Sealed class | MVVM | Retrofit | RecyclerView | Recycler Adapter | Coroutines Flow | Image Loader in Adapter

 1. RetrofitService

object RetrofitService {
    private const val URL = "https://jsonplaceholder.typicode.com/"
    private val loggingInterceptor = HttpLoggingInterceptor().apply {
        level = HttpLoggingInterceptor.Level.BODY
    }

    private val client = OkHttpClient.Builder()
        .addInterceptor(loggingInterceptor)
        .build()

    fun getRetroService(): ApiService {
        return Retrofit.Builder()
            .addConverterFactory(GsonConverterFactory.create())
            .baseUrl(URL)
            .build().create(ApiService::class.java)
    }
}

2. ApiService

interface ApiService {
    @GET("photos")
    suspend fun getPhoto():List<PhotoResponseItem>
}
3. ApiStateController
sealed class ApiStateController {
    object Loading : ApiStateController()
    object Empty : ApiStateController()
    data class Success(val data: List<PhotoResponseItem>) : ApiStateController()
    data class Failure(val msg: String) : ApiStateController()
}
4. PhotoRepository
class PhotoRepository(private val apiService: ApiService) {

    fun getPhoto():Flow<List<PhotoResponseItem>> = flow {
        emit(apiService.getPhoto())
    }.flowOn(Dispatchers.IO)
}
5.PhotoViewModel
class PhotoViewModel(private val photoRepository: PhotoRepository) : ViewModel() {
    private val _photo: MutableStateFlow<ApiStateController> =
        MutableStateFlow(ApiStateController.Empty)
    val photo: StateFlow<ApiStateController>
        get() = _photo

    fun getPhoto() {
        viewModelScope.launch {
            _photo.value = ApiStateController.Loading
            photoRepository.getPhoto()
                .catch { e ->
                    _photo.value = ApiStateController.Failure(e.message.toString())
                }.collect { data ->
                    _photo.value = ApiStateController.Success(data)
                }
        }
    }
}
6.PhotoViewModelFactory
class PhotoViewModelFactory(private val photoRepository: PhotoRepository) :
    ViewModelProvider.NewInstanceFactory() {

    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return PhotoViewModel(photoRepository) as T
    }
}
7.PhotoActivity
class PhotoActivity : AppCompatActivity() {
    private lateinit var photoViewModel: PhotoViewModel
    private lateinit var binding: ActivityPhotoBinding
    private lateinit var photoAdapter: PhotoAdapter
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_photo)
        initRecyclerView()

        val api = RetrofitService.getRetroService()
        val repository = PhotoRepository(api)
        val factory = PhotoViewModelFactory(repository)
        photoViewModel = ViewModelProvider(this, factory)[PhotoViewModel::class.java]
        photoViewModel.getPhoto()
        getPhoto()
    }

    private fun getPhoto() {
        lifecycle.coroutineScope.launchWhenStarted {
            photoViewModel.photo.collect { it ->
                when (it) {
                    ApiStateController.Empty -> {
                        Log.d("Response====", "===Empty=====")

                    }

                    is ApiStateController.Failure -> {
                        Log.d("Response====", "===Error:= ${it.msg}=====")

                        binding.progress.visibility = View.GONE
                        Snackbar.make(binding.root, it.msg, Snackbar.LENGTH_SHORT).show()

                    }

                    ApiStateController.Loading -> {
                        binding.progress.visibility = View.VISIBLE
                        Log.d("Response====", "===Loading=====")
                    }

                    is ApiStateController.Success -> {
                        binding.progress.visibility = View.GONE
                        Log.d("Response is===", "${it.data}")
                        photoAdapter.setData(it.data)
                        photoAdapter.notifyDataSetChanged()

                    }
                }
            }
        }
    }

    private fun initRecyclerView() {
        photoAdapter = PhotoAdapter(ArrayList())
        binding.recyclerView.apply {
            setHasFixedSize(true)
            adapter = photoAdapter
            layoutManager = LinearLayoutManager(this@PhotoActivity)
        }
    }

}
8. PhotoAdapter
class PhotoAdapter(private var photoList: List<PhotoResponseItem>) :
    RecyclerView.Adapter<PhotoAdapter.PhotoViewHolder>() {
    lateinit var binding: EachRowBinding
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PhotoViewHolder {
        binding = EachRowBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        return PhotoViewHolder(binding.root)
    }

    override fun onBindViewHolder(holder: PhotoViewHolder, position: Int) {
        binding.id.text = photoList[position].id.toString()
        binding.title.text = photoList[position].title
        Glide
            .with(binding.thumbnailUrl)
            .load(photoList[position].thumbnailUrl)
            .centerCrop()
            .into(binding.thumbnailUrl);

    }

    override fun getItemCount(): Int {
        return photoList.size
    }

    class PhotoViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    }

    fun setData(photoData: List<PhotoResponseItem>) {
        this.photoList = photoData
        notifyDataSetChanged()
    }


}
9. photo_activity
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <data>

    </data>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

        <ProgressBar
            android:id="@+id/progress"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:layout_marginTop="30dp"
            android:visibility="gone" />

    </RelativeLayout>
</layout>

10. each_row.xml
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <data>

    </data>

    <androidx.cardview.widget.CardView xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:elevation="8dp"
        android:orientation="vertical"
        app:cardCornerRadius="8dp"
        app:cardUseCompatPadding="true">

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <ImageView
                android:id="@+id/thumbnailUrl"
                android:layout_width="100dp"
                android:layout_height="100dp" />

            <LinearLayout
                android:id="@+id/layout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginLeft="10dp"
                android:layout_toRightOf="@+id/thumbnailUrl"
                android:orientation="vertical">

                <TextView
                    android:id="@+id/title"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:maxLines="1"
                    android:textAppearance="@style/TextAppearance.AppCompat.Medium"
                    tools:text="Hello world" />

                <TextView
                    android:id="@+id/id"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_marginTop="5dp"
                    tools:text="1" />

            </LinearLayout>

        </RelativeLayout>


    </androidx.cardview.widget.CardView>
</layout>