PatternKit — MVVM (XML Views)

Part of PatternKit, a side-by-side reference codebase where the same small Tasks CRUD app is implemented once per architecture pattern across iOS and Android. Every module ships identical behaviour — the same domain model, the same three screens, the same mock data layer — so the only thing that varies is the architecture itself.

This module is the MVVM flavour on the traditional XML view stack — Fragments, the Navigation component, ViewBinding, and a RecyclerView adapter. It's the counterpart to the Compose MVVM module: identical architecture and behaviour, but rendered the way the large majority of existing production Android codebases still are. Useful as a direct before/after when reasoning about a Compose migration.

Stack

• Language: Kotlin
• UI: XML layouts + ViewBinding · Fragments · RecyclerView
• Architecture: MVVM (no domain layer)
• Navigation: Jetpack Navigation component (nav_graph.xml)
• DI: Dagger 2 (KSP) — plain Dagger, no Hilt
• Min SDK: 28 · Target/Compile SDK: 36
• Package: com.preetanshumishra.patternkit.android.mvvmxml

The Tasks feature

A single-user task list. One entity (TaskItem: title, optional notes, optional due date, priority, completion). Three screens:

1. List (TaskListFragment) — filter chips (All / Active / Completed), sort by due date or priority, swipe-to-delete via RecyclerView, FAB to create.
2. Detail (TaskDetailFragment) — read-only fields, toggle completion, edit, delete.
3. Form (TaskFormFragment) — create or edit (mode-driven), title validation (≤ 80 chars), due-date validation (not in the past), 600 ms mock async save.

Data comes from MockTaskRepository — an in-memory store seeded with ~12 tasks, with configurable artificial latency and failure rate. No real network, no local persistence — intentionally, so the architecture stays the focus.

XML-stack specifics

• Fragments + Navigation component — screens are Fragments wired through res/navigation/nav_graph.xml; arguments are passed via a small NavArgs helper.
• ViewBinding — type-safe view access, no findViewById.
• RecyclerView + TaskAdapter — list rendering with a diffing adapter.
• Event wrapper — one-shot UI events (navigation, errors) exposed from the ViewModel without re-firing on configuration change.

Dependency injection

Plain Dagger 2, wired by hand:

• AppComponent (@Singleton) exposes the repository; RepositoryModule @Binds TaskRepository → MockTaskRepository.
• PatternKitApp creates and holds the component; a hand-rolled ViewModelFactory constructs each ViewModel from the repository in the graph.

Project layout

app/src/main/
├── kotlin/.../mvvmxml/
│   ├── data/        # MockTaskRepository, TaskRepository, seed data
│   ├── model/       # TaskItem, Priority, TaskFilter, TaskSort
│   ├── di/          # AppComponent, RepositoryModule
│   ├── ui/
│   │   ├── list/    # TaskListFragment + TaskAdapter + TaskListViewModel
│   │   ├── detail/  # TaskDetailFragment
│   │   ├── form/    # TaskFormFragment + TaskFormViewModel
│   │   ├── Event.kt, NavArgs.kt, MainActivity, ViewModelFactory
│   └── PatternKitApp.kt
└── res/
    ├── layout/      # activity_main, fragment_list/detail/form, item_task
    ├── menu/        # menu_list, menu_detail
    └── navigation/  # nav_graph.xml

Build & run

./gradlew assembleDebug      # build the debug APK
./gradlew installDebug       # install on a connected device/emulator
./gradlew test               # unit tests

Or open the project in Android Studio and run the app configuration.