Re: Implementing delegation

FROM : Joakim Danielson
DATE : Fri Nov 19 23:56:49 2004

Hi

This is not a direct answer to your question but there is a good 
article at Cocoa Dev Central about this, 
http://www.cocoadevcentral.com/articles/000075.php

Joakim

On 2004-11-19, at 20.51, Bruce Toback wrote:

> Hi all,
>
> Is there some developer information somewhere on the best way to 
> implement delegation in my own frameworks?
>
> Currently, when one of my objects with a delegate intends to call a 
> delegate method, it does something like this:
>
>    if ([delegate 
> respondsToSelector:@selector(myObject:wantsToTellYou:)])
>      [delegate myObject: self wantsToTellYou: something];
>
> There are three things that seem to be wrong with this:
>
> 1. I'm testing to see if the delegate implements a method on every
>    message to the delegate. Obviously, I could cache the results of
>    the test the first time through. Is that worth the effort for
>    methods that aren't called in tight loops or something?
>
> 2. Because delegate is declared as id in my object, I get a compiler
>    warning on every delegate call. This is annoying.
>
> 3. Although it hasn't come up yet, the compiler assumes that the
>    return type of the delegate method is id. That may not always
>    be the case (and isn't now, but all delegate methods I've
>    defined up to now return void).
>
> To get around 2 and 3, should I just declare a protocol, and then 
> declare the delegate as a pointer to an object implementing that 
> protocol -- even though the protocol is informal? Is there any 
> downside to that? Or is there a widely-accepted set of idioms used to 
> implement delegation, and I'm just missing them?
>
> -- Bruce
>
> -----------------------------------------------------------------------
> -
> Bruce Toback      (602) 996-8601| My candle burns at both ends;
> OPT, Inc.          (800) 858-4507| It will not last the night;
> 11801 N. Tatum Blvd. Ste. 142    | But ah, my foes, and oh, my friends 
> -
> Phoenix AZ 85028                | It gives a lovely light.
> <email_removed>                |    -- Edna St. Vincent Millay
>
> _______________________________________________
> MacOSX-dev mailing list
> <email_removed>
> http://www.omnigroup.com/mailman/listinfo/macosx-dev
>