Tukukkk

I have been experimenting Android Architecture Pattern from over 2 weeks. I have been strugling to understand what code goes where, ViewModel or Repository or somewhere else?

It really looked nice when I was learning and going through sample apps. So, I decided to use it in real life. I got stuck when I wanted to perform the login on the login button click. I couldn't understand the flow how it really should go.

The first thing was to rescue was this github issue thread, https://github.com/googlesamples/android-architecture-components/issues/63#issuecomment-310422475

Firing an event when user click on a button. All the samples and blog posts were really good pointing at loading data when the fragment starts and observing thing. But, this thing didn't worked for me. So I came out with my own solution that observes util it reaches it's end state. Like a network resource starts loading, and completes with success or error. That means there will be 2 callbacks to the observer, when the data loading starts and when it completes.

That looked something like this:

interface StatefulResource<T> {



    /**

     * This method return if the resource is in it's end state. All the events had occurred

     * and there are no other events left to follow for them.

     *

     * @return true/false based if the current state is end state or not

     */

    fun isEndState(): Boolean



}



class Resource<T> private constructor() : StatefulResource<T> {



    var state: Int? = null

        private set

    var result: Result? = null



    companion object {

        const val STATE_LOADING = 1

        const val STATE_SUCCESS = 2

        const val STATE_ERROR = 3



        fun <T> result(result: Result) = Resource<T>().apply { this.result = result }

        fun <T> loading() = Resource<T>().apply { this.state = STATE_LOADING }

    }



    override fun isEndState() = (state == STATE_ERROR) or (state == STATE_SUCCESS)



    fun isSuccessful() = state == STATE_SUCCESS

}



fun <J : StatefulResource<T>, T> LiveData<J>.observeStatefully(

    lifecycleOwner: LifecycleOwner,

    observer: Observer<J>

) {

    val liveData = this

    val internalObserver = object : Observer<J> {

        override fun onChanged(resource: J) {

            observer.onChanged(resource)

            if (resource.isEndState().orFalse()) {

                liveData.removeObserver(this)

            }

        }

    }

    observe(lifecycleOwner, internalObserver)

}

Now, what really happened here is how to return data from the API call. How to abstract things from the repository side and simplify the things using coroutines. I came up to this article and I made something after reading it.

I came up with something like this:

sealed class Result

data class Success<out T : Any>(val data: T?) : Result()

data class Failure(val message: String, val error: Throwable?) : Result()



interface CommonResponse<T : Any> {

    var status: Int

    var message: String

    var data: T?



    fun isValid() = status == 1



    fun mapResult(): Result = if (isValid())

        Success(data)

    else

        Failure(message, null)

}



/**

 * This extension method enqueues the call using the coroutine and

 * return the Result instance with Success or Failure

 */

suspend fun <T, S : CommonResponse<T>> Call<S>.getResult(): Result = try {

    this.enqueueAwait().mapResult()

} catch (error: Throwable) {

    Failure("Something went wrong", error)

}

Now, in the activity I have to write this code:

  viewModel.login(mBinding.editEmail.value.trim(), mBinding.editPassword.value, null)

                    .observeStatefully(viewLifecycleOwner, Observer { resource ->

                        mBinding.resource = resource



                        when (resource.state) {

                            Resource.STATE_SUCCESS -> {

                                navController.navigate(R.id.nav_action_fragment_sign_in_to_fragment_home)

                            }

                        }

                    })

I think, I have duplicated some things with this pattern. Like sealed class Result and Resource both can tell me the state of the result (Success or Failure and STATE_SUCCESS or STATE_FAILURE). So, instead of making things more clear, I made them unclear. Is there any better way? (This is certainly not the better one)

One more thing, I am finding difficult to understand is, when Login response, comes where should I write the logic of storing user information? Like in the repository I should write my logic of storing it into the prefs? Or inside the view model? What's the better way?

I couldn't find a sample that actually performs only networking with retrofit. How should I handle and architect this kind of apps?