如何在 KMM（kotlin 本机）共享模块中读取 Swift 框架库中生成的对象数组

Question

I'm working on a KMM app. The shared module has a helper class, that relies on different native libraries for the android part and for the iOS part. This is implemented with the already know "expected/actual" pattern.

As said, the iOS actual class makes use of an iOS framework, that performs some calculations, and returns an array of objects. The ios framework that creates the list of objects works correctly (it was tested with unit tests). A simplified example follows below.

This is the class of the objects that are inside of the array:

public class ChildNodeIos:  NSObject{

public  let content:String
public let isTextNode:Bool

public init(content:String,isTextNode:Bool=false){
    self.content=content
    self.isTextNode=isTextNode
}

}

The helper class on the iOS side that returns the list of objects would be something like that:

@objc public class IOSCoolHelper: NSObject {
    @objc public func getChildNodes(message: String) -> [ChildNodeIos]  {
       //build the array of child nodes here and return them
     }
}

In the kotlin shared module, inside the iOS expected class, the function is called like the following:

@Serializable
data class ChildNodeKN(val content :String,val isTextNode :Boolean=false)

import com.mydomain.iosframeworks.IosCoolHelper
actual class CoolHelper actual constructor(private val someStuff: String)  : ICoolHelper {

       actual override fun getChildNodes(message: String): List<ChildNodeKN> {
            val iosHelper= IOSCoolHelper()
            val swiftarray:List<ChildNodeIos>  = iosHelper.getChildNodes(message)
    
            //I was expecting to do something like that but it does not work (the content of "array is always empty"):
    
            val kotlinList:List<ChildNodeKN> = swiftarray as List<ChildNodeIos>
    
         return kotlinList
    }
        }
    
    }

Or maybe if the list of swift objects can not be direct be casted to the equivalent kotlin object list, I was expecting to be able to iterate over the swift list and convert it to the kotlin list, something like that:

    val kotlinList=mutableListOf<ChildNodeKN>()
swiftArray.foreach{
kotlinList.add(ChildNodeKN(it.content,it.isTextNode))
}

But again, the content of the swift Array is empty. Doing a lot of tests (I can no reproduce them now), I managed to access something inside the array, but it was not an object of type ChildNodeIos, nor something I could read on the kotlin side.

Well, the question is, how to receive on the kotlin side, a list with more or less complex objects inside, that was generated on the iOS side?

I have to say, that this swift helper class has many other functions that return primitive values (strings, booleans, or int), and that is working very well.

I suppose a workaround would be instead an array with objects, to return an array with primitive types and two dimensions from the Swift side, but I would like to work with an array of objects if it is possible.

Thank you for your help

Answer 1

I managed to find the solution by myself. The problem was the declaration of the Swift class of the object contained in the list. I forgot the @objc declaration for the properties of the class, because if that I was not able to read the objects inside the returned array.

public class ChildNodeIos: NSObject{

@objc  public  let content:String
@objc  public let isTextNode:Bool

public init(content:String,isTextNode:Bool=false){
    self.content=content
    self.isTextNode=isTextNode
}

}

And then, on the Kotlin side, I did not achieve to cast it directly to a list, but with a foreach loop it is very easy to write the iOS objects in Kotlin objects: