The open event attendee is an android app which allows users to discover events happening around the world using the Open Event Platform. It consumes the APIs of the open event server to get a list of available events and can get detailed information about them. It deals with events based on location, but we have to take the location as an input from the user. While in many cases, we have to search for events on our current location only. To make this work, I have added a current location option, where the app will get our location and search for nearby events. Earlier we had to enter our current location as well to search nearby events.

Model–view–viewmodel is a software architectural pattern. MVVM facilitates separation of development of the graphical user interface – be it via a markup language or GUI code – from the development of the business logic or back-end logic (the data model).

• Why Model-view-ViewModel?
• Setup Geo location View Model
• Configure location feature with MVVM
• Conclusion
• Resources

Let’s analyze every step in detail.

Advantages of using Model-view-ViewModel

1. A clean separation of different kinds of code should make it easier to go into one or several of those more granular and focused parts and make changes without worrying.
2. External and internal dependencies are in separate pieces of code from the parts with the core logic that you would like to test.
3. Observation of mutable live data whenever it is changed.

Setup the Geolocation view model

Created new kotlin class name GeoLocationViewModel which contains a configure function for current location:

package org.fossasia.openevent.general.search

class GeoLocationViewModel : ViewModel() {
    fun configure(activity: Activity) { }                                     
}

The GeoLocationViewModel class implement as VIewModel().

Now add the class in module inside Modules.kt :

val viewModelModule = module {
    viewModel { GeoLocationViewModel() }
}

Configure location feature with GeoLocationViewModel:

First, add play store location service implementation inside dependencies of build.gradle:

// Location Play Service
playStoreImplementation 'com.google.android.gms:play-services-location:16.0.0'

Now we need location permissions to implement this feature. Adding user permissions in the manifest file:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

Now ask user for the location permission:

private fun checkLocationPermission() {
        val permission = context?.let {
            ContextCompat.checkSelfPermission(it, Manifest.permission.ACCESS_COARSE_LOCATION) }
        if (permission != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION,
                Manifest.permission.ACCESS_FINE_LOCATION), LOCATION_PERMISSION_REQUEST)
        }
    }

Check for device location is enabled, if not send an intent to turn location on. The method is written inside configure function:

val service = activity.getSystemService(Context.LOCATION_SERVICE)
        var enabled = false
        if (service is LocationManager) enabled = service.isProviderEnabled(LocationManager.NETWORK_PROVIDER)
        if (!enabled) {
            val intent = Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS)
            activity.startActivity(intent)
            return
        }

Now create Mutable live data for current location inside the view model class :

private val mutableLocation = MutableLiveData<String>()
val location: LiveData<String> = mutableLocation

Now implement location request and location callback inside configure method:

val locationRequest: LocationRequest = LocationRequest.create()
locationRequest.priority = LocationRequest.PRIORITY_LOW_POWER

val locationCallback = object : LocationCallback() {
      override fun onLocationResult(locationResult: LocationResult?) {
           if (locationResult == null) {
               return
            }
            for (location in locationResult.locations) {
                if (location != null) {
                    val latitude = location.latitude
                    val longitude = location.longitude
                    try {
                        val geocoder = Geocoder(activity, Locale.getDefault())
                        val addresses: List<Address> = geocoder.getFromLocation(latitude, longitude, maxResults)
                        for (address: Address in addresses) {
                            if (address.adminArea != null) {
                                mutableLocation.value = address.adminArea
                            }
                        }
                    } catch (exception: IOException) {
                        Timber.e(exception, "Error Fetching Location")
                    }
                }
             }
        }
    }

Now call location service inside configure method:

LocationServices
                .getFusedLocationProviderClient(activity)
                .requestLocationUpdates(locationRequest, locationCallback, null)

Now observe data for current location inside the fragment from the view model. Save the current user location and go to the main activity:

private val geoLocationViewModel by viewModel<GeoLocationViewModel>()
geoLocationViewModel.location.observe(this, Observer { location ->
                searchLocationViewModel.saveSearch(location)
                redirectToMain()
            })

GIF

In a Nutshell

So, essentially the Eventyay Attendee should have this feature to show all the events nearby me or in my city, although the app was already doing the job, but we had to manually select the city or locality we wish to search, now after the addition of dedicated current location option, the app will be more user friendly and automated.

Resources

1. Google location services API: https://www.toptal.com/android/android-developers-guide-to-google-location-services-api
2. MVVM architecture in Android: https://proandroiddev.com/mvvm-architecture-viewmodel-and-livedata-part-1-604f50cda1

Tags

Eventyay, open-event, PlayServices, Location, MVVM, Fossasia, GSoC, Android, Kotlin