Banger

A modern, modular Android wallpaper app built with Jetpack Compose, Kotlin, and Clean-ish feature modularization. It lets users browse wallpaper categories, view wallpaper details, explore authors, save favourites, and customize app theme preferences.

Table of Contents

• Overview
• Key Features
• Tech Stack
• Project Architecture
  • High-Level Module Map
  • Layer Responsibilities
  • Dependency Injection Graph
  • Navigation Architecture
  • Data Flow
• Modules
• Screenshots
• Getting Started
  • Prerequisites
  • Setup
  • Build and Run
• Quality and Tooling
• Notes

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Overview

Banger is a multi-module Android app that integrates with the Unsplash API to serve wallpaper content. The app uses:

• A feature-first module structure (feature/*) for UI + use cases per screen area.
• data:remote for network concerns (Retrofit, OkHttp, serialization).
• data:local for Room persistence and DataStore-backed settings.
• Koin for dependency injection and Compose Navigation for routing.

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Key Features

• Browse curated wallpaper categories from Home.
• Open category-specific wallpaper feeds.
• View wallpaper details and related metadata.
• Browse authors and inspect author profile/details.
• Save and view favourite wallpapers.
• Configure app theme (system / light / dark).

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Tech Stack

• Language: Kotlin
• UI: Jetpack Compose + Material 3
• Navigation: Navigation Compose (typed routes with Kotlin serialization)
• DI: Koin
• Networking: Retrofit + OkHttp + kotlinx.serialization
• Image Loading: Coil 3
• Local Storage:
  • Room (cached photos, metadata, favourites)
  • DataStore Preferences (theme settings)
• Build: Gradle (Kotlin/Android plugin aliases via Version Catalog)
• Static Checks: ktlint configured at root and aggregated across modules

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Project Architecture

High-Level Module Map

app (entrypoint, nav host, app scaffolding)
├── feature:home
├── feature:details
├── feature:favourites
├── feature:author
├── feature:author_details
├── feature:settings
├── shared:theme
├── shared:utility
├── data:remote
└── data:local

Layer Responsibilities

This project is organized by feature, where each feature commonly contains:

• ui/ → Compose screens + ViewModels
• domain/ → repository contracts/implementations + use-case logic
• di/ → Koin module bindings for that feature

Supporting shared/data modules:

• data:remote → Retrofit setup, OkHttp interceptors, API constants/models.
• data:local → Room database, DAO, entities, and DataStore-based settings repo.
• shared:theme → app theme, reusable UI components, resources.
• shared:utility → utility helpers like blur hash decoding.

Dependency Injection Graph

The app initializes Koin in WallpaperDownloaderApplication and registers modules from app/data/features.

Core idea:

1. remoteModule provides Retrofit, OkHttpClient, JSON parser.
2. localModule provides WDDatabase, WDDao, SettingsRepository.
3. Each feature module requests only what it needs (e.g., Retrofit, WDDao, dispatchers) and exposes ViewModel + repository bindings.

This keeps feature concerns isolated and testable.

Navigation Architecture

MainActivity hosts a single NavHost with typed destinations (AppDestinations) and a bottom bar for:

• Home
• Favourites
• Authors

Additional routes:

• Category Details
• Wallpaper Details
• Settings
• Author Details

Navigation uses serialized route data classes, allowing strongly typed arguments like Details(id) and AuthorDetails(username).

Data Flow

A typical flow (example: category photos):

1. UI triggers ViewModel action.
2. ViewModel calls repository/use-case.
3. Repository fetches remote data via Retrofit.
4. Repository caches/reads entities via Room DAO.
5. UI collects Flow/State and recomposes.

Theme flow:

1. MainViewModel collects theme from SettingsRepository (DataStore).
2. App theme updates in MainActivity and recomposes globally.

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Modules

app

• Application class starts Koin and wires all modules.
• MainActivity owns app-wide scaffold + bottom navigation + route graph.
• MainViewModel exposes app theme state from local settings.

feature:home

• Category landing screen and category wallpaper listing.
• Home repository handles both network retrieval and category-based local cache stream.
• Includes HomeUseCase for concurrently requesting multiple sections.

feature:details

• Wallpaper detail screen.
• Fetches expanded item details and supports detail actions.

feature:favourites

• Favourite wallpapers list and interactions.
• Backed by local storage layer for persisted favourite state.

feature:author

• Author listing and navigation to author details.

feature:author_details

• Author profile/details screen and related author images.

feature:settings

• Settings UI, including theme preference management.

data:remote

• Retrofit base URL: https://api.unsplash.com/
• Adds Unsplash client_id via OkHttp interceptor using BuildConfig.ACCESS_KEY.
• Configures JSON parser and logging interceptor.

data:local

• Room database (WDDatabase) with migration history.
• Entities for photos, users, urls, links, profile images.
• DataStore settings repository for app theme preference.

shared:theme

• Compose theme and reusable UI components.
• Centralized colors, typography, shapes, and drawable resources.

shared:utility

• Utility helpers (e.g., blur hash decoder).

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Screenshots

Below are project screenshots pulled from the screenshots/ folder in the repository root.

App Preview Gallery

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Getting Started

Prerequisites

• Android Studio (recent stable)
• Android SDK (compile/target SDK 35)
• JDK 11
• Unsplash access key

Setup

1. Clone the repository.
2. Create a local.properties file in project root if missing.
3. Add your Unsplash key:

ACCESS_KEY=your_unsplash_access_key_here

The key is injected through Gradle into BuildConfig.ACCESS_KEY for modules that apply the shared build logic.

Build and Run

Use Android Studio Run, or CLI:

./gradlew :app:assembleDebug
./gradlew :app:installDebug

Optional quality checks:

./gradlew ktlintCheck
./gradlew test

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Quality and Tooling

• ktlint is applied across subprojects and aggregated into root tasks.
• Multi-module structure improves build isolation and ownership.
• Room schema is exported under data/local/schemas/ for migration visibility.

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Notes

• Project name in Gradle: Banger.
• Minimum SDK is 24.
• The repository currently stores screenshots in screenshots/ and this README links directly to those assets.