(Code Saved For Later) Callback interface for android api requests without livedata. Not plugnplay but that shouldn't be a problem. It could probably be done with one less class...

APIRequest.kt

package any

import android.util.Log
import any.model.AppException
import any.model.NetworkState
import any.LiveModelCallback2
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response

class APIRequest<T>(
        val request: Call<T>,
        var onSuccess:((result: T) -> Unit)? = null,
        var onError:((acc: NetworkState) -> Unit)? = null
) {
    var canceled = false

    init {
        request.enqueue(object: SimplifiedCallback<T>() {
            override fun onSuccess(body: T) {
                super.onSuccess(body)
                if (canceled) {
                    return
                }
                onSuccess?.invoke(body)
            }

            override fun handleException(exception: AppException, code: Int?, errorData: String?) {
                super.handleException(exception, code, errorData)
                if (canceled) {
                    return
                }
                val error = NetworkState.error(exception.message, code ?: LiveModelCallback2.CODE_UNKNOWN, errorData)
                onError?.invoke(error)
            }
        })
    }
}

open class SimplifiedCallback<T> : Callback<T> {
    init {
    }

    override fun onResponse(call: Call<T>?, response: Response<T>?) {
        val body = response?.body()
        if (response?.isSuccessful == true && body != null ) {
            onSuccess(body)
        } else {
            val exception = AppException("Request failed: ${response?.code()} ${response?.message()}")
            handleException(exception, response?.code(), response?.errorBody()?.string())
        }
    }

    open fun onSuccess(body: T) {

    }

    override fun onFailure(call: Call<T>?, t: Throwable?) {
        val exception = AppException(t)
        handleException(exception)
    }

    open fun handleException(exception: AppException, code: Int? = null, errorData: String? = null) {
        Log.e(BuildConfig.TAG, exception.message, exception)
    }
}