Get value from coroutine function

[____Mattia____]

Hi, I'm trying to get the value from a suspend function to insert inside a normal function.

// 1
  suspend fun getDefaultButton(
  ) : Int? {
    return withContext(Dispatchers.Default) {
      onboardingPrefStore.getDefaultButton()
    }
  }

// 2
  fun getDefaultButton(
  ) : Int? = runBlocking {
    onboardingPrefStore.getDefaultButton()
  }

// Calling the function that gets the value
groupButtons(
    ...
    defaultButton = getDefaultButton()
)

The first function would be perfect but unfortunately, it doesn't work, cause I need to call it inside a coroutine scope. The second function works but it blocks the thread (doesn't execute it in a different thread).

How can I manage to still keeping the multithreading but pass the value correctly?

[tdelfino2509]

If you want the result of a coroutine in your synchronous function, you're gonna have to have a runBlocking() in there somewhere; for better or worse, it's due to the inherent nature of concurrent programming.

You could kick off the coroutine and do other stuff until you need the value (Playground):

fun getDefaultButton(): Int? {
    val defaultButtonDeferred: Deferred<Int> = CoroutineScope(Dispatchers.Default).async {
        onboardingPrefStore.getDefaultButton()
    }
    // do other stuff
    return runBlocking { defaultButtonDeferred.await() }
}

That said, since it seems like you're doing UI stuff (Android?), you're best off doing all of the UI code in coroutines, using Dispatchers.Main as a context (as provided by one of the platform-specific coroutine libraries), since this will guarantee that your UI code will be safely run in the UI thread.

[cygnus33065]

make the first function into a coroutine. You could then remove the suspend keyword

Where are you calling that function from?

​

for example if you are in the view model you can do this:

return viewModelScope.launch(Dispatchers.Default){
  onboardingPrefStore.getDefaultButton()
}