since the MailManager will be the only type raising an event with a
NewMail EventArgs object, it makes more sense for the callback method to be prototyped like
this:
void MethodName(Mai l Manager sender, NewMail EventArgs e);
The pattern requires the sender parameter to be of type Object mostly because of inheritance
What if Mai lManager were used as a base class for SmtpMailManager? In this case, the callback
method should have the sender parameter prototyped as SmtpMailManager instead of
Mail Manager, but this can’t happen because SmtpMai lManager just inherited the NewMai l
event So the code that was expecting SmtpMail Manager to raise the event must still have to
cast the sender argument to SmtpMailManager In other words, the cast is still required, so the
sender parameter might as well be typed as Obj ect
The next reason for typing the sender parameter as Obj ect is just fexibility It allows the delegate to be used by multiple types that offer an event that passes a NewMail EventArgs object
For example, a PopMai lManager class could use the delegate even if this class were not derived
from Mail Manager
I just simply cannot understand why the sender is an object - Why can it not be generified? so most of the time we do not need to do generic casts
