Kotlin coroutines - gracefully handling errors from suspend functions

Question

Trying to implement graceful handling of the errors with suspend functions that are called from async methods, How to catch the error thrown by a suspend method.

Answer 1

I would use a CoroutineExceptionHandler to make your coroutines fail gracefully:

1) Define the handler:

val exceptionHandler = CoroutineExceptionHandler { context, error ->
    // Do what you want with the error
    Log.d(TAG, error)
}

2) Refactor your findById function to be executed within an IO context and make your ui code main safe:

suspend fun findById(id : Int) : User? = withContext(Dispatchers.IO){
    when(id){
        0 -> throw Exception("not valid")
        else -> return@withContext User(id)
    }
}

3. Launch your job within MainScope (and so update the ui), passing exceptionHandler to launch coroutine builder in order to catch the exception:

val exceptionHandler = CoroutineExceptionHandler { _, error ->
     // Do what you want with the error
    Log.d(TAG, error)
}

MainScope().launch(exceptionHandler) {
     val user = delegate?.findById(userId)
        user?.let {
            Timber.v(it.toString())
        }
}