Re: function pointer in Cocoa
Re: function pointer in Cocoa
- Subject: Re: function pointer in Cocoa
- From: Wade Tregaskis <email@hidden>
- Date: Fri, 4 Jun 2004 01:51:52 +1000
Is there anyone having experience using function pointer in Cocoa? I
am currently developing an application for my experiment using OSX's
CoreAudio. In particular, there is a function AudioDeviceStart, which
calls a C-type function pointer (*AudioDeviceIOProc). To utilize this
function, I create a class called "SoundCard" (I want fully control of
the soundcard, Revolution 7.1). The question I have is, how to handle
this function pointer? Can I declare it as the instance variable of
"SoundCard" class? If so, how and where to define the function? Since
the function needs to be implemented in C? I could make the program
working if I put the definition of the C-function in the SoundCard.m
file. However, it is really ugly. Any idea?
I'm no expert, but usually when you want a function callback to end up
going to an object, there's not much you can do but write a bridge
function for it.
Depending on what user-data you're allowed to setup for your callback,
you might be able to do something simple like pass a pointer to your
object as your user-data, so your bridge function need only call the
appropriate method on the instance it is given. It requires a bit of
care with regards to memory management while the callback is installed,
but in most cases any clean design will see those issues through quite
happily.
If you don't have that user-data luxury, then you might have some
trouble if you need more than one callback installed at a time. With
just one you can store the destination object in a global variable
(yes, gross, but it's functional) and be done with it... otherwise,
you'll need to figure out some alternate way to distinguish between
destination objects based on whatever information your callback has,
and store your destinations in a map (C++) or dictionary (ObjC), or
whatever else is appropriate.
Wade Tregaskis (aim: wadetregaskis)
-- Sed quis custodiet ipsos custodes?
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