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Create an iOS Native Plugin for Unity using Swift

  • Unity Native Plugin allows your game to embed features of the OS that are not provided by default.
  • You can integrate Bluetooth, MP4 video creation, and more into your game.
  • Use the Swift Package Manager to make the framework and embed it in Unity.
  • Benefits of Making Framework
    • Configuration is completed in Unity's Inspector.
    • You can use Swift app targets to check the working of your plugins.
      • No need to build unity to check the working.

About Example

  • Implement a Native Plugin that converts a number of type string to type long.
  • The function swiftPmPlugin_toNumber defined with [DllImport("__Internal")] is the target function.
  • This function also exists in C#, but you can use the iOS function in the same way.
public class Cube : MonoBehaviour
{
    // target function
    [DllImport("__Internal")]
    private static extern long swiftPmPlugin_toNumber(string numberString);

    void Update()
    {
        // calling
        Debug.Log("number is: " + swiftPmPlugin_toNumber("30"));
    }
}

Implement the Native Plugin

  • Implement using the Swift Package Manager and output the Framework
  • Make a SwiftPmPlugin.framework that implements swiftPmPlugin_toNumber.

Environment

  • maxOS 11.3.1
  • Xcode 12.5
  • Swift 5.4.0
  • Unity 2020.3.5f1

Swift Package Manager

  • Initialize the package with type=library and package name.
  • Open Package.swift.
  • Xcode will launch, edit SwiftPmPlugin.swift.
swift package init --type=library --name=SwiftPmPlugin
open Package.swift

Implement SwiftPmPlugin.swift

  • Implement the logic in Swift.
  • Create a toNumber function in the SwiftPmPlugin class to convert a string to a number.
class SwiftPmPlugin {
    var text = "Hello, World!"
    static func toNumber(string: String) -> Int {
        return Int(string) ?? 0
    }
}

Make a function called in C#.

  • Make a function attributed to @_cdecl.
  • Convert the char array argument to Swift's String type.
  • Get an Int value from a string using SwiftPmPlugin.toNumber.
  • Convert the return value to Int64, because C# expects long type.
@_cdecl("swiftPmPlugin_toNumber")
public func swiftPmPlugin_toNumber(_ stringPtr: UnsafePointer<CChar>?) -> Int64 {
    let str = String(cString: stringPtr!)
    return Int64(SwiftPmPlugin.toNumber(string: str))
}

Build the Framework

  • Generate xcodeproj from SwiftPM.
  • Build the framework from xcodeproj using xcodebuild.
  • SwiftPmPlugin.framework is created in the directory you specified.
swift package generate-xcodeproj --skip-extra-files
xcodebuild -project SwiftPmPlugin.xcodeproj -scheme SwiftPmPlugin-Package -configuration Release -sdk iphoneos CONFIGURATION_BUILD_DIR=.

Build in Unity

Configure the Framework

unity_inspector_embed

Build an iOS app

  • Build the app for iOS in Unity and run it.

  • If it doesn't work, check the following

    • Unity-iPhone > General > Frameworks, Libraries, and Embedded Content.
    • SwiftPmPlugin.framework exists and is set to Embed & Sign.
    • If it's incomplete, you can add it manually and set it to.

    check_embed

Create a Native app target for Framework development.

  • Not required for Unity Native Plugin.
  • This is just a tip to make Framework development more convenient.
  • It's hard to go through the cycle of Framework build -> Unity build -> iOS to check if plugins works.
  • So I think it's more effective to make an app target and develop plugins.

Create xcworkspace

  • Create the SwiftPmPlugin.xcworkspace.

  • Import the Package.

  • Create an app target.

  • The language can be either Objective-C or Swift.

  • Add SwiftPmPlugin to the "Frameworks, Libraries, and Embedded Content" section of your app target.

  • Calling from Objective-C

#import "ViewController.h"
@import SwiftPmPlugin;
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    NSLog(@"value: %lld", swiftPmPlugin_toNumber("20"));
}
@end
  • Calling from Swift
import SwiftUI
import SwiftPmPlugin

struct ContentView: View {
    var body: some View {
        Text("number: \(swiftPmPlugin_toNumber("20"))")
            .padding()
    }
}

Conclusion

  • Implemented in Swift, managed by SwiftPM, and tested in a Native app for efficient development.