How To Implement Swift and Objective-C cross compatibility with Unity in xCode

This repository is a note of how to implement cross compatibility between Swift and Objective-C within a Unity project in xCode.

Written with StackEdit.

Straight to the point

In order for your Swift code to call and access Objective-C variables and functions, and visavercer - Obj-c to call Swift functions and variables - we need to do a few steps

Swift calling Objective-C

in order to expose your Objective-C code to your Swift code you need to add your header files to the UnityFramework umbrella header (UnityFramework.h)

1 - add your .h files to the umbrella .h Find the umbrella file UnityFramework.h

Side note: UnityFramework.h is a UMBRELLA file for the framework (a file that contains all .h files, so you can just import UnityFramework.h and like not 54 single .h files..) https://www.google.com/search?q=xcode+what+is+a+umbrella+header

It is located at Unity-iPhone/UnityFramework/UnityFramework.h

Here we need to add our Objective-C headers that swift wants to see

For my use case, my 1 swift (UnityNativeSwift.swift) file needs to see my 1 objective-c file (UnityNativeObjC.mm)

Therefor we only need to add the UnityNativeObjC.h to UnityFramework.h, in order to expose UnityNativeObjC functionality to our Swift files

Open UnityFramework.h, find the line #import "UnityAppController.h" and add #import "UnityNativeObjC.h" above it

2 - add .h files to Public Headers setting

Now we need to add UnityNativeObjC.h as a public header

If it is not a public header, then Swift won’t be able to see it

Go to the project settings page (on the file hierarchy browser on the left, scroll to the top and click on Unity-iPhone at the top)

Select the UnityFramework target

Click on Build Phases (in the top right quadrant)

Expand Headers

The Public Headers list is where we want to drag and drop our .h that we want to expose to Swift

So, Drag and drop your objective-c .h file/s to the Public Headers list

Drag it to the top of the list (supposedly the order does matter. I do not know details and it just works at the top so put your .h file/s at the top of the public headers list)

Your Swift file/s should now see your Objective-C functionalities

Objective-C calling Swift

in order to expose your Swift code to your Objective-C code, your need to complete a successful build in order have xcode automatically generate the UnityFramework-Swift.h interface file for us.

1 - add .m/.mm to precompile

We need to add our Objective-C file and Swift file into the precompile list, in Build Phases, on the target UnityFramework

2 - do a successful build

We need to do a SUCCESSFUL build in order to auto generate the interface file UnityFramework-Swift.h

UnityFramework-Swift.h is a objective C file that has wrapper/helper methods that just point to the corresponding Swift class, var or function

We need this file to be auto generated so that we can reference it in our .m/.mm files, and expose the swift vars and funcs in our objective-c code

This file is autogenerated on a SUCCESSFUL build.

So comment out any code that is throwing out errors (if any) so that you can do a successful build

If you comment out functions this can cause other errors e.g “method does not exist”. So it might be easiest to just comment out the method’s body (the functions code) and not the actual functions

Now do a build with CMD-B, and hopefully it built successfully

3 - import auto generated interface

Now that the project has successfully been built, we can import the auto generated swift interface file UnityFramework-Swift.h

Open your objective-c .m/.mm file and add
#import <UnityFramework/UnityFramework-Swift.h>

your .m/.mm file should now see your swift code

NOTES:

• Make sure that all the Swift code you want your Objective-C code to see is marked with @objc and public

More insights and extra information

Bridging-Header in the past, the bridging-header method was used to in order to expose Swift and Objective-C cross functionatlity. But things changed. Sometime between 2018-2020 Unity or xCode changed something. (completely guessing this) The change meant that UnityFramework now handles the swift and objective-c files Here is the catch: frameworks CAN NOT USE bridging headers. therefor, new methods were necessary.

the new methods:

1. Umbrella header for Swift calling obj-c
2. Auto generated interface file for Obj-c calling Swift

Links:

• https://stackoverflow.com/questions/24002369/how-do-i-call-objective-c-code-from-swift/59217109#59217109

  • Scroll down to Mixing Objective-C and Swift.
  • This is exactly what we are trying to achieve

• https://forum.unity.com/threads/swift-ios-native-plugins-hurdles.802623/

• Shopify/unity-buy-sdk#596 scroll to the bottom

• https://forum.unity.com/threads/build-ios-umbrella-error.838879/?_ga=2.251789065.1455154538.1587560504-695413727.1537284823#post-5660662

Code example

Swift

				UnityNativeSwift.swift

import Foundation
@objc  public  class  UnityNativeSwift : NSObject
{

    //Global static instance
    @objc  public  static  var  _sharedInstance = MySwift();

 
    //Variables
    var  aString = ""
    public var byteArray : [UInt8] = []

    @objc public func exampleSimpleMethod(arg1:String, arg2:String)
    {
	    // ... do stuff
	    let unityNativeObjC: UnityNativeObjC = UnityNativeObjC()
		unityNativeObjC.exampleObjCMethod();
		aString = unityNativeObjC.someVariable;
    }

    @objc public func exampleComplexMethod(arg1:String, arg2:String)
    {
	    aString = arg1;
    }

}

Objective-C

				UnityNativeObjC.h
#import <Foundation/Foundation.h>
@interface  MyObjC : NSObject

@property (strong, nonatomic) id  exampleVar;

- (**void**) exampleObjCMethod;

@end



				UnityNativeObjC.m
#import "UnityNativeObjC.h"
#import <AVFoundation/AVFoundation.h>

@implementation  UnityNativeObjC

- (void) exampleObjCMethod 
{
    NSLog(@"Hello World");
}
@end

SEO key words: How to use Objective-C code in Swift with Unity in xCode How to use Swift code in Objective-C with Unity in xCode Swift and Objective-C cross compatibility in a Unity project with Native plugins