# Android Architecture Showcase

A single runnable **Android-only (Jetpack Compose)** reference app that demonstrates good
architecture conventions — each in its own module/example. Teaching repo: every module is meant to
be minimal but complete and idiomatic.

> **Status:** built milestone-by-milestone from the
> [Linear backlog](https://linear.app/adrian-kuta/project/android-architecture-showcase-b5ecdeddda6c).
> **Foundation**, **Core Infrastructure**, the **Flagship MVI** characters feature, and
> **Breadth & Contrast** (character detail, the MVVM About screen, the Views renderer, and
> Compose↔View interop) are complete and the project assembles green. Full architecture docs land
> with the *Quality & Docs* milestone.

## Stack

Multi-module Gradle + `build-logic` convention plugins · Koin (constructor DSL) · Ktor ·
KotlinX Serialization · Coil · Timber · type-safe Compose Navigation. Data comes from the no-key
[Rick & Morty API](https://rickandmortyapi.com/).

What it showcases: **MVI** as the primary presentation pattern (flagship *characters* feature),
an **MVVM** contrast screen (*about*), and the same MVI `ViewModel` driven by **two renderers** —
Jetpack Compose and classic **XML + ViewBinding + RecyclerView** — proving the presentation logic is
UI-toolkit-agnostic. See [Presentation patterns](#presentation-patterns-mvi-vs-mvvm) below.

## Module structure

```
:app                                  → wires everything; single Activity, Compose host
:build-logic                          → Gradle convention plugins (the only place versions/config live)
:core:domain                          → Result/error types, shared domain models  (pure Kotlin)
:core:data                            → Ktor HttpClient factory, safe-call helpers
:core:presentation                    → UiText, ObserveAsEvents, DataError → UiText
:core:design-system                   → AppTheme + reusable composables
:feature:characters:domain            → models + repository interface  (pure Kotlin)
:feature:characters:data              → DTOs, mappers, data source, repository impl
:feature:characters:presentation      → MVI ViewModel/State/Action/Event  (UI-agnostic: no Compose, no Views)
:feature:characters:presentation-compose → Compose renderer
:feature:characters:presentation-views   → Views/XML renderer (same ViewModel)
:feature:about:presentation           → MVVM contrast screen
```

**Dependency rules:** `presentation → domain ← data`; `domain` depends only on `:core:domain`;
features never depend on other features; `:app` wires the graph.

## Presentation patterns (MVI vs MVVM)

Both patterns live side by side so the trade-off is concrete, not theoretical.

| | **MVI** (`:feature:characters:*`) | **MVVM** (`:feature:about:presentation`) |
|---|---|---|
| State | one immutable `State` data class | one immutable `State` data class |
| User input | a single `onAction(Action)` funnel + sealed `Action` | plain public methods on the `ViewModel` |
| Side effects | one-time `Event`s via a `Channel` (nav, snackbar) | none — the screen calls a method / uses `LocalUriHandler` directly |
| Best when | state is complex and interacting; effects matter | the screen is small and mostly static |

The flagship characters list is MVI because its state is genuinely complex — pagination, loading
vs. next-page loading, error surfacing, and `SavedStateHandle` restore after process death — and it
emits navigation/snackbar effects. The About screen is deliberately MVVM: a `StateFlow` plus a couple
of public methods, with **no `Action` and no `Event` types at all**, because that ceremony would be
pure overhead for static content. Rule of thumb: **reach for MVI when state is complex and side
effects matter; reach for MVVM when the screen is simple.**

### One ViewModel, two renderers

`:feature:characters:presentation` is **UI-toolkit-agnostic** — it has no Compose *and* no Views
dependency (state stays Compose-stable via `kotlinx-collections-immutable` rather than `@Stable`).
The exact same `CharacterListViewModel` (State/Action/Event/UI-model) is rendered twice:

- `:feature:characters:presentation-compose` — Jetpack Compose (`LazyColumn`).
- `:feature:characters:presentation-views` — `Fragment` + ViewBinding + `RecyclerView`/`DiffUtil`.

`:app` hosts the Views renderer inside the Compose `NavHost` via `AndroidFragment` (Compose↔View
interop) and injects all navigation as callbacks, so the renderers stay decoupled from each other.

## Build & run

```bash
./gradlew assembleDebug     # build the APK
./gradlew projects          # print the module tree
./gradlew check             # tests + lint (added in the Quality & Docs milestone)
```

Requires JDK 17+ (the Gradle build pins a Java 17 toolchain) and the Android SDK
(`compileSdk 36`, `minSdk 24`).