Chitranshi Srivastava Android

Fetching & Saving User's Current Location 👤📍

Fetching & Saving User's Current Location 👤📍

Chitranshi Srivastava's photo
Chitranshi Srivastava
·

4 min read

This stunt is divided into 3 parts -

  1. Preparing to get the user's device location (getting the permissions, setting up the UI, etc.)
  2. Getting the user's current device location
  3. Saving the map state & camera position

Okay so shut all the distractions, get hydrated, we'll now get these parts done. lets-go-dwight-schrute.gif

  1. Prepare to get the user's device location

    1. Enable the Places SDK in the Google Cloud project you just created.
      • Google Cloud console -> select your project -> APIs -> Places SDK -> Enable
    2. Add Places dependency (app: build.gradle)

    3. Instantiate the Places API client

      • Create a PlacesClient object & a FusedLocationProviderClient object.

          // MapsActivity.kt

  private lateinit var placesClient: PlacesClient
  private lateinit var fusedLocationProviderClient: FusedLocationProviderClient

  override fun onCreate(savedInstanceState: Bundle?) {
          ...

          // Create PlacesClient
      Places.initialize(applicationContext, getString(R.string.maps_api_key))
      placesClient = Places.createClient(this)

      // Create FusedLocationProviderClient
      fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this)
  }

    4. Request location permission

      • Add fine location permission in your app for FINE_LOCATION

          // AndroidManifest.xml

  <!--
       The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
       Google Maps Android API v2, but you must specify either coarse or fine
       location permissions for the "MyLocation" functionality.
  -->
  <uses-permissionandroid:name="android.permission.ACCESS_FINE_LOCATION" />

      • Request run-time permission for FINE_LOCATION

              // MapsActivity.kt

          private var locationPermissionGranted = false

          private fun getLocationPermission() {
          /*
           * Request location permission, so that we can get the location of the
           * device. The result of the permission request is handled by a callback,
           * onRequestPermissionsResult.
           */
          if (ContextCompat.checkSelfPermission(this.applicationContext, 
                  android.Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
              locationPermissionGranted = true
          } else {
              ActivityCompat.requestPermissions(this, 
                  arrayOf(android.Manifest.permission.ACCESS_FINE_LOCATION), 
                  PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION
              )
          }
      }

          companion object {
              private const val PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION = 111
          }

      • Handle the result of the request permission

                  // MapsActivity.kt        

          override fun onRequestPermissionsResult(requestCode: Int,
                                              permissions: Array<String>,
                                              grantResults: IntArray) {
          super.onRequestPermissionsResult(requestCode, permissions, grantResults)
          locationPermissionGranted = false
          when (requestCode) {
              PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION -> {

                  // If request is cancelled, the result arrays are empty. But if the user has now
                  // granted the permission (after we requested), the result array contains that permission.
                  if (grantResults.isNotEmpty() &&
                      grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                      locationPermissionGranted = true
                  }
              }
          }
      }

    5. Update the UI

      • Update the UI if the user has granted permission

          // mAPSaCTIVITY.KT
  private var lastKnownLocation = null

  override fun onMapReady(googleMap: GoogleMap) {
      ...
      // Turn on the My Location layer and the related control on the map.
      updateLocationUI()
  }

  override fun onRequestPermissionsResult(...) {
      ...
      updateLocationUI()
  }        

  private fun updateLocationUI() {
      /**
       * If the user has granted the FINE_LOCATION permission, update the UI else don't
       */
      if (mMap == null) {
          return
      }
      try {
          if (locationPermissionGranted) {
              mMap.isMyLocationEnabled = true
              mMap.uiSettings.isMyLocationButtonEnabled = true
          } else {
              mMap.isMyLocationEnabled = false
              mMap.uiSettings.isMyLocationButtonEnabled = false
              lastKnownLocation = null
              getLocationPermission()
          }
      } catch (e: SecurityException) {
          Log.e("Exception: %s", e.message, e)
      }
  }

  2. Get the location of the Android device and position the map

    • get the device location

            // MapsActivity.kt

          private var lastKnownLocation: Location? = null
          private val defaultLocation = LatLng(-34.0, 151.0)      // Sydney        

          override fun onMapReady(googleMap: GoogleMap) {
                  ...
              // Get the current location of the device and set the position of the map.
              getDeviceLocation()
          }

          private fun getDeviceLocation() {
          /*
           * Get the best and most recent location of the device, which may be null in rare
           * cases when a location is not available.
           */
          try {
              if (locationPermissionGranted) {
                  val locationResult = fusedLocationProviderClient.lastLocation
                  locationResult.addOnCompleteListener(this) { task ->
                      if (task.isSuccessful) {
                          // Set the map's camera position to the current location of the device.
                          lastKnownLocation = task.result
                          if (lastKnownLocation != null) {
                              mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(
                                  LatLng(lastKnownLocation!!.latitude,
                                      lastKnownLocation!!.longitude), DEFAULT_ZOOM))
                          }
                      } else {
                          Log.d(TAG, "Current location is null. Using defaults.")
                          Log.e(TAG, "Exception: %s", task.exception)
                          mMap.moveCamera(CameraUpdateFactory
                              .newLatLngZoom(defaultLocation, DEFAULT_ZOOM))
                          mMap.uiSettings.isMyLocationButtonEnabled = false
                      }
                  }
              }
          } catch (e: SecurityException) {
              Log.e("Exception: %s", e.message, e)
          }
      }

      companion object {
           private const val DEFAULT_ZOOM = 50F
       }

      Now run the app. After allowing the app to get your location, you'll see that the map zooms in to your current location, displaying a blue circle at your precise latitude & longitude. Great! 🍻 55.png 44.png

  3. Save the map's state

    • Save map's state & camera position

      • Set up the values that you want to save
      • Save the state

      • Retrieve the saved state on onCreate()

        // MapsActivity.kt        

private var cameraPosition: CameraPosition? = CameraPosition(defaultLocation, DEFAULT_ZOOM, 0.0F, 0.0F)

  override fun onCreate(savedInstanceState: Bundle?) {
      ...
      // Retrieve the user's saved map state & camera position
      if (savedInstanceState != null) {
          lastKnownLocation = savedInstanceState.getParcelable(KEY_LOCATION)
          cameraPosition = savedInstanceState.getParcelable(KEY_CAMERA_POSITION)
      }
  }

  override fun onSaveInstanceState(outState: Bundle) {
      /**
       * Save the map's state & camera position when the activity is destroyed
       * (like in a configuration change)
       */
      mMap.let { map ->
          outState.putParcelable(KEY_CAMERA_POSITION, map.cameraPosition)
          outState.putParcelable(KEY_LOCATION, lastKnownLocation)
      }
      super.onSaveInstanceState(outState)
  }

  companion object {
      ...
      private const val KEY_CAMERA_POSITION = "camera_position"
      private const val KEY_LOCATION = "location"
  }

This is it. Now run the app & rotate it. You'll see the marker persists. You've now successfully fetched & saved your app's user's current location! 🎊

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