Android MVVM Architecture Sample (ViewModel + LiveData + Kotlin + Retrofit) - Weather App

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 Dagger, Coroutine or Rx in this project. After completion of this repository, if you want to learn about Dagger implementation; please check this repository for MVVM and Dagger implementation.

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.

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. We find most of the MVVM tutorials are covered with Rx and Dagger. But it's not mandatory to use Rx or Dagger in MVVM. Even without using LiveData you can implement MVVM architecture. The main difference between MVP and MVVM is: Presenter is not Life Cycle aware. On the otherhand ViewModel is Life Cycle aware.

For simplicity, I've ignored reactive programming concept (Rx) and dependency injection in this project. I have created another repository of MVVM with dependency injection Dagger 2. In future I will create another repository with Rx.