Re: NSInvocation question

FROM : Chris Suter
DATE : Sat Feb 23 02:47:22 2008

On 23/02/2008, at 2:36 AM, Hank Heijink wrote:

> The nice thing about NSInvocation is not so much its efficiency (or 
> lack thereof, as the case may be), but the fact that once you've got 
> the thing constructed, you can just call invoke on it, without 
> having to think about what's inside. I have functions of zero, one, 
> or two arguments that I wrapped up in NSInvocations. With IMPs, I 
> have to check the number of arguments both for the typing and for 
> the call.
>
> However, even with the check for number of arguments, an IMP is very 
> very fast.


What you say here doesn't make sense to me. Without knowing exactly 
what you're trying to do, it's difficult for me to comment. You can 
arrange things so that it's simple without using NSInvocations. It 
sounds like you've got some kind of delegate pattern, so the usual 
Cocoa way of doing this is to pass a selector and a target around. For 
example:

- (void)myCallBack1
{
  /* You can call another method here with whatever arguments you 
want. The arguments
      would be stored as instance variables of the object. */
}

- (void)myCallBack2
{
  // Likewise, you can call another method here with whatever 
arguments you want
}

- (void)myCallBack3
{
  // Do something
}

Elsewhere you'd have something like:

[myObject doSomethingWithDelegate:target selector:@selector 
(myCallBack1)];

Then to make the callback you'd simply do:

[target performSelector:selector];

If you want to speed things up, you'd get and cache the IMP. That's 
about as simple as doing [NSInvocation invoke] and there's no need to 
be doing any checking of number of arguments.

Kind regards,

Chris