Koin DI, Repository Pattern & ViewModel in Kotlin Compose Desktop | Lesson 16

Learn dependency injection with Koin in Kotlin Compose Desktop! We build a Book Library app from scratch with clean architecture: repository pattern, ViewModel with StateFlow, and Koin wiring it all together. Browse 18 books, search by title/author, favorite books, and view details in a split-panel layout. What You'll Learn: - Setting up Koin 4.1.1 with koin-core and koin-compose dependencies - Pinning Compose version with resolution strategy (avoiding Skiko native crash) - Repository pattern: BookRepository interface + InMemoryBookRepository implementation - ViewModel with constructor injection: LibraryViewModel takes BookRepository parameter - StateFlow for reactive UI state management (LibraryUiState data class) - Koin modules: dataModule (single) and uiModule (single with get()) - koinInject() in composables for automatic ViewModel injection - KoinApplication wrapper in Main.kt for initialization - Derived state with remember() for filtering and selection - Testing with FakeBookRepository — 7 ViewModel tests with zero infrastructure Timestamps: 0:00 - Introduction 0:15 - Preview: Architecture & Test Results 0:45 - Project Setup (Gradle with Koin Dependencies) 2:49 - Models & Repository (BookModels + BookRepository) 5:17 - ViewModel & DI (LibraryViewModel + AppModule) 7:26 - Book Item Composable 10:19 - Book Panels (BookDetail + BookList) 16:35 - App Content & Main + Compile 19:55 - Tests (LibraryViewModelTest + Run Tests) 23:46 - Live Demo: Book Library App 24:35 - Recap & Key Takeaways 25:35 - Thanks for Watching Key Takeaways: 1. Koin Setup — koin-core + koin-compose, define modules with single { } and get() 2. Repository Pattern — Interface + implementation, swap in fakes for testing 3. ViewModel with DI — Constructor takes BookRepository, Koin resolves it automatically 4. Compose Integration — koinInject() replaces manual ViewModel creation 5. Testability — FakeBookRepository lets you test ViewModel logic with zero infrastructure Previous Lesson: Lesson 15: Testing — Weather App with JUnit4 & MockEngine https://youtube.com/... Next Lesson: Lesson 17: Packaging & Distribution (coming soon) Tech Stack: Kotlin 2.1, Compose Multiplatform 1.7.3, Material3 Koin 4.1.1 (koin-core, koin-compose) kotlinx-coroutines-test 1.9.0 Gradle 8.10, JVM 17+ Source Code: https://github.com/GoCelesteAI/kotlin_desktop_book_library Taught by CelesteAI If you found this helpful, please like and subscribe for more Kotlin Desktop tutorials! #kotlin #compose #desktop #material3 #koin #dependencyinjection #repository #viewmodel #stateflow #tutorial #programming