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Alternative Ways To Implement "Events"

Just looking to compile a list of "all the ways to implement events".

I'm NOT looking to get into the merits or mechanics of each in this
thread... just want to identify them all - good, bad, and ugly.

Here's what I have so far
1. Implement via the 'event' keyword (with associated delegate, etc)

2. Expose a private delegate via a public property (really a "roll yer own"
version of the 'event' keyword method).

3. Old-school callbacks in which one object (objA) calls another (objB),
passing a reference of itself to the called object (objB then contains a
reference to objA). The called object can then call methods on the calling
object (i.e., objB calls methods of objA).

4 ... ???

I'd appreciate any additional ways to implement "events" - including total
hacks.

I'm looking to grasp finally grasp the entire landscape of events and
callback mechanisms that are available in .NET (even if they are independent
of .NET, like plain ole' callbacks).

Thanks.
Aug 9 '07 #1
6 4772
Smithers,

Technically, you have to use the "event" keyword when you want to have
an event on your type. This is baked into the metadata (and shown through
Reflection) as an event. All the methods, besides #1, are not events,
technically.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Smithers" <A@B.comwrote in message
news:uh**************@TK2MSFTNGP03.phx.gbl...
Just looking to compile a list of "all the ways to implement events".

I'm NOT looking to get into the merits or mechanics of each in this
thread... just want to identify them all - good, bad, and ugly.

Here's what I have so far
1. Implement via the 'event' keyword (with associated delegate, etc)

2. Expose a private delegate via a public property (really a "roll yer
own" version of the 'event' keyword method).

3. Old-school callbacks in which one object (objA) calls another (objB),
passing a reference of itself to the called object (objB then contains a
reference to objA). The called object can then call methods on the calling
object (i.e., objB calls methods of objA).

4 ... ???

I'd appreciate any additional ways to implement "events" - including total
hacks.

I'm looking to grasp finally grasp the entire landscape of events and
callback mechanisms that are available in .NET (even if they are
independent of .NET, like plain ole' callbacks).

Thanks.

Aug 9 '07 #2

In some places .NET uses attributes to subscribe event handlers. Look
at OnSerializingAttribute and related attributes (there's 4 of them).

Java (at least as of 1.4, not sure if it changed), implements events
using interfaces. Instead of declaring an event like in C# each event
type has an interface and there are methods for subsribing to an
"event" by providing an interface implementation. Then inner classes,
especially anonymous inner classes, are heavily used as "event"
handlers. I probably have some details wrong but I'm pretty sure on
the basic principle.

DOM (JavaScript, ActionScript) implements events using name events and
function references (delegates). I've actually seen people implement
custom events in .NET this way, but in that situation we turned down
the contract because of that odd requirement.
And to be perfectly clear, I'm not advocating or condoning the use of
any of these methods over the standard way to create events in .NET..
just you asked for everything. :-)

HTH,

Sam
------------------------------------------------------------
We're hiring! B-Line Medical is seeking .NET
Developers for exciting positions in medical product
development in MD/DC. Work with a variety of technologies
in a relaxed team environment. See ads on Dice.com.

On Thu, 9 Aug 2007 13:26:09 -0700, "Smithers" <A@B.comwrote:
>Just looking to compile a list of "all the ways to implement events".

I'm NOT looking to get into the merits or mechanics of each in this
thread... just want to identify them all - good, bad, and ugly.

Here's what I have so far
1. Implement via the 'event' keyword (with associated delegate, etc)

2. Expose a private delegate via a public property (really a "roll yer own"
version of the 'event' keyword method).

3. Old-school callbacks in which one object (objA) calls another (objB),
passing a reference of itself to the called object (objB then contains a
reference to objA). The called object can then call methods on the calling
object (i.e., objB calls methods of objA).

4 ... ???

I'd appreciate any additional ways to implement "events" - including total
hacks.

I'm looking to grasp finally grasp the entire landscape of events and
callback mechanisms that are available in .NET (even if they are independent
of .NET, like plain ole' callbacks).

Thanks.
Aug 9 '07 #3
<snip>

<< While loosely, it is an event, the serialization engine uses reflection
to call the method >>>

<snip>

Nicholas,

Please note that the answer that Samuel provided is *exactly* the sort of
response I was looking for in my OP.

Please note that the OP subject has the word, events, in quotes ("events")
which indicates that I'm looking not only for events, but also anything that
can be roughly construed as an event. I went on in the body of the OP to
continue the use of quotes, and even explicitly requiested "total hacks"
(meaning not prim and proper events).

Please do not discourage folks from responding simply because they aren't
providing some way to implement events according to some narrow technically
specific definition. If thats' what I wanted, the OP wouldn't have described
my intent as going after the "entire landscape" of events and callback
mechanisms.... even those that are independent of .NET."

-S
Aug 9 '07 #4
Samuel,

The OnSerializingAttribute does not subscribe the method to an event.
While loosely, it is an event, the serialization engine uses reflection to
call the method.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Samuel R. Neff" <sa********@nomail.comwrote in message
news:sp********************************@4ax.com...
>
In some places .NET uses attributes to subscribe event handlers. Look
at OnSerializingAttribute and related attributes (there's 4 of them).

Java (at least as of 1.4, not sure if it changed), implements events
using interfaces. Instead of declaring an event like in C# each event
type has an interface and there are methods for subsribing to an
"event" by providing an interface implementation. Then inner classes,
especially anonymous inner classes, are heavily used as "event"
handlers. I probably have some details wrong but I'm pretty sure on
the basic principle.

DOM (JavaScript, ActionScript) implements events using name events and
function references (delegates). I've actually seen people implement
custom events in .NET this way, but in that situation we turned down
the contract because of that odd requirement.
And to be perfectly clear, I'm not advocating or condoning the use of
any of these methods over the standard way to create events in .NET..
just you asked for everything. :-)

HTH,

Sam
------------------------------------------------------------
We're hiring! B-Line Medical is seeking .NET
Developers for exciting positions in medical product
development in MD/DC. Work with a variety of technologies
in a relaxed team environment. See ads on Dice.com.

On Thu, 9 Aug 2007 13:26:09 -0700, "Smithers" <A@B.comwrote:
>>Just looking to compile a list of "all the ways to implement events".

I'm NOT looking to get into the merits or mechanics of each in this
thread... just want to identify them all - good, bad, and ugly.

Here's what I have so far
1. Implement via the 'event' keyword (with associated delegate, etc)

2. Expose a private delegate via a public property (really a "roll yer
own"
version of the 'event' keyword method).

3. Old-school callbacks in which one object (objA) calls another (objB),
passing a reference of itself to the called object (objB then contains a
reference to objA). The called object can then call methods on the calling
object (i.e., objB calls methods of objA).

4 ... ???

I'd appreciate any additional ways to implement "events" - including total
hacks.

I'm looking to grasp finally grasp the entire landscape of events and
callback mechanisms that are available in .NET (even if they are
independent
of .NET, like plain ole' callbacks).

Thanks.

Aug 9 '07 #5
I'm not trying to discourage people from answering, but I don't want to
spread the wrong impression about what an event is in .NET. It has a very
concrete definition (reflected by the metadata reflected on the type, and
reflected through the EventInfo type in the System.Reflection namespace).

To be frank, the question that you asked has a vast number of answers.
You are basically looking for anything that can signal your code in response
to an action. The number of mechanisms for this is pretty huge.

Some are more common than others, granted, and I feel you have hit on
all of the common ones, I believe, but there are many more to be had
(depending on the scenario and context).

--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com
"Smithers" <A@B.comwrote in message
news:OR**************@TK2MSFTNGP04.phx.gbl...
<snip>

<< While loosely, it is an event, the serialization engine uses reflection
to call the method >>>

<snip>

Nicholas,

Please note that the answer that Samuel provided is *exactly* the sort of
response I was looking for in my OP.

Please note that the OP subject has the word, events, in quotes ("events")
which indicates that I'm looking not only for events, but also anything
that can be roughly construed as an event. I went on in the body of the OP
to continue the use of quotes, and even explicitly requiested "total
hacks" (meaning not prim and proper events).

Please do not discourage folks from responding simply because they aren't
providing some way to implement events according to some narrow
technically specific definition. If thats' what I wanted, the OP wouldn't
have described my intent as going after the "entire landscape" of events
and callback mechanisms.... even those that are independent of .NET."

-S
Aug 10 '07 #6

And since I guess you missed this part of my original post, I'll
repeat..

"
And to be perfectly clear, I'm not advocating or condoning the use of
any of these methods over the standard way to create events in .NET..
just you asked for everything. :-)
"

While this may seem like a silly question, silly questions come up a
lot (especially in consulting contracts, which I'm glad we no longer
have to deal with) and it's always good to be knowledgeable about the
subject and know lots of ways to do things, even if you'd never
actually use them 'cause there is an accepted best practice (and of
course best practices do change over time, for example events are
different in plain .NET and WPF--although WPF events are based and a
wrapper of .NET events).

btw, Smithers, that's another one to add to your list. WPF supports
tunneling and bubbling of events. I'm not the most qualified to
explain it, but it's a very nice extension to .NET events.

Sam

------------------------------------------------------------
We're hiring! B-Line Medical is seeking .NET
Developers for exciting positions in medical product
development in MD/DC. Work with a variety of technologies
in a relaxed team environment. See ads on Dice.com.

On Thu, 9 Aug 2007 21:40:58 -0400, "Nicholas Paldino [.NET/C# MVP]"
<mv*@spam.guard.caspershouse.comwrote:
I'm not trying to discourage people from answering, but I don't want to
spread the wrong impression about what an event is in .NET. It has a very
concrete definition (reflected by the metadata reflected on the type, and
reflected through the EventInfo type in the System.Reflection namespace).

To be frank, the question that you asked has a vast number of answers.
You are basically looking for anything that can signal your code in response
to an action. The number of mechanisms for this is pretty huge.

Some are more common than others, granted, and I feel you have hit on
all of the common ones, I believe, but there are many more to be had
(depending on the scenario and context).
Aug 10 '07 #7

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