worker

Constants.kt

object Constants {
    const val DATA_SUCCESS  = "DATA_SUCCESS"
    const val DATA_ERROR = "DATA_ERROR"
    const val WORKER_TAG = "WORKER_TAG"
}

implementations

   // GLIDE
    implementation 'com.github.bumptech.glide:glide:4.14.2'
    annotationProcessor 'com.github.bumptech.glide:compiler:4.14.2'

    // region Retrofit
    implementation "com.squareup.retrofit2:retrofit:2.9.0"
    implementation "com.squareup.retrofit2:converter-gson:2.9.0"
    implementation 'com.google.code.gson:gson:2.10.1'
    // endregion

    //Work Manager
    def work_version = "2.7.1"
    implementation "androidx.work:work-runtime-ktx:$work_version"

MainActivity.kt

private const val TAG = "MainActivity"
class MainActivity : AppCompatActivity() {
    lateinit var recyclerView: RecyclerView
    lateinit var myAdapter: ProductsAdapter
    lateinit var progressDialog: ProgressDialog
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        recyclerView = findViewById(R.id.recyclerView)
        progressDialog = waitingMessageDialog()

        progressDialog.show()

        val workerManager = WorkManager.getInstance(this)
        val request = OneTimeWorkRequestBuilder<MyWorker>()
            .addTag(Constants.WORKER_TAG)
            .build()

        workerManager.enqueue(request)
        workerManager.getWorkInfosByTagLiveData(Constants.WORKER_TAG).observe(this, Observer {workInfo->
            val info = workInfo?.find { it.id == request.id }
            when(info?.state){
                WorkInfo.State.SUCCEEDED ->{
                    progressDialog.cancel()
                    val myResponse = info.outputData.getString(Constants.DATA_SUCCESS)
                    val myData= Gson().fromJson(myResponse,ProductHolder::class.java)
                    sendToRecyclerView(myData)

                }
                WorkInfo.State.FAILED ->{
                    progressDialog.cancel()
                    val errorResponse = info.outputData.getString(Constants.DATA_ERROR)
                    Log.d(TAG, "Error: $errorResponse")}
                else ->{
                    progressDialog.cancel()
                }
            }
        })
//        RetrofiteAPI.getApi().getProducts().enqueue(object : Callback<Root>{
//            override fun onResponse(call: Call<Root>, response: Response<Root>) {
//                if (response.isSuccessful) {
//                    myAdapter = ProductsAdapter(this@MainActivity, response.body()?.products ?: ArrayList())
//                    recyclerView.setHasFixedSize(true)
//                    recyclerView.adapter = myAdapter
//                }
//            }
//
//            override fun onFailure(call: Call<Root>, t: Throwable) {
//                Log.d(TAG, "onFailure: ")
//            }
//        })

    }

    private fun sendToRecyclerView(productHolder: ProductHolder) {

        myAdapter = ProductsAdapter(this@MainActivity, productHolder.products ?: ArrayList())
        recyclerView.setHasFixedSize(true)
        recyclerView.adapter = myAdapter
    }

    fun waitingMessageDialog(): ProgressDialog {
        val progress: ProgressDialog = ProgressDialog(this)
        progress.setTitle("Loading")
        progress.setMessage("Please wait until downloading ..")
        return progress
    }
}

models.kt

data class Product(
    var id:Int = 0,
    var title: String? = null,
    var description: String? = null,
    var price:Int = 0,
    var discountPercentage:Double = 0.0,
    var rating:Double = 0.0,
    var stock:Int = 0,
    var brand: String? = null,
    var category: String? = null,
    var thumbnail: String? = null
)


data class ProductHolder(
    var products: ArrayList<Product>? = null,
    var total:Int = 0,
    var skip:Int = 0,
    var limit:Int = 0
)

MyWorker.kt

class MyWorker(context: Context,paras: WorkerParameters):Worker(context,paras) {

    override fun doWork(): Result {
        val api = RetrofiteAPI.getApi().getProducts()
        val productData = api.execute()
        try{
            if (productData.isSuccessful) {
                /// Pair("productData",productData.body().products)
                // "productData" to productData.body().products
                val data = Gson().toJson(productData.body()).toString()
                return Result.success(workDataOf(Constants.DATA_SUCCESS to data))
            } else {
                return Result.failure(workDataOf(Constants.DATA_ERROR to productData.errorBody().toString()))
            }
        }catch (e:java.lang.Exception){
            return Result.failure(workDataOf(Constants.DATA_ERROR to e.message))

        }
    }
}

RetrofitAPI.kt

interface NetworkAPI{
    @GET("products")
    fun getProducts(): Call<ProductHolder>
}

class RetrofiteAPI {
    companion object{
        fun getApi():NetworkAPI{
            val retrofit = Retrofit.Builder()
                .baseUrl("https://dummyjson.com/")
                .addConverterFactory(GsonConverterFactory.create())
                .build()
            return retrofit.create(NetworkAPI::class.java)
        }
    }

}