How to define a callback in C

[cihadturhan]

Hi @jwtan,

Thank you for sharing this, I spent countless hours to fix Unity + Swift problem. Without your explanation I couldn't understand what are the problems. I wish I could've found this repo earlier.
I think you should share this on unity forums because this is a hidden gem here :)

So, I have a project that I want to integrate with a swift library but I can't use the callback on swift:

I create a header to define my callback

// SwiftToUnityBridge.h
#ifndef SwiftToUnityBridge_h
#define SwiftToUnityBridge_h

#ifdef __cplusplus // gives error without it
extern "C" {
#endif

 typedef void (*SwiftCallback)(); //<- I define the callback here

#ifdef __cplusplus
}
#endif

#endif

Then, add a callback on mm file

// SwiftToUnityBridge.mm
#import <UnityFramework/UnityFramework-Swift.h>

extern "C"
{
 void UnityOnStart()
 {
 [[SwiftToUnity shared] UnityOnStart];
 }

+ void CallWithACallback(SwiftCallback callback)
+ {
+ [[SwiftToUnity shared] callWithCallback: callback];
+ }
}

and, define a function on swift

// SwiftToUnity.swift
import Foundation

@objc public class SwiftToUnity: NSObject
{
 @objc public static let shared = SwiftToUnity()

 @objc public func UnityOnStart()
 {
 UnitySendMessage("Cube", "OnMessageReceived", "Hello World!");
 }
 
+ @objc public func call(callback: @escaping SwiftCallback)
+ {
+ callback();
+ }
}

And moved the header from project to public (I don't know if I should do this)

After that, I added the header to UnityFramework.modulemap

framework module UnityFramework {
 umbrella header "UnityFramework.h"

 export *
 module * { export * }

 module UnityInterface {
 header "UnityInterface.h"
+ header "SwiftToUnityBridge.h"

 export *
 }
}

But I can't find out why it still doesn't let me use the callback

Generated UnityFramework-Swift.h:

Thank you for sharing this.