Write Unity IOS plugin in Swift code

Question

Is it possible to write unity IOS plugin in Swift?

I already have a working swift framework and want to use it as a plugin in Unity

I saw some places which say it can only be done on Objective-c but is there a workaround for swift?

Answer 1

How to call Unity methods

Unity interface functions are defined in UnityInterface.h in Xcode project built by Unity. This header file is imported in UnitySwift-Bridging-Header.h, so you can call the functions directly in your Swift codes.

To call Unity methods, use UnitySendMessage function like below:

    //  Example.swift

import Foundation

class Example : NSObject {
    static func callUnityMethod(_ message: String) {
        // Call a method on a specified GameObject.
        UnitySendMessage("CallbackTarget", "OnCallFromSwift", message)
    }
}

How to access Swift classes from Unity

Step 1: Create your Swift classes.

//  Example.swift

import Foundation

class Example : NSObject {
    static func swiftMethod(_ message: String) {
        print("\(#function) is called with message: \(message)")
    }
}

Step 2: Include "unityswift-Swift.h" and define C functions to wrap Swift classes in .mm file (Objective-C++).

//  Example.mm

#import <Foundation/Foundation.h>
#import "unityswift-Swift.h"    // Required
                                // This header file is generated automatically when Xcode build runs.

extern "C" {
    void _ex_callSwiftMethod(const char *message) {
        // You can access Swift classes directly here.
        [Example swiftMethod:[NSString stringWithUTF8String:message]];
    }
}

Step 3: Create interface class to call exported C functions from C#.

// Example.cs

using System.Runtime.InteropServices;

public class Example {
    #if UNITY_IOS && !UNITY_EDITOR
    [DllImport("__Internal")]
    private static extern void _ex_callSwiftMethod(string message);
    #endif

    // Use this method to call Example.swiftMethod() in Example.swift
    // from other C# classes.
    public static void CallSwiftMethod(string message) {
        #if UNITY_IOS && !UNITY_EDITOR
        _ex_callSwiftMethod(message);
        #endif
    }
}

Step 4: Call the method from your C# code.

Example.CallSwiftMethod("Hello, Swift!");

The file names of UnitySwift-Bridging-Header.h and unityswift-Swift.h are defined in "Objective-C Bridging Header" entry and "Objective-C Generated Interface Header Name" entry in Build Settings. These settings and other settings about Swift compiler are set automatically by PostProcesser when the Unity build runs.

Requirements

iOS 7 or later

Compatibility

Unity 5.3.5f1 Xcode 7.3.1

Answer 2

As top-level Swift is simply not accessible from Unity, the "workaround" for Swift is to write an Objective-C wrapper class around it, and access that.

Depending on the amount and complexity of your Swift code that might still be the most optimal approach.