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Delegates

im having problems trying to understand the delegates in
c#, does anybody know some link where i can find a good
and simple explanation?

thanks
Nov 15 '05 #1
15 3703
kode,

Check out the section of the .NET framework documentation titled
"Delegates Tutorial", located at (watch for line wrap):

http://msdn.microsoft.com/library/de...estutorial.asp

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

"kode" <an*******@disc ussions.microso ft.com> wrote in message
news:00******** *************** *****@phx.gbl.. .
im having problems trying to understand the delegates in
c#, does anybody know some link where i can find a good
and simple explanation?

thanks

Nov 15 '05 #2
there's also a pretty good chapter in Jesse Liberty's C#
book, which just happens to be available FREE ONLINE
http://www.oreilly.com/catalog/progc...hapter/ch12.pd
f

cheers!

btw his discussion of why events have the accessors they
do is dumb, but that's another story..

-----Original Message-----
kode,

Check out the section of the .NET framework documentation titled"Delegates Tutorial", located at (watch for line wrap):

http://msdn.microsoft.com/library/default.asp? url=/library/en-us/csref/html/vcwlkdelegatest utorial.asp
Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

"kode" <an*******@disc ussions.microso ft.com> wrote in messagenews:00******* *************** ******@phx.gbl. ..
im having problems trying to understand the delegates in c#, does anybody know some link where i can find a good
and simple explanation?

thanks

.

Nov 15 '05 #3
would b hacker <al****@digital word.net> wrote:
btw his discussion of why events have the accessors they
do is dumb, but that's another story..


What's "dumb" about it? Makes perfect sense to me.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #4
the problem with the event model is that it offers an add-
remove syntax which prevents retrieving any delegates
that have been assigned to the event. this means that
you can't retrieve event handlers in reflection, for
instance you can't copy event handlers from one object to
another.

according to liberty, this is to prevent objects with
access to the event (Main in liberty's example) from
impersonating the event (Main causing the printing of a
fictitious time on the console). this kind of issue is
silly, of coures main can do all kinds of wierd stuff if
it really wants, requiring that main not hijack events
should be a matter of style not language grammar.

btw does anybody know if there is a pre-c# history to the
event model that c# simply copied, or is the add/remove
event model novel with c#?

-----Original Message-----
would b hacker <al****@digital word.net> wrote:
btw his discussion of why events have the accessors they do is dumb, but that's another story..


What's "dumb" about it? Makes perfect sense to me.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
.

Nov 15 '05 #5
The concern is more about accidental problems as opposed to malicious
intent. If you could assign directly, you'd be able to write:

appDomain.Domai nLoadEvent = new EventHandler(ro utine);

If somebody was already hooked up to the event, you would have just unhooked
them. Which would be bad.
--
Eric Gunnerson

Visit the C# product team at http://www.csharp.net
Eric's blog is at http://blogs.gotdotnet.com/ericgu/

This posting is provided "AS IS" with no warranties, and confers no rights.
"wood bee hacker" <al****@digital word.net> wrote in message
news:02******** *************** *****@phx.gbl.. .
the problem with the event model is that it offers an add-
remove syntax which prevents retrieving any delegates
that have been assigned to the event. this means that
you can't retrieve event handlers in reflection, for
instance you can't copy event handlers from one object to
another.

according to liberty, this is to prevent objects with
access to the event (Main in liberty's example) from
impersonating the event (Main causing the printing of a
fictitious time on the console). this kind of issue is
silly, of coures main can do all kinds of wierd stuff if
it really wants, requiring that main not hijack events
should be a matter of style not language grammar.

btw does anybody know if there is a pre-c# history to the
event model that c# simply copied, or is the add/remove
event model novel with c#?

-----Original Message-----
would b hacker <al****@digital word.net> wrote:
btw his discussion of why events have the accessors they do is dumb, but that's another story..


What's "dumb" about it? Makes perfect sense to me.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
.

Nov 15 '05 #6
wood bee hacker <al****@digital word.net> wrote:
the problem with the event model is that it offers an add-
remove syntax which prevents retrieving any delegates
that have been assigned to the event. this means that
you can't retrieve event handlers in reflection, for
instance you can't copy event handlers from one object to
another.
Which is good in many ways - if a class *wants* to expose which
handlers are being used, it can do so, but it doesn't *have* to.
according to liberty, this is to prevent objects with
access to the event (Main in liberty's example) from
impersonating the event (Main causing the printing of a
fictitious time on the console). this kind of issue is
silly, of coures main can do all kinds of wierd stuff if
it really wants, requiring that main not hijack events
should be a matter of style not language grammar.
No, because it helps to stop mistakes happening, just like strong
typing, access modifiers and the like. Would you suggest that
everything should be public as well? It's the same kind of argument.
btw does anybody know if there is a pre-c# history to the
event model that c# simply copied, or is the add/remove
event model novel with c#?


Don't know, to be honest.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #7
I can still app hijack with PostMessage and subclassing outside the runtime.
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...
wood bee hacker <al****@digital word.net> wrote:
the problem with the event model is that it offers an add-
remove syntax which prevents retrieving any delegates
that have been assigned to the event. this means that
you can't retrieve event handlers in reflection, for
instance you can't copy event handlers from one object to
another.


Which is good in many ways - if a class *wants* to expose which
handlers are being used, it can do so, but it doesn't *have* to.
according to liberty, this is to prevent objects with
access to the event (Main in liberty's example) from
impersonating the event (Main causing the printing of a
fictitious time on the console). this kind of issue is
silly, of coures main can do all kinds of wierd stuff if
it really wants, requiring that main not hijack events
should be a matter of style not language grammar.


No, because it helps to stop mistakes happening, just like strong
typing, access modifiers and the like. Would you suggest that
everything should be public as well? It's the same kind of argument.
btw does anybody know if there is a pre-c# history to the
event model that c# simply copied, or is the add/remove
event model novel with c#?


Don't know, to be honest.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #8
news.microsoft. com <an********@dis cussions.micros oft.com> wrote:
I can still app hijack with PostMessage and subclassing outside the runtime.


Sure. It's not absolutely preventing you from doing horrible thing -
but it's making life easier for those of us who don't *want* to do
nasty things, but would make mistakes if it were really easy to do
those things.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Nov 15 '05 #9
Its something .NET should have addressed. An unsecure app message queue.
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...
news.microsoft. com <an********@dis cussions.micros oft.com> wrote:
I can still app hijack with PostMessage and subclassing outside the
runtime.
Sure. It's not absolutely preventing you from doing horrible thing -
but it's making life easier for those of us who don't *want* to do
nasty things, but would make mistakes if it were really easy to do
those things.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

Nov 15 '05 #10

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