Modeling Retrofit responses with Sealed classes and Coroutines

Modeling Retrofit responses with Sealed classes and Coroutines at Android Worldwide.

Transcript

1. G E T S T R E A M . I O
   Modeling Retrofit
   Responses
   With Sealed Classes + Coroutines
   

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2. G E T S T R E A M . I O
   skydoves
   @github_skydoves
   Android Developer Advocate @ Stream
   Jaewoong Eum
   

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3. G E T S T R E A M . I O
   Architecture Network Request
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Presentation
   States
   View
   ViewModel
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   

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4. G E T S T R E A M . I O
   Architecture Network Request
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   Presentation
   States
   View
   ViewModel
   

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5. G E T S T R E A M . I O
   Architecture Network Request
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   Response
   Success
   - body
   - headers
   - status code
   Failure
   - error body
   - headers
   - status code
   Exception
   - IOException
   - UnKnownHostException
   - SSLHandshakeException
   - …
   Error
   

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6. G E T S T R E A M . I O
   Architecture Network Request Scenario
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Presentation
   States
   View
   ViewModel
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   

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7. G E T S T R E A M . I O
   Architecture
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Presentation
   States
   View
   ViewModel
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   Success Success
   Network Request Scenario
   

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8. G E T S T R E A M . I O
   Architecture
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Presentation
   States
   View
   ViewModel
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   Error
   Error
   Success Success
   Network Request Scenario
   

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9. G E T S T R E A M . I O
   Architecture
   Domain
   Interactors,
   Use case
   Interfaces
   Threading
   Presentation
   States
   View
   ViewModel
   Data
   Repository
   Remote
   DataSource
   Local
   DataSource
   Error
   Error
   Exception? Exception? Exception?
   Success Success
   Network Request Scenario
   

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10. G E T S T R E A M . I O
    interface PosterService {
    @GET("DisneyPosters.json")
    suspend fun fetchPosters(): List
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): List = try {
    posterService.fetchPosters()
    } catch (e: HttpException) {
    // error handling
    emptyList()
    } catch (e: Throwable) {
    // error handling
    emptyList()
    }
    }
    Retrofit API calls with Coroutines
    

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11. G E T S T R E A M . I O
    Retrofit API calls with Coroutines
    interface PosterService {
    @GET("DisneyPosters.json")
    suspend fun fetchPosters(): List
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): List = try {
    posterService.fetchPosters()
    } catch (e: HttpException) {
    // error handling
    emptyList()
    } catch (e: Throwable) {
    // error handling
    emptyList()
    }
    }
    Problem
    ● Results are ambiguous to callers
    ● Callers don't know the exception types
    val data = posterRemoteDataSource.invoke()
    if (data.isNotEmpty()) {
    ...
    }
    Success? or Failure?
    

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12. G E T S T R E A M . I O
    Architecture Sealed Classes
    Data
    Repository
    Remote
    DataSource
    Local
    DataSource
    Response
    Success
    - body
    - headers
    - status code
    Failure
    - error body
    - headers
    - status code
    Exception
    - IOException
    - UnKnownHostException
    - SSLHandshakeException
    - …
    Error
    Sealed Classes (=Result)
    

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13. G E T S T R E A M . I O
    Architecture
    Domain
    Interactors,
    Use case
    Interfaces
    Threading
    Presentation
    States
    View
    ViewModel
    Data
    Repository
    Remote
    DataSource
    Local
    DataSource
    Error
    Error
    try-catch
    Success Success
    Network Request Scenario
    

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14. G E T S T R E A M . I O
    Modeling responses Sealed Class
    sealed class NetworkResult {
    class Success(val data: T) : NetworkResult()
    class Error(val code: Int, val message: String?) : NetworkResult()
    class Exception(val e: Throwable) : NetworkResult()
    }
    ● NetowrkResult.Success: Success from the network request.
    ● NetowrkResult.Error: Failed from the network request.
    ● NetowrkResult.Exception: Unexpected exception. i.e. IOException, UnknownHostException
    

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15. G E T S T R E A M . I O
    Modeling responses Sealed Interfaces
    sealed interface ApiResult
    class ApiSuccess(val data: T) : ApiResult
    class ApiError(val code: Int, val message: String?) : ApiResult
    class ApiException(val e: Throwable) : ApiResult
    ● ApiSuccess: Success from the network request.
    ● ApiError: Failed from the network request.
    ● ApiException: Unexpected exception. i.e. IOException, UnknownHostException
    

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16. G E T S T R E A M . I O
    Modeling responses Sealed Interfaces
    sealed interface ApiResult
    sealed class ApiError(val code: Int, val message: String?) : ApiResult
    class BadRequest(val response: Response): ApiError(response.code(), response.message())
    class Unauthorized(val response: Response): ApiError(response.code(), response.message())
    class Forbidden(val response: Response): ApiError(response.code(), response.message())
    

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17. G E T S T R E A M . I O
    Modeling responses Sealed Interfaces
    when (val response = posterRemoteDataSource.invoke()) {
    is ApiError → {
    when (response) {
    is ApiError.BadRequest → Unit
    is ApiError.Unauthorized → Unit
    is ApiError.Forbidden → Unit
    }
    }
    sealed interface ApiResult
    sealed class ApiError(val code: Int, val message: String?) : ApiResult
    class BadRequest(val response: Response): ApiError(response.code(), response.message())
    class Unauthorized(val response: Response): ApiError(response.code(), response.message())
    class Forbidden(val response: Response): ApiError(response.code(), response.message())
    

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18. G E T S T R E A M . I O
    Modeling responses Sealed Classes vs Sealed Interfaces
    Sealed Classes Sealed Interfaces
    Declaration restrictions Same file Same module
    Inheritance limitations Single parent class Multiple sealed hierarchies
    API surfaces Selectively public Must be public
    

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19. G E T S T R E A M . I O
    Modeling responses Handling Retrofit responses
    Retrofit Response NetworkResult
    handleApi
    

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20. G E T S T R E A M . I O
    Modeling responses Handling Retrofit responses
    suspend fun handleApi(
    execute: suspend () -> Response
    ): NetworkResult {
    return try {
    val response = execute()
    val body = response.body()
    if (response.isSuccessful && body != null) {
    NetworkResult.Success(body)
    } else {
    NetworkResult.Error(code = response.code(), message = response.message())
    }
    } catch (e: HttpException) {
    NetworkResult.Error(code = e.code(), message = e.message())
    } catch (e: Throwable) {
    NetworkResult.Exception(e)
    }
    }
    

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21. G E T S T R E A M . I O
    Modeling responses
    suspend fun handleApi(
    execute: suspend () -> Response
    ): NetworkResult {
    return try {
    val response = execute()
    val body = response.body()
    if (response.isSuccessful && body != null) {
    NetworkResult.Success(body)
    } else {
    NetworkResult.Error(code = response.code(), message = response.message())
    }
    } catch (e: HttpException) {
    NetworkResult.Error(code = e.code(), message = e.message())
    } catch (e: Throwable) {
    NetworkResult.Exception(e)
    }
    }
    Handling Retrofit responses
    

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22. G E T S T R E A M . I O
    Modeling responses
    suspend fun handleApi(
    execute: suspend () -> Response
    ): NetworkResult {
    return try {
    val response = execute()
    val body = response.body()
    if (response.isSuccessful && body != null) {
    NetworkResult.Success(body)
    } else {
    NetworkResult.Error(code = response.code(), message = response.message())
    }
    } catch (e: HttpException) {
    NetworkResult.Error(code = e.code(), message = e.message())
    } catch (e: Throwable) {
    NetworkResult.Exception(e)
    }
    }
    Handling Retrofit responses
    

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23. G E T S T R E A M . I O
    Modeling responses
    suspend fun handleApi(
    execute: suspend () -> Response
    ): NetworkResult {
    return try {
    val response = execute()
    val body = response.body()
    if (response.isSuccessful && body != null) {
    NetworkResult.Success(body)
    } else {
    NetworkResult.Error(code = response.code(), message = response.message())
    }
    } catch (e: HttpException) {
    NetworkResult.Error(code = e.code(), message = e.message())
    } catch (e: Throwable) {
    NetworkResult.Exception(e)
    }
    }
    Handling Retrofit responses
    

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24. G E T S T R E A M . I O
    Modeling responses
    suspend fun handleApi(
    execute: suspend () -> Response
    ): NetworkResult {
    return try {
    val response = execute()
    val body = response.body()
    if (response.isSuccessful && body != null) {
    NetworkResult.Success(body)
    } else {
    NetworkResult.Error(code = response.code(), message = response.message())
    }
    } catch (e: HttpException) {
    NetworkResult.Error(code = e.code(), message = e.message())
    } catch (e: Throwable) {
    NetworkResult.Exception(e)
    }
    }
    Handling Retrofit responses
    

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25. G E T S T R E A M . I O
    interface PosterService {
    @GET("DisneyPosters.json")
    suspend fun fetchPosters(): Response>
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): NetworkResult> =
    handleApi { posterService.fetchPosters() }
    }
    Modeling responses Data Layer
    

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26. G E T S T R E A M . I O
    viewModelScope.launch {
    when (val response = posterRemoteDataSource.invoke()) {
    is NetworkResult.Success → posterFlow.emit(response.data)
    is NetworkResult.Error → errorFlow.emit("${response.code} ${response.message}")
    is NetworkResult.Exception → errorFlow.emit("${response.e.message}")
    }
    }
    Modeling responses ViewModel
    

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27. G E T S T R E A M . I O
    viewModelScope.launch {
    when (val response = posterRemoteDataSource.invoke()) {
    is NetworkResult.Success → posterFlow.emit(response.data)
    is NetworkResult.Error → errorFlow.emit(
    when (response.code) {
    400 → "BadRequest"
    401 → "Unauthorized"
    else → "Unknown"
    }
    )
    is NetworkResult.Exception → errorFlow.emit(response.e.message)
    }
    }
    Modeling responses ViewModel
    

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28. G E T S T R E A M . I O
    Architecture API data flow
    Presentation
    Repository
    Retrofit
    Domain
    

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29. G E T S T R E A M . I O
    Architecture API data flow
    Domain Presentation
    Repository
    Retrofit
    handleApi
    handleApi
    handleApi
    

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30. G E T S T R E A M . I O
    Architecture API data flow
    Domain Presentation
    Repository
    Retrofit
    handleApi
    handleApi
    handleApi
    

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31. G E T S T R E A M . I O
    Retrofit
    Retrofit
    CallAdapter
    Modeling responses Retrofit CallAdapter
    Response
    Exception
    Response Type
    

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32. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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33. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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34. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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35. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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36. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = NetworkResult.Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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37. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = NetworkResult.Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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38. G E T S T R E A M . I O
    class NetworkResultCall(
    private val proxy: Call
    ) : Call> {
    override fun enqueue(callback: Callback>) {
    proxy.enqueue(object : Callback {
    override fun onResponse(call: Call, response: Response) {
    val networkResult = handleApi { response }
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    override fun onFailure(call: Call, t: Throwable) {
    val networkResult = NetowrkResult.Exception(t)
    callback.onResponse(this@NetworkResultCall,
    Response.success(networkResult))
    }
    })
    }
    Modeling responses Custom Retrofit Call
    override fun execute(): Response> =
    throw NotImplementedError()
    override fun clone(): Call> =
    NetworkResultCall(proxy.clone())
    override fun request(): Request = proxy.request()
    override fun timeout(): Timeout = proxy.timeout()
    override fun isExecuted(): Boolean = proxy.isExecuted
    override fun isCanceled(): Boolean = proxy.isCanceled
    override fun cancel() {
    proxy.cancel()
    }
    

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39. G E T S T R E A M . I O
    class NetworkResultCallAdapter(
    private val resultType: Type
    ) : CallAdapter>> {
    override fun responseType(): Type = resultType
    override fun adapt(call: Call): Call> {
    return NetworkResultCall(call)
    }
    }
    Modeling responses Retrofit CallAdapter
    

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40. G E T S T R E A M . I O
    class NetworkResultCallAdapter(
    private val resultType: Type
    ) : CallAdapter>> {
    override fun responseType(): Type = resultType
    override fun adapt(call: Call): Call> {
    return NetworkResultCall(call)
    }
    }
    Modeling responses Retrofit CallAdapter
    

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41. G E T S T R E A M . I O
    class NetworkResultCallAdapterFactory private constructor() : CallAdapter.Factory() {
    override fun get(returnType: Type, annotations: Array, retrofit: Retrofit): CallAdapter<*, *>? {
    if (getRawType(returnType) != Call::class.java) {
    return null
    }
    val callType = getParameterUpperBound(0, returnType as ParameterizedType)
    if (getRawType(callType) != NetworkResult::class.java) {
    return null
    }
    val resultType = getParameterUpperBound(0, callType as ParameterizedType)
    return NetworkResultCallAdapter(resultType)
    }
    companion object {
    fun create(): NetworkResultCallAdapterFactory = NetworkResultCallAdapterFactory()
    }
    }
    Modeling responses Retrofit CallAdapter Factory
    

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42. G E T S T R E A M . I O
    class NetworkResultCallAdapterFactory private constructor() : CallAdapter.Factory() {
    override fun get(returnType: Type, annotations: Array, retrofit: Retrofit): CallAdapter<*, *>? {
    if (getRawType(returnType) != Call::class.java) {
    return null
    }
    val callType = getParameterUpperBound(0, returnType as ParameterizedType)
    if (getRawType(callType) != NetworkResult::class.java) {
    return null
    }
    val resultType = getParameterUpperBound(0, callType as ParameterizedType)
    return NetworkResultCallAdapter(resultType)
    }
    companion object {
    fun create(): NetworkResultCallAdapterFactory = NetworkResultCallAdapterFactory()
    }
    }
    Modeling responses Retrofit CallAdapter Factory
    

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43. G E T S T R E A M . I O
    class NetworkResultCallAdapterFactory private constructor() : CallAdapter.Factory() {
    override fun get(returnType: Type, annotations: Array, retrofit: Retrofit): CallAdapter<*, *>? {
    if (getRawType(returnType) != Call::class.java) {
    return null
    }
    val callType = getParameterUpperBound(0, returnType as ParameterizedType)
    if (getRawType(callType) != NetworkResult::class.java) {
    return null
    }
    val resultType = getParameterUpperBound(0, callType as ParameterizedType)
    return NetworkResultCallAdapter(resultType)
    }
    companion object {
    fun create(): NetworkResultCallAdapterFactory = NetworkResultCallAdapterFactory()
    }
    }
    Modeling responses Retrofit CallAdapter Factory
    

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44. G E T S T R E A M . I O
    val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(MoshiConverterFactory.create())
    .addCallAdapterFactory(NetworkResultCallAdapterFactory.create())
    .build()
    Modeling responses Retrofit CallAdapter
    

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45. G E T S T R E A M . I O
    val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(MoshiConverterFactory.create())
    .addCallAdapterFactory(NetworkResultCallAdapterFactory.create())
    .build()
    Modeling responses Retrofit CallAdapter
    interface PosterService {
    @GET("DisneyPosters.json")
    fun fetchPosters(): Call>>
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): NetworkResult> {
    return posterService.fetchPosters().await()
    }
    }
    

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46. G E T S T R E A M . I O
    val retrofit = Retrofit.Builder()
    .baseUrl(BASE_URL)
    .addConverterFactory(MoshiConverterFactory.create())
    .addCallAdapterFactory(NetworkResultCallAdapterFactory.create())
    .build()
    Modeling responses Retrofit CallAdapter
    interface PosterService {
    @GET("DisneyPosters.json")
    suspend fun fetchPosters(): NetworkResult>
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): NetworkResult> {
    return posterService.fetchPosters()
    }
    }
    

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47. G E T S T R E A M . I O
    Domain Presentation
    Repository
    Retrofit
    Retrofit
    CallAdapter
    Modeling responses Retrofit CallAdapter
    

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48. G E T S T R E A M . I O
    Modeling responses Extensions
    NetworkResult NetworkResult
    Map
    Combine
    Transformer
    

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49. G E T S T R E A M . I O
    Modeling responses Extensions
    suspend fun NetworkResult.onSuccess(
    executable: suspend (T) → Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Success) {
    executable(data)
    }
    }
    suspend fun NetworkResult.onError(
    executable: suspend (code: Int, message: String?) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Error) {
    executable(code, message)
    }
    }
    suspend fun NetworkResult.onException(
    executable: suspend (e: Throwable) → Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Exception) {
    executable(e)
    }
    }
    

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50. G E T S T R E A M . I O
    Modeling responses Extensions
    suspend fun NetworkResult.onSuccess(
    executable: suspend (T) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Success) {
    executable(data)
    }
    }
    suspend fun NetworkResult.onError(
    executable: suspend (code: Int, message: String?) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Error) {
    executable(code, message)
    }
    }
    suspend fun NetworkResult.onException(
    executable: suspend (e: Throwable) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Exception) {
    executable(e)
    }
    }
    

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51. G E T S T R E A M . I O
    Modeling responses Extensions
    suspend fun NetworkResult.onSuccess(
    executable: suspend (T) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Success) {
    executable(data)
    }
    }
    suspend fun NetworkResult.onError(
    executable: suspend (code: Int, message: String?) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Error) {
    executable(code, message)
    }
    }
    suspend fun NetworkResult.onException(
    executable: suspend (e: Throwable) -> Unit
    ): NetworkResult = apply {
    if (this is NetworkResult.Exception) {
    executable(e)
    }
    }
    

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52. G E T S T R E A M . I O
    Modeling responses Extensions
    viewModelScope.launch {
    val response = posterRemoteDataSource.invoke()
    response.onSuccess { posterList →
    posterFlow.emit(posterList)
    }.onError { code, message →
    errorFlow.emit("$code $message")
    }.onException {
    errorFlow.emit("${it.message}")
    }
    }
    

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53. G E T S T R E A M . I O
    Modeling responses Extensions
    viewModelScope.launch {
    val response = posterRemoteDataSource.invoke()
    response.onSuccess { posterList →
    posterFlow.emit(posterList)
    }.onError { code, message →
    errorFlow.emit("$code $message")
    }.onException {
    errorFlow.emit("${it.message}")
    }
    }
    suspend fun NetworkResult.map(
    transformer: (value: T) -> R
    ): NetworkResult {
    return if (this is NetworkResult.Success) {
    NetworkResult.Success(transformer(data))
    } else {
    this as NetworkResult
    }
    }
    

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54. G E T S T R E A M . I O
    Modeling responses Extensions
    viewModelScope.launch {
    val response = posterRemoteDataSource.invoke()
    response.map { posterList →
    posterList.first()
    }.onSuccess { poster →
    posterFlow.emit(poster)
    }.onError { code, message →
    errorFlow.emit("$code $message")
    }.onException {
    errorFlow.emit("${it.message}")
    }
    }
    suspend fun NetworkResult.map(
    transformer: (value: T) -> R
    ): NetworkResult {
    return if (this is NetworkResult.Success) {
    NetworkResult.Success(transformer(data))
    } else {
    this as NetworkResult
    }
    }
    

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55. G E T S T R E A M . I O
    Summarize
    ● Encapsulate raw data/exception from a network result
    ● Advanced error/exception handling
    ● We can expect the return type and improve them with functional operators
    ○ Monad
    ○ Functional Programming
    ○ Railway oriented programming
    ● Clear behaviors in domain/presentation layers by propagating the result
    

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56. G E T S T R E A M . I O
    Sandwich
    Other Solutions
    ● ApiResponse.Success: Success from the network request.
    ● ApiResponse.Error: Failed from the network request.
    ● ApiResponse.Exception: Unexpected exception. i.e. IOException, UnknownHostException.
    

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57. G E T S T R E A M . I O
    ● ApiResponse.getOrNull
    ● ApiResponse.getOrElse
    ● ApiResponse.getOrThrow
    Retrieve body data
    ● ApiSuccessModelMapper
    ● ApiErrorModelMapper
    ● map extensions
    Mapper
    ● ApiResponseOperator
    ● ApiResponseSuspendOperator
    ● Sandwich Global Operator
    Operator
    ● Merge extensions
    ● ApiResponseMergePolicy
    Merge
    ● ApiResponse.Success.statusCode
    ● ApiResponse.Failure.Error.statusCode
    StatusCode
    ● ApiResponse.toFlow()
    ● ApiResponse.toLiveData()
    Interoperability
    Sandwich
    Other Solutions
    

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58. G E T S T R E A M . I O
    Other Solutions Kotlin Result
    

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59. G E T S T R E A M . I O
    Other Solutions
    interface PosterService {
    @GET("DisneyPosters.json")
    suspend fun fetchPosters(): List
    }
    class PosterRemoteDataSource(
    private val posterService: PosterService
    ) {
    suspend operator fun invoke(): Result> {
    return kotlin.runCatching { posterService.fetchPosters() }
    }
    }
    Kotlin Result
    

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60. G E T S T R E A M . I O
    Other Solutions Arrow - Typed Functional Programming
    suspend operator fun invoke(): Either> {
    return Either.catch {
    posterService.fetchPosters()
    }.mapLeft { it }
    }
    

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61. G E T S T R E A M . I O
    Resources
    ● Retrofit
    ○ https://github.com/square/retrofit
    ○ https://square.github.io/retrofit/2.x/retrofit/retrofit2/CallAdapter.html
    ● Kotlin Sealed classes/interfaces
    ○ https://kotlinlang.org/docs/sealed-classes.html
    ● Functional Programming
    ○ https://en.wikipedia.org/wiki/Functional_programming
    ● Sandwich library
    ○ https://github.com/skydoves/sandwich
    ● Kotlin Result
    ○ https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-result/
    ○ https://github.com/Kotlin/KEEP/blob/master/proposals/stdlib/result.md
    ● Arrow
    ○ https://github.com/arrow-kt/arrow
    

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62. G E T S T R E A M . I O
    https://github.com/skydoves
    jaewoong.eum@getstream.io
    https://twitter.com/github_skydoves
    https://medium.com/@skydoves
    Contact
    

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63. G E T S T R E A M . I O
    Thank you.
    

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