Tenky

A small Android weather app: current conditions, the next 24 hours, and a five-day forecast for your location or any city you pin.

Setup

The app needs a free OpenWeather API key. Keys are not committed — they are read from local.properties, which is git-ignored.

1. Create a free account and generate a key at openweathermap.org/api_keys.

2. Copy local.properties.example to local.properties (Android Studio usually creates the file for you with just sdk.dir).

3. Add your key:

   OPENWEATHER_API_KEY=your_api_key_here

4. Build and run.

A new key can take around ten minutes to activate. Until then the API returns 401 and the app shows "The OpenWeather API key was rejected".

CI can supply the key through an OPENWEATHER_API_KEY environment variable instead. If neither is set the project still builds, and the app shows a "no API key configured" message rather than failing at compile time.

Note on client-side keys. The key is injected into BuildConfig at build time, which keeps it out of version control but not out of the APK — anyone can extract it from a shipped binary. That is inherent to calling a third party API directly from a mobile client. Hiding it properly would require proxying requests through a backend you control.

Which OpenWeather endpoints this uses

Endpoint	Purpose
data/2.5/weather	Current conditions
data/2.5/forecast	Five-day forecast in three-hour steps
geo/1.0/direct	City search / geocoding

All three are on the free tier. The app deliberately avoids One Call: version 2.5 was switched off in June 2024, and version 3.0 requires a separate paid "One Call by Call" subscription. Both return HTTP 401 on a free key.

Because the free forecast endpoint returns three-hour steps over five days, the hourly strip shows three-hour intervals and the daily list covers five days, aggregated from those steps.

Architecture

Single-Activity Jetpack Compose app, roughly MVVM:

fr.dutapp.tenky
├── data
│   ├── remote      Retrofit service, DTOs, API-key interceptor
│   ├── local       DataStore: settings, saved cities, selected place
│   ├── WeatherMappers.kt    DTO → domain, three-hourly → daily aggregation
│   └── WeatherRepository.kt Returns DataResult instead of throwing
├── domain/model    Domain types and the DataResult/WeatherError pair
├── location        LocationManager wrapper (no Play Services)
├── ui              Compose screens + ViewModels, theme, formatting
└── AppContainer.kt Hand-written dependency container

Notes on a couple of deliberate choices:

• No Play Services. Location goes through the platform LocationManager so the app works on devices without Google Play Services.
• No DI framework. AppContainer is small enough to read in one sitting and keeps annotation processing out of the build.

Development

./gradlew assembleDebug     # build
./gradlew testDebugUnitTest # unit tests
./gradlew assembleRelease   # minified release build

Requires JDK 21. Kotlin comes from AGP 9's built-in Kotlin support, so there is no org.jetbrains.kotlin.android plugin in the build files.

Languages

The app ships English, French and Korean, and offers an in-app language picker under Settings. It uses AppCompatDelegate.setApplicationLocales, so on Android 13 and later the choice is also exposed in Settings → Apps → Tenky → Language.

Adding a language means touching four places: a values-<code>/strings.xml, the AppLanguage enum, res/xml/locales_config.xml, and localeFilters in app/build.gradle.kts.

Note that OpenWeather's lang codes are not all ISO 639-1 — Korean is kr, not ko. An unrecognised code is not an error; the API just answers in English. See toOpenWeatherLanguage().

Credits

Weather icon pack by Those Icons — flaticon.com/packs/weather-76.