Leveraging Sealed Classes in Kotlin

Sealed classes are much more than fancy enums. They are powerful composite types which can be useful in many ways. Common problems like exception handling and state representation become easier to manage with sealed classes. We will contrast traditional solutions, with modern ones using Kotlin.

Transcript

1. Leveraging 
 Sealed Classes Sanchita Agarwal / @sanchita_ag
2. simple.org • Sealed classes in our project • All examples are derived from this project
3. What to expect?
4. Deal with failures Build better app experience for your users
5. Modelling of view state Make your code easy to maintain
6. Whoops…
7. What is a failure?
9. button.setOnClickListener { login("me@obviously", "password123") }
10. button.setOnClickListener { login("me@obviously", "password123") }
11. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen }
12. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen }
13. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen }
14. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen }
15. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen }
16. fun login(username: String, password: String) { val response = loginCall .execute(username, password) //TODO Parse login response //TODO Save user state //TODO Go to home screen }
17. fun login(username: String, password: String) { val response = loginCall .execute(username, password) if (response.isSuccessful) { } //TODO Save user state //TODO Go to home screen }
18. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) } //TODO Go to home screen }
19. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } }
20. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } }
27. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } }
28. “The very worst error messages are those that don't exist.”
29. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog("Our servers are down") } }
30. App is crashing!
31. fun login(username: String, password: String) { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog("Our servers are down") } }
32. Why did we not think of this before? !
33. try { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog("Our servers are down!") } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
35. Airplane mode ✈
36. try { val response = loginCall .execute(username, password) val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog("Our servers are down!") } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
37. Catch-all error!
38. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
39. API contract!
41. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
42. if (response.isSuccessful) { saveToken(data.authToken) showHomeScreen() }
43. if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } }
44. if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog(data.errorMessage) } }
45. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog(data.errorMessage) } } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
46. Sun is shining again… ☀
47. Until its not! ⛈
48. java.lang.NullPointerException
49. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog(data.errorMessage) } } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
51. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog(data.errorMessage) } } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
52. Possible Problems • Poor failure handling • Hard to read • Multiple responsibilities
53. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen } Multiple responsibilities
54. fun login(username: String, password: String) { //TODO Make login request //TODO Parse login response //TODO Save user data //TODO Go to home screen } Separating concerns
55. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { showErrorDialog(data.errorMessage) } } else { when (response.code()) { 408 -> showErrorDialog("Connection issue") 500 -> showErrorDialog("Our servers are down!") else -> showErrorDialog("Something went wrong") } } } catch (error: IOException) { Log.e("Exception!", error.stackTrace.toString()) }
56. class LoginFailure(val error: String)
57. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { LoginFailure(data.errorMessage) } } else { when (response.code()) { 400 -> LoginFailure("Connection issue") 500 -> LoginFailure("Our servers are down!") else -> LoginFailure("Something went wrong") } } } catch (error: IOException) { LoginFailure("Exception occurred") }
58. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { saveToken(data.authToken) showHomeScreen() } else { LoginFailure(data.errorMessage) } } else { when (response.code()) { 408 -> LoginFailure("Connection issue") 500 -> LoginFailure("Our servers are down!") else -> LoginFailure("Something went wrong") } } } catch (error: IOException) { LoginFailure("Exception occurred") }
59. class LoginSuccess(val token: String) class LoginFailure(val error: String)
60. try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { LoginSuccess(data.authToken) } else { LoginFailure(data.errorMessage) } } else { when (response.code()) { 408 -> LoginFailure("Connection issue") 500 -> LoginFailure("Our servers are down!") else -> LoginFailure("Something went wrong") } } } catch (error: IOException) { LoginFailure("Exception occurred") }
61. class LoginSuccess(val token: String) class LoginFailure(val error: String)
62. class LoginSuccess(val token: String): LoginResult() class LoginFailure(val error: String): LoginResult()
63. fun login(username: String, password: String): LoginResult
64. class Success(val token: String): LoginResult() class Failure(val error: String): LoginResult()
65. return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { Success(data.authToken) } else { Failure(data.errorMessage) } } else { when (response.code()) { 408 -> Failure("Connection issue") 500 -> Failure("Our servers are down!") else -> Failure("Something went wrong") } } } catch (error: IOException) { Failure("Exception occurred") }
66. return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { Success(data.authToken) } else { Failure(data.errorMessage) } } else { when (response.code()) { 408 -> Failure("Connection issue") 500 -> Failure("Our servers are down!") else -> Failure("Something went wrong") } } } catch (error: IOException) { Failure(“Exception occurred”) }
67. return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) { Success(data.authToken) } else { Failure(data.errorMessage) } } else { when (response.code()) { 408 -> Failure("Connection issue") 500 -> Failure("Our servers are down!") else -> Failure("Something went wrong") } } } catch (error: IOException) { Failure("Exception occurred") }
68. Possible Problems • Poor failure handling • Hard to read • Multiple responsibilities
69. Failures Failure(data.errorMessage) Failure("Connection issue") Failure("Our servers are down!") Failure("Something went wrong") Failure("Exception occurred")
70. –a wise woman “Failures need to be treated as first class citizens”
71. Failure(data.errorMessage) -> INVALID_USER Failure("Connection issue") -> CONNECTION_ERROR
 Failure("Our servers are down!") -> SERVER_ERROR Failure("Something went wrong") -> UNEXPECTED_ERROR Failure("Exception occurred") -> EXCEPTION_OCCURRED
72. enum class Failures{ INVALID_USER, CONNECTION_ERROR, SERVER_ERROR, UNEXPECTED_ERROR, EXCEPTION_OCCURRED }
73. fun login(username: String, password: String): LoginResult { return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) Success(data.authToken) else INVALID_USER } else { when (response.code()) { 408 -> CONNECTION_ERROR 500 -> SERVER_ERROR else -> UNEXPECTED_ERROR } } } catch (error: IOException) { EXCEPTION_OCCURRED } }
74. enum class LoginResult{ SUCCESS, INVALID_USER, CONNECTION_ERROR, SERVER_ERROR, UNEXPECTED_ERROR, EXCEPTION_OCCURRED }
75. fun login(username: String, password: String): LoginResult { return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) SUCCESS(data.authToken) else INVALID_USER } else { when (response.code()) { 408 -> CONNECTION_ERROR 500 -> SERVER_ERROR else -> UNEXPECTED_ERROR } } } catch (error: IOException) { EXCEPTION_OCCURRED } }
76. • Cannot carry state • Restricted to being just values Disadvantages of Enums
77. Drumroll please…
78. Sealed classes
79. Sealed classes • Represent restricted class hierarchies • A value can have one of the types from a limited set, but cannot have any other type.
80. sealed class Vehicle { class TwoWheeler : Vehicle() class FourWheeler : Vehicle() }
81. enum class LoginResult{ SUCCESS, INVALID_USER, CONNECTION_ERROR, SERVER_ERROR, UNEXPECTED_ERROR, EXCEPTION_OCCURRED }
82. sealed class LoginResult { class Success : LoginResult() class InvalidUser : LoginResult() class ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
83. sealed class LoginResult { class Success(val data: String) : LoginResult() class InvalidUser : LoginResult() class ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
84. sealed class LoginResult { data class Success(val data: String) : LoginResult() class InvalidUser : LoginResult() class ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
85. sealed class LoginResult { data class Success(val data: String) : LoginResult() class InvalidUser : LoginResult() class ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
86. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
87. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() class ServerError : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
88. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
89. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() class UnexpectedError : LoginResult() class NetworkException : LoginResult() }
90. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException : LoginResult() }
91. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException : LoginResult() }
92. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException(val cause: Exception) : LoginResult() }
93. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException(val cause: Exception) : LoginResult() }
94. Possible Problems • Poor failure handling • Hard to read • Multiple responsibilities
95. fun login(username: String, password: String): LoginResult { return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) Success(data.authToken) else InvalidUser } else { when (response.code()) { 408 -> ConnectionError 500 -> ServerError(response.errorMessage) else -> UnexpectedError(response.code()) } } } catch (e: Exception) { NetworkException(e) } }
96. Possible Problems • Poor failure handling • Hard to read • Multiple responsibilities
97. Advantages of Sealed class
98. 1. All possible results in one place
99. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException(val cause: Exception) : LoginResult() }
100. 2. Helps you think of all outcomes
101. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() data class UserLocked(val duration: Long): LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException(val cause: Exception) : LoginResult() }
102. 3. Easier to perform different actions
103. when (response) { is LoginResult.Success -> { saveToken(response.data.accessToken) showHomeScreen() } is LoginResult.InvalidUser -> { showErrorDialog("User not valid") } //and so on… }
104. when (response) { is LoginResult.Success -> { saveToken(response.data.accessToken) showHomeScreen() } is LoginResult.ConnectionError -> { showErrorDialog("No internet connection!") } //and so on… }
105. 1. All your possible outcomes in one place 2. Helps you think of all the cases 3. Easier to perform different actions Advantages of Sealed class
106. fun login(username: String, password: String): LoginResult { return try { val response = apiCall.execute() val data = response.data if (response.isSuccessful) { if (data.authToken != null) Success(data.authToken) else InvalidUser } else { when (response.code()) { 408 -> ConnectionError 500 -> ServerError(response.errorMessage) else -> UnexpectedError(response.code()) } } } catch (error: IOException) { NetworkException(error) } }
107. Failures vs Exception
108. Failures Failure is the inability of a system to perform required function according to its specification.
110. Exception An exception occurs during the execution of a program, that disrupts the normal flow of the program's instructions.
112. sealed class LoginResult { data class Success(val data: String) : LoginResult() object InvalidUser : LoginResult() object ConnectionError : LoginResult() data class ServerError(val error: String) : LoginResult() data class UnexpectedError(val code: Int) : LoginResult() class NetworkException(val cause: Exception) : LoginResult() }
113. sealed class LoginResult { data class Success(val data: String): LoginResult() object InvalidUser: LoginResult() object ConnectionError: LoginResult() data class ServerError(val error: String): LoginResult() data class UnexpectedError(val code: Int): LoginResult() }
114. sealed class ApiExceptions(val cause: Throwable) { class NetworkRelated(cause: Throwable): ApiExceptions(cause) class Unexpected(cause: Throwable): NetworkExceptions(cause) class Unauthorised(cause: Throwable): NetworkExceptions(cause) }
115. sealed class ApiExceptions(val cause: Throwable) { class NetworkRelated(cause: Throwable): ApiExceptions(cause) class Unexpected(cause: Throwable): ApiExceptions(cause) class Unauthorised(cause: Throwable): ApiExceptions(cause) }
116. sealed class ApiExceptions(val cause: Throwable) { class NetworkRelated(cause: Throwable): ApiExceptions(cause) class Unexpected(cause: Throwable): ApiExceptions(cause) class Unauthorised(cause: Throwable): ApiExceptions(cause) }
117. Life Lesson #1
118. FAILURE is not opposite of SUCCESS It’s part of success
119. No search results
120. Whaaaat??
121. How did we get here?
126. override fun onCreate(savedInstanceState: Bundle?) { ... searchButton.setOnClickListener { val searchString = editTextView.text.toString() searchMovie(searchString) } }
127. override fun onCreate(savedInstanceState: Bundle?) { ... searchButton.setOnClickListener { val searchString = editTextView.text.toString() searchMovie(searchString) } }
128. override fun onCreate(savedInstanceState: Bundle?) { ... searchButton.setOnClickListener { val searchString = editTextView.text.toString() searchMovie(searchString) } }
129. Dig deeper!
130. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
131. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
132. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
133. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
134. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
135. fun searchMovie(movieTitle: String) { //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
136. No search results
137. fun searchMovie(movieTitle: String) { showLoadingBar() //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
138. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
139. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess() .onError() //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
140. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> //TODO Hide loading bar //TODO Show movie results } .onError() //TODO Hide loading bar //TODO Show error }
141. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError() //TODO Hide loading bar //TODO Show error }
142. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> //TODO Hide loading bar //TODO Show error } }
143. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
144. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
145. Everything works!
146. Somebody saw… A cool new feature
147. Pull to Refresh
150. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
151. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
152. Possible problem
153. Business logic mixed with UI
155. fun refresh(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
156. fun refresh(movieTitle: String) { showRefreshIcon() search(movieTitle) .onSuccess { data: List<Movie> -> hideRefreshIcon() showData(data) } .onError { error: String -> hideRefreshIcon() showError(error) } }
158. What if…
159. We sort movies by release date
160. fun searchMovie(movieTitle: String) { hideError() showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() val sortedData = data.sortedBy { it.date } showData(sortedData) } .onError { error: String -> hideLoadingBar() showError(error) } }
161. Forgetting something?
162. What about refresh() ?
163. Possible problem
164. Even small changes become hard
165. fun refresh(movieTitle: String) { showRefreshIcon() search(movieTitle) .onSuccess { data: List<Movie> -> hideRefreshIcon() val sortedData = data.sortedBy { it.date } showData(sortedData) } .onError { error: String -> hideRefreshIcon() showError(error) } }
166. No search results
167. No search results
168. fun searchMovie(movieTitle: String) { showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
169. fun searchMovie(movieTitle: String) { hideError() showLoadingBar() search(movieTitle) .onSuccess { data: List<Movie> -> hideLoadingBar() showData(data) } .onError { error: String -> hideLoadingBar() showError(error) } }
170. Possible problem
171. Unpredictable UI state
172. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
173. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
174. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
175. What is this “state” ?
180. User Events UI State
181. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
182. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar -> View state //TODO Search movie name from IMDb //TODO Hide loading bar -> View state //TODO Show movie results -> View state //TODO Show error -> View state }
183. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar -> View state //TODO Search movie name from IMDb //TODO Hide loading bar -> View state //TODO Show movie results -> View state //TODO Show error -> View state }
184. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar -> View state //TODO Search movie name from IMDb -> Action/Logic //TODO Hide loading bar -> View state //TODO Show movie results -> View state //TODO Show error -> View state }
185. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar //TODO Search movie name from IMDb //TODO Hide loading bar //TODO Show movie results or, //TODO Show error }
186. object SearchInput : UserEvent data class SearchClicked(val searchText: String) : UserEvent data class PulledToRefresh(val searchText: String) : UserEvent
187. object SearchInput : UserEvent data class SearchClicked(val searchText: String) : UserEvent data class PulledToRefresh(val searchText: String) : UserEvent
188. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading/refresh bar -> View state //TODO Search movie name from IMDb //TODO Hide loading/refresh bar -> View state //TODO Show movie results -> View state //TODO Show error -> View state }
189. data class SearchViewState( val showLoader: Boolean = false, val showRefresh: Boolean = false, val movies: List<Movie> = emptyList(), val error: String = "" )
190. data class SearchViewState( val showLoader: Boolean = false, val showRefresh: Boolean = false, val movies: List<Movie> = emptyList(), val error: String = "" )
191. fun searchMovie() { //TODO Read movie name -> UserEvents //TODO Handle search button clicks -> UserEvents //TODO Show loading bar -> Search View changes //TODO Search movie name from IMDb -> Action/Logic //TODO Hide loading bar -> Search View changes //TODO Show movie results -> Search View changes //TODO Show error -> Search View changes }
192. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> TODO() is PulledToRefresh -> TODO() } }
193. searchButton.setOnClickListener { actionOnEvent(SearchButtonClicked) } refreshLayout.setOnRefreshListener { actionOnEvent(PulledToRefresh) }
194. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> //TODO Show loader //TODO Search is PulledToRefresh -> //TODO Show refresh //TODO Search } }
195. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) //TODO Search } is PulledToRefresh -> //TODO Show refresh //TODO Search } }
196. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) render(searchAction(event.searchText)) } is PulledToRefresh -> //TODO Show refresh //TODO Search } }
197. searchButton.setOnClickListener { actionOnEvent(SearchButtonClicked) } refreshLayout.setOnRefreshListener { actionOnEvent(PulledToRefresh) }
198. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) render(searchAction(event.searchText)) } is PulledToRefresh -> //TODO Show refresh //TODO Search } }
199. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) render(searchAction(event.searchText)) } is PulledToRefresh -> render(SearchViewState(showRefresh = true)) //TODO Search } }
200. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) render(searchAction(event.searchText)) } is PulledToRefresh -> { render(SearchViewState(showRefresh = true)) render(searchAction(event.searchText)) } } }
201. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess( { data: List<Movie> -> SearchViewState(movies = data) } ) .onError( { error: String -> SearchViewState(error = error) } ) }
202. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess( { data: List<Movie> -> SearchViewState(movies = data) } ) .onError( { error: String -> SearchViewState(error = error) } ) }
203. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess( { data: List<Movie> -> SearchViewState(movies = data) } ) .onError( { error: String -> SearchViewState(error = error) } ) }
204. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess( { data: List<Movie> -> SearchViewState(movies = data) } ) .onError( { error: String -> SearchViewState(error = error) } ) }
205. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true)) render(searchAction(event.searchText)) } is PulledToRefresh -> { render(SearchViewState(showRefresh = true)) render(searchAction(event.searchText)) } } }
206. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
207. fun render(state: SearchViewState){ if(state.showLoader) { showLoadingBar() } else if(state.movies.isNotEmpty()){ showData(state.movies) } else if(state.error.isNotBlank()){ showError(state.error) } else if(state.showRefresh){ showRefreshIcon() } }
208. fun render(state: SearchViewState){ if(state.showLoader) { showLoadingBar() } else if(state.movies.isNotEmpty()){ showData(state.movies) } else if(state.error.isNotBlank()){ showError(state.error) } else if(state.showRefresh){ showRefreshIcon() } }
209. fun render(state: SearchViewState){ if(state.showLoader) { showLoadingBar() } else if(state.movies.isNotEmpty()){ showData(state.movies) } else if(state.error.isNotBlank()){ showError(state.error) } else if(state.showRefresh){ showRefreshIcon() } }
211. Forgot to hide loader? !
212. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess { data: List<Movie> -> SearchViewState(movies = data)} .onError { error: String -> SearchViewState(error = error) } }
213. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess { data: List<Movie> -> SearchViewState(movies = data, showLoader = false)} .onError { error: String -> SearchViewState(error = error) } }
214. fun render(state: SearchViewState){ if(state.showLoader) { showLoadingBar() } else if(state.movies.isNotEmpty() && !state.showLoader) { showData(state.movies) hideLoadingBar() } else if(state.error.isNotBlank()){ showError(state.error) } else if(state.pullToRefresh){ showRefreshIcon() } }
215. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
216. Possible problem • Still Business logic mixed with UI • Hard to update/maintain code • Still Unpredictable UI states
217. SearchViewState(showLoader = true, error = null) SearchViewState(showLoader = false, movies = data) SearchViewState(showLoader = false, error = error, showRefresh = false) SearchViewState(showRefresh = true)
218. Sealed classes to the rescue again!
219. data class SearchViewState( val showLoader: Boolean = false, val showRefresh: Boolean = false, val movies: List<Movie> = emptyList(), val error: String = "" )
220. Explicit is better than implicit!
221. sealed class SearchViewState { object LoadingState : SearchViewState() object PullToRefreshState : SearchViewState() data class ErrorState(val error: String) : SearchViewState() data class DataState(val movies: List<Movie>) : SearchViewState() }
222. sealed class SearchViewState { object LoadingState : SearchViewState() object PullToRefreshState : SearchViewState() data class ErrorState(val error: String) : SearchViewState() data class DataState(val movies: List<Movie>) : SearchViewState() }
223. sealed class SearchViewState { object LoadingState : SearchViewState() object PullToRefreshState : SearchViewState() data class ErrorState(val error: String) : SearchViewState() data class DataState(val movies: List<Movie>) : SearchViewState() }
224. sealed class SearchViewState { object LoadingState : SearchViewState() object PullToRefreshState : SearchViewState() data class ErrorState(val error: String) : SearchViewState() data class DataState(val movies: List<Movie>) : SearchViewState() }
225. sealed class SearchViewState { object LoadingState : SearchViewState() object PullToRefreshState : SearchViewState() data class ErrorState(val error: String) : SearchViewState() data class DataState(val movies: List<Movie>) : SearchViewState() }
226. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess { data: List<Movie> -> SearchViewState( movies = data, showLoader = false ) } .onError { error: String -> SearchViewState( showLoader = false, error = error, showRefresh = false ) } }
227. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess { data: List<Movie> -> SearchViewState.DataState(data) } .onError { error: String -> SearchViewState.ErrorState(error) } }
228. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState(showLoader = true, error = null)) render(searchAction(event.searchText)) } is PulledToRefresh -> { render(SearchViewState(showRefresh = true)) render(searchAction(event.searchText)) } } }
229. fun actionOnEvent(event: UserEvent) { when (event) { is SearchButtonClicked -> { render(SearchViewState.LoadingState) render(searchAction(event.searchText)) } is PulledToRefresh -> { render(SearchViewState.PullToRefreshState) render(searchAction(event.searchText)) } } }
230. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Still Unpredictable UI states
231. fun render(state: SearchViewState){ if(state.showLoader && state.error.isBlank()) { showLoadingBar() hideError() } else if(state.movies.isNotEmpty() && !state.showLoader) { showData(state.movies) hideLoadingBar() } else if(state.error.isNotBlank() && !state.showLoader && !state.showRefresh){ showError(state.error) hideLoadingBar() hideRefreshIcon() } else if(state.showRefresh){ showRefreshIcon() } }
232. fun render(state: SearchViewState) { when (state) { LoadingState -> showLoadingState() PullToRefreshState -> showRefreshState() is DataState -> showDataState(state.movies) is ErrorState -> showErrorState(state.error) } }
233. Possible problem • Business logic mixed with UI • Hard to update/maintain code • Unpredictable UI states
234. Advantages of Sealed class
235. 1. Mutually exclusive states (Loose coupling)
236. fun searchAction(searchText: String): SearchViewState { return search(searchText) .onSuccess { data: List<Movie> -> SearchViewState.DataState(data) } .onError { error: String -> SearchViewState.ErrorState(error) } }
237. 2. Keep similar and related things together (High Cohesion)
238. fun render(state: SearchViewState) { when (state) { LoadingState -> showLoadingState() PullToRefreshState -> showRefreshState() is DataState -> showDataState(state.movies) is ErrorState -> showErrorState(state.error) } }
239. 1. All your possible outcomes in one place 2. Helps you think of all the cases 3. Easier to perform different actions 4. Mutually exclusive states 5. Keep similar and related things together Advantages of Sealed class
240. Life lesson #2
242. Life lesson #2 const val change = "undefined"
243. Fin.
244. Twitter: @sanchita_ag