How to handle API error response using retrofit with android kotlin

Question

My Android kotlin code:

viewModelScope.launch(Dispatchers.IO) {
            _userAuth.postValue((Resource.Loading()))
            try {
                val res = repository.userSignUp(SignupRequest("test", "[email protected]", "password"))
                if (res.isSuccessful) {
                    res.body()?.let {
                        _userAuth.postValue(Resource.Success(it))
                    }
                } else {
                    // Handle error here...
                }
            } catch (e: IOException) {
                Timber.d(e.message)
            } catch (e: HttpException) {
                Timber.d(e.message)
            }
        }
}

I developed nodejs api where user can Signup and Signin. How to handle errors if reponse is not successful. My json response error model look like this:

{
  "error": {
      "message": "Username is already taken",
      "code": 422
   }
}

error.message property's value could be anything according to error e.g. Email is already taken, Email is invalid, etc. How to parse with own custom kotlin data class?

Answer 1

Your sealed generic Resource class should also handle the error. Something like this

sealed class Resource<T> {
  data class Success<T>(val data: T) : Resource<T>()
  data class Error<T>(val error: Throwable) : Resource<T>()
  class Loading<T> : Resource<T>()
}

Then, inside VM

if (res.isSuccessful) {
   res.body()?.let {
     _userAuth.postValue(Resource.Success(it))
   }
} else {
   // Handle error here...
   _userAuth.postValue(Resource.Error(it))
}

In UI, when observing it, simply returning api's own failure message

viewModel._userAuth.observe(viewLifecycleOwner){
when (it) {
            is Resource.Success -> onSuccess(it.data)
            is Resource.Error -> Toast.makeText(requireContext(), it.error.message, Toast.LENGTH_LONG).show()
            is Resource.Loading -> onLoading()
        }
}