Harnessing the Power of Kotlin Flow: Effortlessly Fetch User Location

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During my recent exploration of Kotlin Flows, I stumbled upon a fascinating feature called Kotlin callbackFlow. In this article, we will delve into the concept of callbackFlow and explore its applications in Android, particularly in emitting flows from callback implementations. Today, our focus will be on utilizing callbackFlow to fetch the user’s location. But before we dive into that, let’s take a look at the traditional approach we usually employ to retrieve the user’s location.

TL;DR — You can find the whole implementation on GitHub.

We have our GeoLocationListener.kt which is an interface that will be used for providing the location to our FetchLocationActivity.kt.

Next, we have the LocationProvider.kt which fetches the user location and provides it to our FetchLocationActivity.kt which implements the GeoLocationListener.kt interface.

Now let’s see how we will use this LocationProvider.kt in our FetchLocationActivity.kt. In our activity, we can use the Location object received in onCurrentGeoLocationSuccess(location: Location) to extract latitude and longitude.

Implementing Location Fetching with callbackFlow

In this section, we will focus on the main topic of this article, which is utilizing callbackFlow to fetch the user’s location. To achieve this, we will follow the principles of Clean Architecture and employ the MVVM (Model-View-ViewModel) design pattern. Let’s start by creating a UseCase specifically for fetching the user’s location, which we will name FetchLocationUseCase.kt.

Now we will provide the implementation for our FetchLocationUseCase.kt as FetchLocationUseCaseImpl.kt. We will be using Hilt for dependency injection and will be injecting FetchLocationUseCase in our ViewModel. Below is the implementation for FetchLocationUseCase.kt

callbackFlow is a flow builder that lets you convert callback-based APIs into flows. More information here Convert callback-based APIs to flows

Now let’s see how our ViewModel will use FetchLocationUseCase.kt to receive fetched location and later it can use this latitude and longitude for further requirements.

Do not worry if you see some extra things being done here I will share the GitHub repo for the sample project which contains all the code. Here I have used only some samples for giving a high-level idea about the implementations.

Now we have received our location in

is ResultState.Success -> { 
    val latitude = result.data.latitude 
    val longitude = result.data.longitude
    saveLatLongToSavedStateBundle(latitude, longitude)  
    fetchNearByVenues(latitude, longitude) 
}

Great! If you have followed all along. The code for this sample project can be found here on GitHub. All suggestions for improvements are welcomed. Please star the repository if you found the code useful.

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