I have an iOS application that uses some shared co...

# kotlin-native

[gaetan]

I have an iOS application that uses some shared code that itself depends on a Kotlin multiplatform library.

iOS.app -> shared -> library

I’m trying to develop a timer that uses CADisplayLink in the Kotlin code. This is the code of my “timer”:

@ThreadLocal
object AppTimer {

   fun start(){
      val selector = NSSelectorFromString("execution")
      val displayLink = CADisplayLink.displayLinkWithTarget(this, selector)
      displayLink.addToRunLoop(NSRunLoop.currentRunLoop, NSRunLoop.currentRunLoop.currentMode)
   }

   @ObjCAction
   fun execution(){
      NSLog("AppTimer::Execution through CADisplayLink")
   }
}

It works without problem if the timer code is located in the shared module. But, when I move it into the library, it throws this error:

2021-10-27 13:45:35.769237+0200 iOSApp1[21754:6605253] -[App1_kobjcc0 execution]: unrecognized selector sent to instance 0x6000026025e0
2021-10-27 13:45:35.793415+0200 iOSApp1[21754:6605253] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[App1_kobjcc0 execution]: unrecognized selector sent to instance 0x6000026025e0'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff20422fba __exceptionPreprocess + 242
	1   libobjc.A.dylib                     0x00007fff20193ff5 objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff20431d2f +[NSObject(NSObject) instanceMethodSignatureForSelector:] + 0
	3   CoreFoundation                      0x00007fff204274cf ___forwarding___ + 1455
	4   CoreFoundation                      0x00007fff204297a8 _CF_forwarding_prep_0 + 120

Does anyone have an idea of why this is happening?

[gaetan]

Found my problem. I forgot to export the library in my cocoapod:

framework {
   baseName = "shared"
   export(project(":library"))
}

[louiscad]

There's a better solution to make Objective-C selectors work in your Kotlin projects without forcing extra config on consumers:
1. Make the target selector class extend NSObject (that'd be AppTimer class in your case).
2. Don't use object as they cannot extend NSObject (it currently fails the compilation of the consumers…), use class instead (you can put a shared instance in a top-level val).
3. Make sure the class is public (but its constructor doesn't have to be, internal is fine).
See example commit here: https://github.com/data2viz/data2viz/commit/9aa369fefb6c1c17ee71f6ae30356ffd15c4615f

Thanks @jw for helping me get there 🙂