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UIApp

News reader UI that fetches articles from BackendApp's ContentProvider via IPC. Built with Jetpack Compose (MVVM), Hilt for DI, and Coil for image loading.

Prerequisites

BackendApp must be installed before running UIApp. The ContentProvider authority com.unity.backendapp.provider is resolved at the system level — if BackendApp isn't installed, ContentResolver.query() returns null and the user sees an error.

Both APKs must be signed with the same key so that UIApp can hold BackendApp's signature-protected read permission. Debug builds from the same machine satisfy this automatically.

Build

Requires JDK 17+ and the Android SDK. Android Studio (Ladybug or newer) resolves both automatically; from the command line, point JAVA_HOME at a JDK 17+ if your shell default is older.

cd UIApp
./gradlew assembleDebug

APK at app/build/outputs/apk/debug/app-debug.apk.

Install

adb install app/build/outputs/apk/debug/app-debug.apk

Usage

  1. Launch the app.
  2. Articles load automatically from BackendApp via ContentProvider IPC.
  3. Search field — filter by title (case-insensitive substring match).
  4. Rating slider — set minimum rating (1–5, discrete steps).
  5. Apply Filters button — sends the filter to BackendApp.
  6. If no articles match, a "No articles found" message is shown.
  7. If the backend is unreachable, an error message is shown (distinct from "no matches").

Verify it's talking to BackendApp

Quick check — article count

The bundled dataset has 129 articles. If the list shows 129 items on first launch with no filters, IPC is working.

Kill BackendApp and re-verify

  1. Force-stop BackendApp from Settings → Apps → BackendApp → Force Stop.
  2. In UIApp, tap "Apply Filters" with no filter changes.
  3. Articles should still load — Android re-creates the ContentProvider on demand (Room DB persists on disk).

ADB verification

adb shell dumpsys package com.unity.backendapp | grep provider

You should see com.unity.backendapp.provider listed as an exported provider.

Check for errors

If the screen stays on "Loading..." indefinitely, BackendApp is not installed or the provider is blocked. On Android 11+ devices, verify that UIApp's manifest includes:

<queries>
    <package android:name="com.unity.backendapp" />
</queries>

Architecture

BackendApp ContentProvider (query → Cursor)
  → ContentResolverDataSource (ContentResolver.query, cursor → List<Article>)
    → ArticleViewModel (StateFlow<ArticleUiState>)
      → ArticleListScreen (Compose) → ArticleCard
  • ArticleFilter data class: Both apps share the same filter shape. UIApp's ArticleUiState.toFilter() converts form fields to the immutable ArticleFilter that crosses the data-source boundary. Adding a new filter = add a field + one UI control — no interface or data-source signature changes.
  • ArticlesDataSource interface: Abstracts the IPC mechanism — allows testing with an in-memory fake instead of mocking the (final) ContentResolver.query() method.
  • ContentResolverDataSource: Maps a Cursor to List<Article>. Throws IOException on failure (null cursor, timeout, IPC error) so the VM can distinguish "no matches" from "backend unreachable". Column indices are cached once per query. CancellationSignal is wired to coroutine cancellation for proper timeout behavior.
  • MVVM: ArticleViewModel holds a StateFlow<ArticleUiState>. Filter params are exposed as mutable state; applyFilters() launches a coroutine on an injected @IoDispatcher and updates state on completion.
  • Concurrency protection: fetchJob?.cancel() prevents overlapping filter calls from overwriting each other out of order.
  • Hilt: @HiltViewModel, @AndroidEntryPoint, @Binds for ArticlesDataSource, @IoDispatcher qualifier for testable dispatchers.
  • Coil 2.7.x: AsyncImage for article images from network URLs, with a per-article placeholder color (from placeholderColor field) shown behind the image until it loads.
  • INTERNET permission: Required by Coil for network image loading.
  • READ_ARTICLES permission: Required to query BackendApp's provider (signature-level, auto-granted for same-key APKs).

Tests

# Unit tests — ArticleViewModel (10)
./gradlew testDebugUnitTest

# Instrumentation tests — ArticleCard Compose (3), ArticleFilterUri (5), cursor mapping (3)
./gradlew connectedDebugAndroidTest
Suite Location Tests What they cover
ArticleViewModelTest src/test 10 Loading state, filter application, title/rating filter, empty result, error state, rating clamping, error vs empty distinction
ArticleFilterUriTest src/androidTest 5 URI encoding: empty filter, title only, rating only, both, blank-title skipping
ArticleCardTest src/androidTest 3 Title/description rendered, rating number, low-rating variant
ContentResolverMappingTest src/androidTest 3 Cursor → Article mapping: all columns, empty cursor, missing-column failure

Key gotchas

  • <queries> manifest entry: Android 11+ hides BackendApp's ContentProvider from UIApp unless <queries><package android:name="com.unity.backendapp"/> is declared.
  • Signature permission: Both APKs must be signed with the same key (see Prerequisites).
  • INTERNET permission: Coil silently crashes without it.
  • Filter key parity: URI param names (titleQuery, ratingMin) in ArticleFilter companion constants must match BackendApp's ArticleFilter constants exactly — no compile-time cross-app checking. Centralized constants in both apps minimize drift.