5-Layer MVVM Keeps SwiftUI Apps Maintainable
Implement MVVM as five layers—Models, Repositories, Services, ViewModels, Views—to isolate UI from data, logic, and persistence, enabling dependency injection and isolated ViewModel testing.
Layered MVVM Separates Concerns for Scalability
Build SwiftUI apps using a 'full layer cake' MVVM with five distinct layers to prevent Views from handling data or logic, resulting in boring, maintainable code. Models define pure data structures like Task (with title, notes, priority, category, due date, completion status), SubTask, TaskPriority (Low/Medium/High), and TaskCategory—no UI or persistence code. Repositories abstract storage via protocols like TaskRepositoryProtocol; TaskRepository uses SwiftData's ModelContext but hides it from callers. Services handle cross-cutting utilities: date checks (e.g., 'is this today?'), greeting generation, formatting, settings, and notifications, avoiding bloated ViewModels. ViewModels (@Observable) manage screen state, fetch via repositories, process with services, and expose UI-ready data/actions. Views render only, calling ViewModel methods without business rules.
This structure scales by keeping each layer single-responsibility: Views stay declarative, ViewModels testable, and data/persistence swappable.
Dependency Injection and Data Flow Enable Testing
Inject repositories and services at app launch via @Environment or root views—ViewModels never instantiate dependencies. Data flows unidirectionally: user actions trigger ViewModel methods (e.g., toggleComplete(task)), which call repository.toggleComplete(task) updating ModelContext, then refresh observable state for Views. Protocols like TaskRepositoryProtocol allow faking for unit tests: swap FakeTaskRepository to test ViewModels without SwiftData, UI, or real persistence, verifying state changes and actions in isolation.
Trade-off: Adds upfront boilerplate but prevents God objects and eases refactoring as apps grow.
Demo App Features Validate Architecture
The todo app showcases layers across screens. Today view displays due-today tasks with progress ring and personalized greeting (via Services). All Tasks lists with filters (All/Active/Completed, by category) loaded by ViewModel. Add Task form sets priority/category/due date/time/subtasks. Search queries tasks by name, showing matches with details. Settings manages profile, default priority, theme (System/Light/Dark), notifications—all persisted via repository. UI uses Liquid Glass effects for polish. Run by opening IOSMvvCApp.xcodeproj in Xcode; MIT licensed.