Delegates - A Real Practical Example

[sde]

I've been rackin my brain over delegates the last day. I have figured out in a sense HOW to use them, but I don't understand why.

Why can't we just call the class directly? I need a real world example of why we use delegates ( besides an event example )

Anyone?

[ender]

Here is my two bits to your question. Delegates (as I understand them) are just a typesafe way of passing pointers to member-functions/or functions in a type-safe way. Previously (in C++ and such) we just had a memory address, and we could call it with anything, which might not be what the function wants. Also, it doesn't hold any state information about the function. Delegates make it a type-safe way to call member functions.

A real world example besides an event handler would be anywhere you have used pointers to functions. For instance, I used them in a MUD I did for CS290 to handle how certain commands are processed. (Not 'events' but probably more like it than you wanted). For instance, someone typed "GO WEST" and I passed WEST to the function that was pointed to by the map of strings to functions. In this case, the function 'GO'. However, because of the uniformity of the arguments (I didn't pass any integers or anything) there wasn't any problems making sure there were sufficient arguments or types the the function because it was all standardized.

Another example of where you would use these are for dynamic validation of data. For instance, someone passes you a phone number, and depending on where you are located, or selected country, you can customize the function that will handle that phone number to validate it.

This is what I think, if I am wrong about what delegates are, please ignore/correct my post!

Hope this helps,
Ted Morse

[sde]

thanks ender. the go west example helps .. i think i just need to get stuck in one of my programs where i have no other choice but to use a delegate.

i even got delegates working between forms, basically just one form referencing a method in another form, .. but i had to pass the delegate from one form to the other.

i thought, why not just pass the form from itself to the other.

still confused, but a little less.

[sdeming]

Check this: http://www.c2.com/cgi/wiki?ObserverPattern

Delegates are similar to Java listeners, but they more closely resemble the SubscriberNotify or Observer pattern in purity. Where java listeners are objects forced to implement the specified interface, delegates are mere functions with a fixed signature.

I can't think of a better way to describe their value, but mostly delegates are just nice for code clarity and cleanliness. Similar implementations in other languages are usually pretty ugly in comparison and the code isn't quite as obvious in its purpose.

[dubsonic]

hey sdeming, what's the deal with the hex in your signature.

just curious