Capstone II — Location, Weather API, Google Maps, Geofencing

Key concepts

• FusedLocationProviderClient
• Runtime location permissions
• REST call with Retrofit + coroutines
• SupportMapFragment & Marker
• GeofencingClient + GeofenceBroadcastReceiver

Lectures in this day

1. 01

   Weather Section Overview

   Add a weather widget to the tour: 1) get the phone's location, 2) call OpenWeatherMap (a free weather API), 3) show temperature, humidity, and an icon. Use Retrofit (a networking library) with coroutines.

   Real life · Peeking out the window before packing for a trip — 'do I bring an umbrella?' — right inside the app.

   Practice · 3 quick questions

   1. Q1.Weather section adds…

      A.Location + weather API + UIB.New auth flowC.New database

   2. Q2.Weather data comes from…

      A.A weather HTTP APIB.Firestore onlyC.Room

   3. Q3.Networking library commonly used?

      A.Retrofit / OkHttp / KtorB.SQLiteC.Glide only

   Check answersPick one answer per question.
2. 02

   Detect Current Location (I)

   Add `ACCESS_FINE_LOCATION` to the manifest and ask the user for it at runtime with the Activity Result API. `FusedLocationProviderClient.lastLocation` gives a cached location fast — often good enough.

   Real life · Asking a passerby 'roughly where are we?' — quick answer, maybe off by a block, but plenty for a weather lookup.
   kotlin

   Copy

   val ask = registerForActivityResult(
       ActivityResultContracts.RequestPermission()
   ) { granted ->
       if (granted) fetchLocation()          0
   }
   
   ask.launch(Manifest.permission.ACCESS_FINE_LOCATION)

   Practice · 3 quick questions

   1. Q1.Location on Android uses…

      A.FusedLocationProviderClientB.GPS class onlyC.WebView

   2. Q2.Which permission is required?

      A.ACCESS_FINE_LOCATION or COARSEB.CAMERAC.INTERNET only

   3. Q3.You must request permission at…

      A.Runtime (API 23+)B.Compile timeC.Never

   Check answersPick one answer per question.
3. 03

   Detect Current Location (II)

   For a fresh (up-to-date) location, use `getCurrentLocation(PRIORITY_BALANCED_POWER_ACCURACY, null)`. It's a little slower but more accurate. Handle the case where location is off (null result).

   Real life · Asking a GPS instead of a passerby — takes a second longer, but pinpoints where you are.
   kotlin

   Copy

   @SuppressLint("MissingPermission")
   fun fetchLocation(onLoc: (Location) -> Unit) {
       LocationServices.getFusedLocationProviderClient(this)
           .getCurrentLocation(Priority.PRIORITY_BALANCED_POWER_ACCURACY, null)
           .addOnSuccessListener { loc -> loc?.let(onLoc) }
   }

   Practice · 3 quick questions

   1. Q1.If user denies location, you should…

      A.Explain why and offer settingsB.CrashC.Retry silently

   2. Q2.Background location needs…

      A.Extra ACCESS_BACKGROUND_LOCATION on newer APIsB.NothingC.Only fine location

   3. Q3.Cache last known location because…

      A.It's fast and often good enoughB.GPS is always instantC.You must

   Check answersPick one answer per question.
4. 04

   Get Weather Data

   Retrofit turns an interface into an HTTP client. Mark your API functions `suspend` so you can call them from a coroutine. Moshi or Gson converts the JSON reply into your data classes automatically.

   Real life · Calling a hotline that reads out today's forecast — you dial, they answer, you jot down what they say.
   kotlin

   Copy

   interface WeatherApi {
       @GET("data/2.5/weather")
       suspend fun current(
           @Query("lat") lat: Double,
           @Query("lon") lon: Double,
           @Query("appid") key: String,
           @Query("units") units: String = "metric",
       ): WeatherResponse
   }

   Practice · 3 quick questions

   1. Q1.Retrofit maps HTTP to…

      A.Kotlin interfaces with annotationsB.XML formsC.Bash scripts

   2. Q2.JSON parsing typically uses…

      A.Moshi / kotlinx.serialization / GsonB.Regex onlyC.XML parser

   3. Q3.Weather call needs…

      A.Lat/lon + API keyB.Only your nameC.Nothing

   Check answersPick one answer per question.
5. 05

   Weather Layout (I)

   Design the weather card: city name at the top, a huge temperature in the middle, a description under it, and an icon. Icon URL pattern is `https://openweathermap.org/img/wn/{icon}@2x.png`.

   Real life · The hero panel of the weather app you already use — one glance tells you if you need a jacket.
   xml

   Copy

   <class="tok-key">androidx.cardview.widget.CardView
       android:layout_width="match_parent" android:layout_height="wrap_content"
       android:layout_margin="16dp" app:cardCornerRadius="16dp">
       <class="tok-key">LinearLayout android:orientation="vertical" android:padding="20dp"
           android:layout_width="match_parent" android:layout_height="wrap_content">
           <class="tok-key">TextView android:id="@+id/city" android:textSize="22sp"
                     android:layout_width="wrap_content" android:layout_height="wrap_content" />
           <class="tok-key">TextView android:id="@+id/temp" android:textSize="48sp"
                     android:layout_width="wrap_content" android:layout_height="wrap_content" />
           <class="tok-key">ImageView android:id="@+id/icon"
                      android:layout_width="80dp" android:layout_height="80dp" />
       </class="tok-key">LinearLayout>
   </class="tok-key">androidx.cardview.widget.CardView>

   Practice · 3 quick questions

   1. Q1.Weather layout usually shows…

      A.Temp, conditions, icon, locationB.A video adC.Long form text

   2. Q2.Weather icon can be loaded with…

      A.Glide/Coil from URLB.manifest referenceC.Nothing

   3. Q3.Container of choice for a simple weather card?

      A.ConstraintLayoutB.TableLayoutC.AbsoluteLayout

   Check answersPick one answer per question.
6. 06

   Weather Layout (II)

   Add a row of small stat chips under the main card: humidity, wind, feels-like. Use a horizontal LinearLayout with equal weights so each chip takes the same width.

   Real life · The little widgets under the big temperature — humidity, wind, UV — the details you check second.

   Practice · 3 quick questions

   1. Q1.Show loading with…

      A.ProgressBar or shimmerB.Blank screenC.System reboot

   2. Q2.On network error show…

      A.A retry actionB.Silent failC.Force logout

   3. Q3.Refresh gesture uses…

      A.SwipeRefreshLayoutB.Long click onlyC.Nothing

   Check answersPick one answer per question.
7. 07

   Temperature Conversion

   OpenWeatherMap gives Celsius when you pass `units=metric`. To show Fahrenheit, use `f = c * 9/5 + 32`. Let the user pick their unit in settings, then remember it.

   Real life · Reading a Fahrenheit recipe when your oven is Celsius — one formula and you're cooking, not guessing.
   kotlin

   Copy

   fun cToF(c: Double) = c * 9 / 5 + 32
   
   val display = if (useFahrenheit)
       "${cToF(temp).toInt()}°F"
   else
       "${temp.toInt()}°C"

   Practice · 3 quick questions

   1. Q1.Celsius → Fahrenheit formula is…

      A.C * 9/5 + 32B.C + 32C.C * 2

   2. Q2.Kelvin → Celsius is…

      A.K - 273.15B.K + 273.15C.K * 2

   3. Q3.Store unit preference in…

      A.SharedPreferences / DataStoreB.ManifestC.colors.xml

   Check answersPick one answer per question.
8. 08

   Google Maps and Maps Fragment Overview

   Add the Maps SDK to Gradle. Drop a `SupportMapFragment` in your XML. In Kotlin call `getMapAsync` — you get a `GoogleMap` object. Add a Marker at the user's lat/lon and move the camera to that point.

   Real life · Pinning your current spot on a paper map so you can plan the walk to the museum.
   xml

   Copy

   <class="tok-key">fragment
       android:id="@+id/map"
       android:name="com.google.android.gms.maps.SupportMapFragment"
       android:layout_width="match_parent"
       android:layout_height="300dp" />
   
   <!-- In Kotlin: -->
   <!--
   (childFragmentManager.findFragmentById(R.id.map) as SupportMapFragment)
       .getMapAsync { map ->
           val here = LatLng(loc.latitude, loc.longitude)
           map.addMarker(MarkerOptions().position(here).title("You"))
           map.moveCamera(CameraUpdateFactory.newLatLngZoom(here, 14f))
       }
   -->

   Practice · 3 quick questions

   1. Q1.Google Maps in Android uses…

      A.MapFragment / SupportMapFragmentB.WebView onlyC.Canvas

   2. Q2.You need a…

      A.Maps API keyB.NothingC.Custom compiler

   3. Q3.Map is ready via callback…

      A.OnMapReadyCallbackB.onCreate onlyC.onStart

   Check answersPick one answer per question.
9. 09

   Geofencing Overview (I)

   A geofence is an invisible circle on the map. The OS watches it in the background and wakes your app when the user ENTERS, EXITS, or STAYS INSIDE. You don't need to keep checking — Android does it for you.

   Real life · A dog collar that beeps when the dog leaves the yard. You don't watch — the collar does.

   Practice · 3 quick questions

   1. Q1.Geofencing triggers when…

      A.Device enters/exits/dwells in a circular areaB.The app is uninstalledC.The screen rotates

   2. Q2.Each geofence has a…

      A.Center + radius + expirationB.FilenameC.Icon only

   3. Q3.Delivered via…

      A.A PendingIntent to a receiver/serviceB.A ToastC.The main thread only

   Check answersPick one answer per question.
10. 10

    Geofencing Overview (II)

    Register geofences with `GeofencingClient.addGeofences(...)` and a `PendingIntent` that fires a BroadcastReceiver when a boundary is crossed. On Android 10+ you also need background location permission (a separate ask).

    Real life · Handing a security company a list of 'alert zones' — they call you if anyone crosses one.
    kotlin

    Copy

    val fence = Geofence.Builder()
        .setRequestId("hotel")                                 0
        .setCircularRegion(lat, lon, 150f)                     1
        .setExpirationDuration(Geofence.NEVER_EXPIRE)
        .setTransitionTypes(
            Geofence.GEOFENCE_TRANSITION_ENTER or
            Geofence.GEOFENCE_TRANSITION_EXIT
        )
        .build()

    Practice · 3 quick questions

    1. Q1.Which permission is needed for geofences on newer APIs?

       A.ACCESS_BACKGROUND_LOCATIONB.CAMERAC.RECORD_AUDIO

    2. Q2.Register geofences with…

       A.GeofencingClient.addGeofencesB.startService onlyC.Firestore

    3. Q3.Remove them with…

       A.removeGeofencesB.System.exitC.startActivity

    Check answersPick one answer per question.
11. 11

    Location Detection Refactoring

    You'll need location in more than one screen. Move the code into a small `LocationHelper` class — every screen uses the same helper, and permission code isn't duplicated.

    Real life · Making one master keychain the whole family shares, instead of everyone copying their own set.
    kotlin

    Copy

    class LocationHelper(private val ctx: Context) {
        private val client = LocationServices.getFusedLocationProviderClient(ctx)
    
        @SuppressLint("MissingPermission")
        suspend fun current(): Location? = suspendCancellableCoroutine { cont ->
            client.getCurrentLocation(Priority.PRIORITY_BALANCED_POWER_ACCURACY, null)
                .addOnSuccessListener { cont.resume(it) {} }
                .addOnFailureListener { cont.resume(null) {} }
        }
    }

    Practice · 3 quick questions

    1. Q1.Refactor moves location logic into…

       A.A reusable class or repositoryB.Every ActivityC.Manifest

    2. Q2.It helps because…

       A.Testable + reusable + cleanerB.Faster CPUC.Bigger APK

    3. Q3.The Activity/Fragment now just…

       A.Observes resultsB.Handles GPS math itselfC.Ignores location

    Check answersPick one answer per question.
12. 12

    Create and Add Geofence (I)

    Build the Geofence object, wrap it in a `GeofencingRequest` (say what to trigger on initial state), then register it with a `PendingIntent` that names the BroadcastReceiver Android should call.

    Real life · Programming a smart lock: define the zone, wire up the door alarm, arm it.
    kotlin

    Copy

    val req = GeofencingRequest.Builder()
        .setInitialTrigger(GeofencingRequest.INITIAL_TRIGGER_ENTER)
        .addGeofence(fence)
        .build()
    
    val pi = PendingIntent.getBroadcast(
        ctx, 0,
        Intent(ctx, GeofenceReceiver::class.java),
        PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_MUTABLE,
    )
    
    geofencingClient.addGeofences(req, pi)

    Practice · 3 quick questions

    1. Q1.To make a geofence you supply…

       A.ID, lat, lon, radius, transitionsB.Only IDC.Only lat

    2. Q2.Transitions include…

       A.Enter, Exit, DwellB.Rotate, Zoom, PanC.Login, Logout

    3. Q3.Expiration NEVER_EXPIRE means…

       A.Stays until you remove itB.One-shotC.Never fires

    Check answersPick one answer per question.
13. 13

    Create and Add Geofence (II)

    When the tour ends, remove geofences with `removeGeofences(...)` so they don't keep waking your app. Also handle error codes — for example `GEOFENCE_NOT_AVAILABLE` if the user has turned off location.

    Real life · Disarming and packing up the alarm when you check out of the hotel.

    Practice · 3 quick questions

    1. Q1.Result of addGeofences is a…

       A.Task<Void> with success/failureB.Sync booleanC.Nothing

    2. Q2.Common failure cause?

       A.Missing background location permissionB.Wrong colorC.Old Kotlin

    3. Q3.Test on…

       A.A real device with location onB.Emulator without locationC.No device

    Check answersPick one answer per question.
14. 14

    Get Geofence Alert

    A BroadcastReceiver decodes the event and posts a notification like 'Arrived at hotel'. Keep the receiver's code SHORT — hand any heavy work off to WorkManager, because a receiver has only a few seconds to run.

    Real life · The alarm rings briefly, then hands off to the security team. Short ring, longer response.
    kotlin

    Copy

    class GeofenceReceiver : BroadcastReceiver() {
        override fun onReceive(ctx: Context, intent: Intent) {
            val ev = GeofencingEvent.fromIntent(intent) ?: return
            if (ev.hasError()) return
    
            val kind = when (ev.geofenceTransition) {
                Geofence.GEOFENCE_TRANSITION_ENTER -> "Arrived at"
                Geofence.GEOFENCE_TRANSITION_EXIT  -> "Left"
                else                                -> "Near"
            }
            val id = ev.triggeringGeofences?.firstOrNull()?.requestId ?: "zone"
            notify(ctx, "$kind $id")
        }
    }

    Practice · 3 quick questions

    1. Q1.Show an alert on geofence event using…

       A.A local notificationB.Only LogcatC.Toast that survives death

    2. Q2.Handle event in…

       A.A BroadcastReceiver or JobIntentService via PendingIntentB.Main thread onlyC.XML

    3. Q3.Extract event data with…

       A.GeofencingEvent.fromIntent(intent)B.intent.getStringC.manifest

    Check answersPick one answer per question.
15. 15

    Module 6 Summary

    You built a real cloud-connected app: sign-in, live data in Firestore, photos in Storage, weather over the internet, Google Maps, and geofencing. That's the same shape as apps in the Play Store.

    Real life · Graduation day. The app you built could ship tomorrow. From here it's about polishing your craft.

    Practice · 3 quick questions

    1. Q1.By Module 6's end you can build…

       A.A full Firebase app with location, maps, storage, geofencingB.Only a UI mockupC.Only offline apps

    2. Q2.Which is a good next step?

       A.Publish, add tests, or explore ComposeB.Uninstall Android StudioC.Forget everything

    3. Q3.Most important habit going forward?

       A.Build small projects regularlyB.Only read booksC.Only watch videos

    Check answersPick one answer per question.

Real-life analogies

Code examples

val client = LocationServices.getFusedLocationProviderClient(this)

@SuppressLint("MissingPermission")
fun fetchLocation(onResult: (Location) -> Unit) {
    client.lastLocation.addOnSuccessListener { loc ->
        loc?.let(onResult)
    }
}

interface WeatherApi {
    @GET("data/2.5/weather")
    suspend fun current(
        @Query("lat") lat: Double,
        @Query("lon") lon: Double,
        @Query("appid") key: String,
        @Query("units") units: String = "metric"
    ): WeatherResponse
}

class WeatherRepo(private val api: WeatherApi) {
    suspend fun near(lat: Double, lon: Double) =
        api.current(lat, lon, BuildConfig.OWM_KEY)
}

val geofence = Geofence.Builder()
    .setRequestId("home_zone")
    .setCircularRegion(23.8103, 90.4125, 200f) 0
    .setExpirationDuration(Geofence.NEVER_EXPIRE)
    .setTransitionTypes(Geofence.GEOFENCE_TRANSITION_ENTER)
    .build()

val request = GeofencingRequest.Builder()
    .setInitialTrigger(GeofencingRequest.INITIAL_TRIGGER_ENTER)
    .addGeofence(geofence).build()

geofencingClient.addGeofences(request, geofencePendingIntent)

Hands-on checklist

• Add ACCESS_FINE_LOCATION runtime permission flow
• Detect current location & pass lat/lon to weather API
• Embed Google Map + drop a marker at current location
• Add a geofence and log/notify on ENTER

Milestone

Common pitfalls

• Skipping ACCESS_BACKGROUND_LOCATION on Android 10+ — geofences won't fire reliably.
• Hard-coding your API key in code — use local.properties + BuildConfig.