Offline Caching in Android Studio

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Overview

Hello World


Code

 plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-kapt'
    id 'dagger.hilt.android.plugin'
 }
 // Dagger Hilt
 def hilt_version = "2.38.1"
 implementation "com.google.dagger:hilt-android:$hilt_version"
 kapt "com.google.dagger:hilt-compiler:$hilt_version"

 // Retrofit
 def retrofit_version = "2.9.0"
 implementation "com.squareup.retrofit2:retrofit:$retrofit_version"
 implementation "com.squareup.retrofit2:converter-gson:$retrofit_version"
 implementation "com.squareup.okhttp3:logging-interceptor:4.9.1"

 // Coroutines
 def coroutines_version = "1.6.0"
 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$coroutines_version"
 implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines_version"

 // ViewModel and LiveData
 def lifecycle_version = "2.4.0"
 implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
 implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"

 // AndroidX for Activity used for Dependency Injection
 def activity_version = "1.4.0"
 implementation "androidx.activity:activity-ktx:$activity_version"

 // AndroidX for Fragment used for Dependency Injection
 def fragment_version = "1.4.1"
 implementation "androidx.fragment:fragment-ktx:$fragment_version"
 debugImplementation "androidx.fragment:fragment-testing:$fragment_version"

 // Room Database
 def room_version = "2.4.0"
 implementation "androidx.room:room-runtime:$room_version"
 kapt "androidx.room:room-compiler:$room_version"
 implementation "androidx.room:room-ktx:$room_version"
 annotationProcessor "androidx.room:room-compiler:$room_version"

 // Glide
 def glide_version = "4.11.0"
 implementation "com.github.bumptech.glide:glide:$glide_version"
 annotationProcessor "com.github.bumptech.glide:compiler:$glide_version"
 /*
 * Raj Kanchan
 * * Data Resource: https://random-data-api.com/documentation
 *
 * */

 @Entity(tableName = "restaurants")
 data class Restaurant(
    @PrimaryKey(autoGenerate = false) val uid: String,
    val name: String,
    val description: String,
    val logo: String,
    val address: String
 )
 interface RestaurantApi {
    companion object {
        const val BASE_URL = "https://random-data-api.com/api/"
    }

    @GET("restaurant/random_restaurant?size=20")
    suspend fun getRestaurants(): List<Restaurant>
 }
 @Dao
 interface RestaurantDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insertRestaurant(restaurants: List<Restaurant>)

    @Query("DELETE FROM restaurants")
    suspend fun deleteAllRestaurants()

    @Query("SELECT * FROM restaurants")
    fun getRestaurants(): Flow<List<Restaurant>>
 }
 @Database(entities = [Restaurant::class], version = 1)
 abstract class RestaurantDatabase : RoomDatabase() {
    abstract fun getRestaurantDao(): RestaurantDao
 }
 class RestaurantRepository @Inject constructor(
    private val restaurantApi: RestaurantApi,
    private val restaurantDatabase: RestaurantDatabase
 ) {
    private val restaurantDao = restaurantDatabase.getRestaurantDao()
    fun getRestaurants() =
        networkBoundResource(query = { restaurantDao.getRestaurants() }, fetch = {
            delay(2000)
            restaurantApi.getRestaurants()
        }, saveFetchResult = { restaurants ->
            restaurantDatabase.withTransaction {
                restaurantDao.deleteAllRestaurants()
                restaurantDao.insertRestaurant(restaurants)
            }
        })
 }
 @Module
 @InstallIn(SingletonComponent::class)
 object AppModule {
    @Provides
    @Singleton
    fun provideRetrofit(): Retrofit = Retrofit.Builder().baseUrl(RestaurantApi.BASE_URL)
        .addConverterFactory(GsonConverterFactory.create()).build()

    @Provides
    @Singleton
    fun provideRestaurants(retrofit: Retrofit): RestaurantApi =
        retrofit.create(RestaurantApi::class.java)

    @Provides
    @Singleton
    fun provideDatabase(app: Application): RestaurantDatabase =
        Room.databaseBuilder(app, RestaurantDatabase::class.java, "restaurantDB").build()
 }
 sealed class Resource<T>(
    val data: T? = null,
    val error: Throwable? = null
 ) {
    class Success<T>(data: T) : Resource<T>()
    class Loading<T>(data: T? = null) : Resource<T>()
    class Error<T>(throwable: Throwable, data: T? = null) : Resource<T>(data, throwable)
 }
 inline fun <ResultType, RequestType> networkBoundResource(
    crossinline query: () -> Flow<ResultType>,
    crossinline fetch: suspend () -> RequestType,
    crossinline saveFetchResult: suspend (RequestType) -> Unit,
    crossinline shouldFetch: (ResultType) -> Boolean = { true }
 ) = flow {
    val data = query().first()
    val flow = if (shouldFetch(data)) {
        emit(Resource.Loading(data))
        try {
            saveFetchResult(fetch())
            query().map { Resource.Success(it) }
        } catch (throwable: Throwable) {
            query().map { Resource.Error(throwable, it) }
        }
    } else {
        query().map { Resource.Success(it) }
    }
    emitAll(flow)
 }
 @HiltViewModel
 class RestaurantViewModel @Inject constructor(restaurantRepository: RestaurantRepository) :
    ViewModel() {
    private val restaurantMutableLiveData = MutableLiveData<List<Restaurant>>()
    val restaurants = restaurantRepository.getRestaurants().asLiveData()
 }
 class RestaurantAdapter :
    ListAdapter<Restaurant, RestaurantAdapter.RestaurantViewHolder>(RestaurantComparator()) {
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RestaurantViewHolder {
        val binding =
            RestaurantItemBinding.inflate(LayoutInflater.from(parent.context), parent, false)
        return RestaurantViewHolder(binding)
    }

    override fun onBindViewHolder(holder: RestaurantViewHolder, position: Int) {
        val currentItem = getItem(position)
        if (currentItem != null) {
            holder.bind(currentItem)
        }
    }

    class RestaurantViewHolder(private val binding: RestaurantItemBinding) :
        RecyclerView.ViewHolder(binding.root) {
        fun bind(restaurant: Restaurant) {
            binding.apply {
                Glide.with(itemView).load(restaurant.logo).into(imgRestaurantLogo)
                tvRestaurantTitle.text = restaurant.name
                tvRestaurantDescription.text = restaurant.description
                tvRestaurantAddress.text = restaurant.address
            }
        }
    }

    class RestaurantComparator : DiffUtil.ItemCallback<Restaurant>() {
        override fun areItemsTheSame(oldItem: Restaurant, newItem: Restaurant) =
            oldItem.uid == newItem.uid

        override fun areContentsTheSame(oldItem: Restaurant, newItem: Restaurant) =
            oldItem == newItem
    }
 }
 @AndroidEntryPoint
 class RestaurantActivity : AppCompatActivity() {
    private val restaurantViewModel: RestaurantViewModel by viewModels()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding = ActivityRestaurantBinding.inflate(layoutInflater)
        setContentView(binding.root)
        val restaurantAdapter = RestaurantAdapter()
        binding.apply {
            recyclerViewRestaurant.apply {
                adapter = restaurantAdapter
                layoutManager = LinearLayoutManager(this@RestaurantActivity)
            }

            restaurantViewModel.restaurants.observe(this@RestaurantActivity) { result ->
                restaurantAdapter.submitList(result.data)
                progressBar.isVisible = result is Resource.Loading && result.data.isNullOrEmpty()
                tvError.isVisible = result is Resource.Error && result.data.isNullOrEmpty()
                tvError.text = result.error?.localizedMessage
            }
        }
    }
 }
 @HiltAndroidApp
 class MainApplication : Application() {
 }
 <?xml version="1.0" encoding="utf-8"?>
 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="120dp"
    android:padding="20dp">

    <ImageView
        android:id="@+id/imgRestaurantLogo"
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:src="@drawable/ic_launcher_background"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tvRestaurantTitle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/imgRestaurantLogo"
        app:layout_constraintTop_toTopOf="@id/imgRestaurantLogo" />

    <TextView
        android:id="@+id/tvRestaurantDescription"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        app:layout_constraintEnd_toEndOf="@+id/tvRestaurantTitle"
        app:layout_constraintStart_toStartOf="@+id/tvRestaurantTitle"
        app:layout_constraintTop_toBottomOf="@+id/tvRestaurantTitle" />

    <TextView
        android:id="@+id/tvRestaurantAddress"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        app:layout_constraintEnd_toEndOf="@+id/tvRestaurantTitle"
        app:layout_constraintStart_toStartOf="@+id/tvRestaurantTitle"
        app:layout_constraintTop_toBottomOf="@+id/tvRestaurantDescription" />

 </androidx.constraintlayout.widget.ConstraintLayout>
 <?xml version="1.0" encoding="utf-8"?>
 <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".features.restaurants.RestaurantActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerViewRestaurant"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="false"
        android:padding="5dp"
        tools:listitem="@layout/restaurant_item" />

    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="gone"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:visibility="visible" />

    <TextView
        android:id="@+id/tvError"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="Error Message"
        android:visibility="gone"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:visibility="visible" />

 </androidx.constraintlayout.widget.ConstraintLayout>

Reference



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