Android MVVM Weather App (Kotlin + Retrofit + Dagger)

MVVM Architecture is one of the most popular and latest architecture to develop a maintanable and managable codebase. We are developing a sample Weater Forecast Android App with MVVM Architecture using Kotlin language and Retrofit network calling library. For simplification, I didn't use Coroutine or Rx in this project. My main focus is to implement MVVM and Dagger 2 dependency injection library as simple as possible.

If you are not familiar with MVVM architecture, then I recommend you to check this MVVM respository with same Weather App project. In that project, you'll find simple MVVM implementation without Dagger. After completion of that project, you can continue this repository.

Same weather app project is available for Flutter in this repository.

Prerequisites

Basic Kotlin and knowledge of HTTP request by Retrofit library are required for this project. If you already know MVP Architecture then this project will be very easy to understand. You can check my MVP Architecture Weather App repository from here. It will be helpful if you cover the MVP project then compare between MVP and MVVM. There is my another repository where I've implemented same weather App in MVVM architecture without Dagger.

Project Description

We will develop a weather forecast Android Application with MVP architecture. The UI will be as like as above screenshot. There is a Spinner with some City name. After selection a city user need to hit the View Weather button. Then App will send request to Open Weather web API and show the weather information in the UI.

Open Weather API

We will use Open Weather Map API for collecting weather information. To get the real weather information of a city, you need to sign up and get your own APP ID. Otherwise you can test the API with their sample BASE URL and sample APP ID without creating account.

Project Setup

Clone the project and open it using Android Studio. Then open your local.properties file under Gradle Scripts. You need to specify the base_url and app_id in your local.properties file. Store your API secret in plain string file or Kotlin file is very risky. For security purpose it's better store in local.properties file than plain string/Kotlin file.

Use Sample API without creating account

Add below lines at the end of your local.properties file. Then run the project. You'll get dummy or static API response from Open Weather API.

#this is sample Base URL
base_url=https://samples.openweathermap.org/data/2.5/

#this is sample App ID of Open Weather API
app_id=b6907d289e10d714a6e88b30761fae22

Use Real APP ID after sign up and activation of your APP ID

After Sign up at the website collect your own APP ID from their API Keys page. Then add below lines with your APP ID at the end of local.properties file.

#this is real Base URL
base_url=http://api.openweathermap.org/data/2.5/

#this is real App ID of Open Weather API
app_id=YOUR_OWN_APP_ID

The BASE URL and APP ID will be fetched from build.gradle file and will be stored it in BuildConfig. And Retrofit API call will use the BASE URL and APP ID from BuildConfig.

Note: The free version of Open Weather API allows maximum 60 API calls per minute.

Run the project

Sync the Gradle and run the project. Install APK on your emulator or real device. Turn on the internet of your testing device. For better understanding, please read the comments of every methods. Hope, these comments will help you to feel the MVVM Architecture.

Disclaimer

There are some other ways of implementation of MVVM. For simplicity, I've ignored RxJava in this project. I will create another repository of MVVM with Rx.