Wait for LiveData result in a Kotlin coroutine

Question

I have a repository class with an asynchronous method returning User wrapped into a LiveData:

interface Repository {
    fun getUser(): LiveData<User>
}

In a ViewModel's coruotine scope I want to wait for a result of getUser() method and use an User instance.

this is what, I am looking for:

private fun process() = viewModelScope.launch {
   val user = repository.getUser().await()
   // do something with a user instance
}

I could not find LiveData<>.await() extension method, and any attempts to implement it. So before doing it my self, I wonder maybe there is some better way?

All solutions that I have found were about making getUser() a suspend method, but what if I can not change Repository?

Answer 1

You should be able to create an await() extension function using suspendCancellableCoroutine(). This probably is not exactly correct, but something along these lines should work:

public suspend fun <T> LiveData<T>.await(): T {
  return withContext(Dispatchers.Main.immediate) {
    suspendCancellableCoroutine { continuation ->
      val observer = object : Observer<T> {
        override fun onChanged(value: T) {
          removeObserver(this)
          continuation.resume(value)
        }
      }

      observeForever(observer)

      continuation.invokeOnCancellation {
        removeObserver(observer)
      }
    }
  }
}

This should return the first value emitted by the LiveData, without leaving an observer behind.