Android Weather App with Retrofit

Project roadmap

1. 01

   Set up the project and networking

   ~2h

   Create an Android project with Jetpack Compose (Empty Activity template). Add Retrofit with the kotlinx.serialization (or Moshi) converter, and the INTERNET permission. Define two Retrofit interfaces: the Open-Meteo geocoding API (search a city, returns coordinates) and the forecast API (current conditions plus 5 daily min and max temperatures and weather codes). Create @Serializable data classes for the responses. Done when: a quick test call logs the forecast for a city.

2. 02

   Write the repository

   ~1.5h

   Create a WeatherRepository with a suspend function getWeather(city) that looks up the coordinates, fetches the forecast and maps both into your own domain model (CityWeather with the current conditions and a list of DailyForecast), converting weather codes into a description and an icon. Return a Result: CityNotFound, a network error, or success. Done when: the repository returns a CityWeather for a real city and CityNotFound for a made-up one.

3. 03

   Manage state in a ViewModel

   ~2h

   Create a WeatherViewModel exposing a StateFlow<WeatherUiState> with the states Idle, Loading, Success(data) and Error(message). The search(city) function trims the input, ignores empty searches, sets Loading, and calls the repository in viewModelScope. Cancel a previous search when a new one starts. Done when: calling search moves the state through Loading to Success or Error.

4. 04

   Build the search and results screens

   ~2.5h

   Build the Compose UI: a search field with a search button (and search from the keyboard's action), a spinner for Loading, a card with the current conditions for Success, and a LazyColumn (or LazyRow) of 5 daily forecast cards with the day name, icon, min and max. Collect the state with collectAsStateWithLifecycle. Done when: searching a city shows its current weather and 5-day forecast.

5. 05

   Handle errors and cache the last result

   ~2h

   Show clear messages for city not found, no internet and server errors, with a Retry button. Save the last successful result as JSON in DataStore and show it on startup, labeled with the time it was fetched, so the app is useful offline. Done when: turning on airplane mode after a search shows the cached weather with its time and a no-connection message.

6. 06

   Write tests

   ~2h

   Write unit tests for the ViewModel with a fake repository and kotlinx-coroutines-test: a successful search, city not found, a network error and ignoring empty input. Test the repository's mapping with a JSON response saved as a test resource and MockWebServer. Done when: ./gradlew test passes.

Resources

• DocsJetpack Compose tutorial
• DocsRetrofit
• DocsOpen-Meteo forecast API
• DocsGuide to app architecture (Android)
• DocsKotlin coroutines on Android