Hello guys, I have a question: I want to compile my commonMain and iosMain kotlin code into a static library, I achieve this target with gradle plugin, but my problem is, I don't know how to implement an abstract kotlin class in Objective-C and pass it to kotlin, because when I compile kotlin code to static library, all stuff are C struct. Here is my kotlin abstract class:

abstract class ConfEvents {
  open fun onPeerJoined(uid: String) {}
}

Here is the generated C header:

struct {
  libAvConf_KType* (*_type)(void);
  libAvConf_kref_com_piasy_avconf_ConfEvents (*ConfEvents)();
  void (*onPeerJoined)(libAvConf_kref_com_piasy_avconf_ConfEvents thiz, const char* uid);     
} ConfEvents;

If I compile kotlin code into framework, then

ConfEvents

would have a Objective-C interface, then I can extend it and pass it to kotlin.

What I’m doing right now is building a wrapper around the C API

@Cristián Arenas Thanks for your reply, but I may not explain myself clearly, what I want to do is create a sub class of the kotlin

ConfEvents

class in Objective-C, and its method will be called at kotlin code, and I need pass that Objective-C object to a kotlin method which receive a

ConfEvents

object. That kotlin method is:

fun create(
      uid: String,
      events: ConfEvents
    ): AvConf

And the generated C API is:

libAvConf_kref_com_piasy_avconf_AvConf (*create)(libAvConf_kref_com_piasy_avconf_AvConf_Companion thiz, const char* uid,  libAvConf_kref_com_piasy_avconf_ConfEvents events);

In your description, it seems to wrap a kotlin object with an Objective-C object, and use it in Objective-C, am I right?

In your description, it seems to wrap a kotlin object with an Objective-C object, and use it in Objective-C, am I right?

Yes, that’s the idea. I do not yet know how to create an Objective-C header when creating a static library, so wrapping the C API in an Objective-C class would solve some of your problems. After wrapping all the methods, you can subclass that class in Objective-C, the only difference would be that if any function requires a pointer to the original

ConfEvents

class, you would have to pass it the inner private instance (of type

libAvConf_kref_com_piasy_avconf_ConfEvents

). The better solution would be to ask how to generate the static library with an Objective-C API, I have no idea how to do that

Sorry I still have doubt about your suggestion: if the

onPeerJoined

function of

ConfEvents

is called in kotlin code, how could the Objective-C code be called?

I’m not sure what you mean

Okay, let me explain it.

so wrapping the C API in an Objective-C class

You mean I can create an Objective-C class, e.g.

ObjCConfEvents

, it will own a pointer of

libAvConf_kref_com_piasy_avconf_ConfEvents

, and its

onPeerJoined

method will call

void (*onPeerJoined)(libAvConf_kref_com_piasy_avconf_ConfEvents thiz, const char* uid);

, then I can create subclass of

ObjCConfEvents

, e.g.

SpecialConfEvents

, and doing the real logic in its

onPeerJoined

method, right?

the only difference would be that if any function requires a pointer to the original

ConfEvents

class, you would have to pass it the inner private instance (of type

libAvConf_kref_com_piasy_avconf_ConfEvents

)

You mean I need pass the

libAvConf_kref_com_piasy_avconf_ConfEvents

of

ObjCConfEvents

to kotlin code (the

create

function), right? If my understanding is correct, when kotlin code call

onPeerJoined

of

libAvConf_kref_com_piasy_avconf_ConfEvents

, how could the

ObjCConfEvents

get called? Sorry if my understanding is wrong, and please correct me if so. Thank you very much!

ah

yeah I understand that

I would think that that is not possible using subclasses

okay, if so, then that's bad 😞 but fortunately we can compile kotlin code as framework, although the naming is out of our control, but we can create another wrapper framework over it.

I’m in the same boat as you

yeah, the gradle plugin doesn't have bitcode option when compiling static lib

that means I have to disable bitcode in the iOS app, which is not an option for me (used by external clients), so I can only make frameworks

I haven't use umbrella framework before, I haven't even hard about it, lol

umbrella framework = framework with frameworks inside, it’s what you suggested

oh, I didn't mean that, by saying wrapper framework, I mean another separate framework, which just contains classes that wrap API of the original framework's classes.

so you would need to install both on the iOS app?

yes, not perfect, but it works

well, if you go the wrapping framework route as I did: The way to fix this codesigning problem, is to add a Run Script build phase, where you can use the

codesign

command line tool.

f="$CODESIGNING_FOLDER_PATH/Frameworks/YourOuterFrameworkName.framework/Frameworks/YourInnerFrameworkName.framework"

codesign --force --sign "$EXPANDED_CODE_SIGN_IDENTITY_NAME" --preserve-metadata=identifier,entitlements --timestamp=none "$f"

That way the app project only needs to depend on the outer one

great! thanks for sharing

just in case you ever try that

😂

and if someone had said this 2 months ago, I would’ve never chosen kotlin as a way to share code

long way to go for kotlin mpp

If you figure anything else out, please share it with me 🙏

Sure I will

Just a word on static libs with bitcode - please try this approach(https://kotlinlang.slack.com/archives/C3SGXARS6/p1575971172220200?thread_ts=1575913985.211900&cid=C3SGXARS6), and tell if this is not working.