Design Patterns in Kotlin

Presented at KSUG, Surat

Transcript

1. Design Patterns in Kotlin Sohel Shaikh Lead Android Engineer @ Skylark Drones
2. - 4+ YOE with Android - Lead Android Engineer @ Skylark Drones - I 💜 Kotlin! - @thesohelshaikh on Socials Hey, I am Sohel
3. A Pattern is a solution to a problem in a context.
4. A Pattern is a solution to a problem in a context. A recurring situation
5. A Pattern is a solution to a problem in a context. A recurring situation Goal in context
6. A Pattern is a solution to a problem in a context. A recurring situation Goal in context The design
7. History
8. What is it? Instead of code reuse, with patterns you get experience reuse.
9. Why bother? - Shared vocabularies - Discussions at a higher level - Tried and tested solutions - Easy to reuse
10. Singleton Pattern
11. object Keyword object Logger { fun log(line: String) { println(line) } }
12. Create Room DB instance val db = Room.databaseBuilder( applicationContext, AppDatabase-:class.java, "database-name" ).build()
13. Singleton with Params class AppDatabase { companion object { private var INSTANCE: YTDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE -: Room.databaseBuilder( context.applicationContext, AppDatabase-:class.java, "app_database" ).build().apply { INSTANCE = this } } } }
14. Singleton with Params class AppDatabase { companion object { private var INSTANCE: YTDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE -: Room.databaseBuilder( context.applicationContext, AppDatabase-:class.java, "app_database" ).build().apply { INSTANCE = this } } } }
15. Singleton with Params class AppDatabase { companion object { private var INSTANCE: YTDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE -: Room.databaseBuilder( context.applicationContext, AppDatabase-:class.java, "app_database" ).build().apply { INSTANCE = this } } } }
16. Singleton with Params (Thread safe) class AppDatabase { companion object { @Volatile private var INSTANCE: YTDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE -: synchronized(this) { val instance = Room.databaseBuilder( context.applicationContext, AppDatabase-:class.java, "app_database" ).build().apply { INSTANCE = instance } } } } }
17. Singleton with Params (Thread safe) class AppDatabase { companion object { @Volatile private var INSTANCE: YTDatabase? = null fun getDatabase(context: Context): AppDatabase { return INSTANCE -: synchronized(this) { val instance = Room.databaseBuilder( context.applicationContext, AppDatabase-:class.java, "app_database" ).build().apply { INSTANCE = instance } } } } }
18. Singleton with Params (Thread safe) class MyApplication : Application() { val database by lazy { AppDatabase.getDatabase(this) } }
19. An Anti-Pattern tells you how to go from a problem to BAD Solution.
20. Singleton Cons - Creates Global state - Hard to debug - Hard to test - Hides a complex design flaw - Thread safety handling
21. Observer Pattern aka Pub-Sub Pattern aka Event Bus
22. java.util
24. class KotlinNewsLetter { val newestArticleObservers = mutableListOf<KotlinDeveloper>() var newestArticleUrl: String by Delegates.observable("") { _, _, newValue -> newestArticleObservers.forEach { it.read(newValue) } } } Kotlin Delegates
25. class KotlinNewsLetter { val newestArticleObservers = mutableListOf<KotlinDeveloper>() var newestArticleUrl: String by Delegates.observable("") { _, _, newValue -> newestArticleObservers.forEach { it.read(newValue) } } } Kotlin Delegates
26. class KotlinNewsLetter { val newestArticleObservers = mutableListOf<KotlinDeveloper>() var newestArticleUrl: String by Delegates.observable("") { _, _, newValue -> newestArticleObservers.forEach { it.read(newValue) } } } class KotlinDeveloper { fun read(article: String) { println("$this Reading $article") } } Kotlin Delegates
27. val newsLetter = KotlinNewsLetter() val developerAlpha = KotlinDeveloper() val developerBeta = KotlinDeveloper() newsLetter.newestArticleObservers.add(developerAlpha) newsLetter.newestArticleObservers.add(developerBeta) newsLetter.newestArticleUrl = "www.kotlin.com" newsLetter.newestArticleUrl = "www.java-is-bad.com"
29. Factory Pattern enum class ExportFormat{ Csv, Pdf } interface Exporter { fun export(): File } class CsvExporter: Exporter { override fun export(): File { --. } } class PdfExporter: Exporter { override fun export(): File { --. } }
30. Factory Pattern class ExporterFactory { companion object { fun create(format: ExportFormat): Exporter { return when(format) { ExportFormat.Csv -> CsvExporter() ExportFormat.Pdf -> PdfExporter() } } } }
31. Factory Pattern val exporter = ExporterFactory.create(ExportFormat.Csv) val file = exporter.export()
32. Factory Pattern with different constructor parameters?
33. Sealed Classes
35. Memento Pattern Use the Memento Pattern when you need to be able to return an object to one of its previous states; for instance, if your user requests an “undo.”
36. UML class diagram of Memento pattern
37. Design Principle Identify the aspects of your application that vary and separate them from what stays the same.
38. Abstraction of Video broadcasting functionality
39. Design Principle Program to an interface, not an implementation.
40. Abstraction of event tracking mechanism
41. Be Cautious! - Another tool in the toolbox - Hard to refactor later - Focus on the problem
42. Modern Recommendations
43. Unlocking the economic potential of the skies We’re Hiring! Skylark Drones
44. What are your questions? Too shy? Ping me @thesohelshaikh
45. Thank you!