The approach I took for my wrapper library was using bindings. Not the Cocoa
type, but the language type. I created a series of Objective-C classes that
serve as the Obj-C interface to the Cocoa developer. The Obj-C classes would
make calls into the C/C++ libraries and do conversions between C/C++ types to
Obj-C. For example the C-string to NSString conversion. This way, a convenient
Objective-C framework could be created that Cocoa developers could use very
easily. C arrays were converted to Foundation NSArrays, etc. There was also
conversions of C++ exceptions to Obj-C exceptions, although this might be
unified in CLang/LLVM.
Since I was wrapping a C++ library, I made up some special bindings that
allowed me to call into C++ objects via templates and some special sauce that
allowed us to store method pointers and call into them from any
platform/language. This is probably more work than is needed though.
Anyways, I didn’t use delegates, notifications, etc. The easiest way to
integrate these wrappers into your app is to have a pure Objective-C interface
and do all work inside those, but probably the most effort to write.
Doug Hill
> On Mar 4, 2016, at 1:14 PM, Alex Zavatone <z...@mac.com> wrote:
>
> Great! It certainly does… but here's where my brain breaks.
>
> The call is originating from the C lib and within the C function. I am not
> calling the C function from Objective-C.
>
> I'm looking at somehow passing this as a string (UTF-8, yep) back to an OC
> class instance, so this implies either a callback or some reference to the OC
> instance that that cares about the response and a means to get that message
> to it.
>
> If this is as simple as setting up a callback or a pointer reference, from
> the c class to the OC instance? Is it sane programming for the C class to
> have more than one callback to different OC object instances?
>
> I was thinking one for data and one for method calls for organizational
> purposes.
>
> Or should there be one layer that serves as a clearly defined API to create a
> walled garden between the OC world and the C interface to the compiled C lib?
>
>
> I'm working with PJSIP and PJ's docs clearly state, "we are going to crater
> unless you do everything SIP related on the main thread." The code that I am
> rewriting replacing has nasty try/catch clauses and forces many operations to
> the main thread just in case they call PJSIP operations - which clearly makes
> for a sucky user experience and really clunky application architecture.
>
> I'm looking to avoid that nastiness by starting from ground zero so that we
> can wrap a solidly conceived architecture around a neatly walled off
> interface layer to PJSIP.
>
>
> Would it make sense to send a notification from the C method to an
> Objective-C object to get the value from the C class? Then I'd need to worry
> about storing it, that seems clunky and too involved just to return a string.
>
> Thank you, sir. Loads for me to learn here.
>
> Alex Zavatone
>
>
>
> On Mar 4, 2016, at 3:48 PM, Doug Hill wrote:
>
>> Alex,
>>
>> I’ve worked on a few wrapper libraries, so I have some experience with this.
>>
>> In your Obj-C wrapper, you would need to create the NSString yourself. So,
>> if you have a C function:
>>
>> char* MyCFunc(void);
>>
>> The Objective-C wrapper method would do something like:
>>
>> - (void) myObjcMethod
>> {
>> char* cStr = MyCFunc();
>> NSString* objcStr = [[NSString alloc] initWithUTF8String:cStr];
>>
>> return objCStr;
>> }
>>
>> Depending on the C function implementation, you might have to deal with
>> releasing the C string in your wrapper. Also, I assume UTF-8 encoding, which
>> may or may not be true.
>>
>> Hopefully this helps you.
>>
>> Doug Hill
>>
>>
>>> On Mar 4, 2016, at 12:07 PM, Alex Zavatone <z...@mac.com> wrote:
>>>
>>> I'm in the middle of some fun where there is a wrapper class to a lib
>>> that's written in C and the c function has a char string that I'd like to
>>> return back to or somehow pass on to an Cbjective-C class.
>>>
>>> I'm sure there is an established practice for performing this type of task,
>>> but while I have the opportunity to do this, I'd like to start be learning
>>> the right way to handle this operation.
>>>
>>> I've seen really poor use of a catch all delegate for this approach, but am
>>> pretty unsure on viable and safe methods to handle this.
>>>
>>> Any tips to how to handle this?
>>>
>>> Thanks in advance,
>>>
>>> Alex Zavatone
>>
>>
>
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