Can I pass a function `(UIBackgroundFetchResult) -> void` from swift to Kotlin? Currently the met...

# multiplatform

[Aditya Kurkure]

Can I pass a function (UIBackgroundFetchResult) -> void from swift to Kotlin?
Currently the method I have written in kotlin expects a (UIKUIBackgroundFetchResult) -> void when called from swift.

[Sebastien Leclerc Lavallee]

I did a quick test, and yes you can do that. I had a function like:

fun doSomething(with: String, completion: (Time) -> Void) { }

And it was callable from Swift code without problem

[Aditya Kurkure]

Thanks. I still have the problem of swift expecting a UIKUIBackgroundFetchResult instead of UIBackGroundFetchResult though.

[Sebastien Leclerc Lavallee]

Oh I see… sorry I didn’t understand the question 😅 My bad.

So on the Swift side it’s called UIBackgroundFetchResult but KMM translate it to UIKUIBackgroundFetchResult 🤔 Hum… considering they are basically the same but with different names, I would cast the UIKUI version to UI. But this would need to be done on the Swift side.

[Aditya Kurkure]

Just tried this. Unfortunately it doesn't work.

[Adrian Witaszak]

Got the same issue. Did you get that sorted @Aditya Kurkure? I ended up returning result back to swift and handling it there, but that is not a perfect solution.

IOSFileKt.awaitResult { result in
            if result.isFailure {
                completionHandler(.failed)
            } else {
                completionHandler(.newData)
            }
        }

[Aditya Kurkure]

Yeah I did something similar. Haven't been able to find any other workaround.

[Darron Schall]

I was running into this same issue and stumbled upon this thread via search.

Here's what I have in iosMain :

fun kotlinMethodReturningUIBackgroundFetchResult(): UIBackgroundFetchResult {
  // Do some work, then return something like:
  return UIBackgroundFetchResult.UIBackgroundFetchResultNewData
}

Here's how I handle this in Swift:

// Even though the kotlin method returns `UIBackgroundFetchResult`
// it gets translated to `UIKUIBackgroundFetchResult`
// when exported to ObjC
let uikUIBackgroundFetchResult = kotlinMethodReturningUIBackgroundFetchResult()

// Convert the `UIKUIBackgroundFetchResult` back to the expected `UIBackgroundFetchResult` type
let rawValue = UInt(uikUIBackgroundFetchResult.value)
let backgroundFetchResult = UIBackgroundFetchResult(rawValue: rawValue)

Not ideal, but keeps the conversation back to UIBackgroundFetchResult on the Swift side relatively straightforward.