[Huawei Developers] tugcearar:
A geofence is a virtual perimeter set on a real geographic area. Combining a user position with a geofence perimeter, it is possible to know if the user is inside the geofence or if he is exiting or entering the area.

In this article, we will discuss how to use the geofence to notify the user when the device enters/exits an area using the HMS Location Kit in a Xamarin.Android application. We will also add and customize HuaweiMap, which includes drawing circles, adding pointers, and using nearby searches in search places. We are going to learn how to use the below features together:

Geofence

Reverse Geocode

HuaweiMap

Nearby Search

First of all, you need to be a registered Huawei Mobile Developer and create an application in Huawei App Console in order to use HMS Map Location and Site Kits. You can follow there steps in to complete the configuration that required for development.

Configuring App Information in AppGallery Connect --> shorturl.at/rL347

Creating Xamarin Android Binding Libraries --> shorturl.at/rBP46

Integrating the HMS Map Kit Libraries for Xamarin --> shorturl.at/vAHPX

Integrating the HMS Location Kit Libraries for Xamarin --> shorturl.at/dCX07

Integrating the HMS Site Kit Libraries for Xamarin --> shorturl.at/bmDX6

Integrating the HMS Core SDK --> shorturl.at/qBISV

Setting Package in Xamarin --> shorturl.at/brCU1

When we create our Xamarin.Android application in the above steps, we need to make sure that the package name is the same as we entered the Console. Also, don’t forget the enable them in Console.

Manifest & Permissions

We have to update the application’s manifest file by declaring permissions that we need as shown below.

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />

Also, add a meta-data element to embed your app id in the application tag, it is required for this app to authenticate on the Huawei’s cloud server. You can find this id in agconnect-services.json file.

<meta-data android:name="com.huawei.hms.client.appid" android:value="appid=YOUR_APP_ID" />

Request location permission

private void RequestPermissions()
{
if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.AccessCoarseLocation) != (int)Permission.Granted ||
ContextCompat.CheckSelfPermission(this, Manifest.Permission.AccessFineLocation) != (int)Permission.Granted ||
ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != (int)Permission.Granted ||
ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadExternalStorage) != (int)Permission.Granted ||
ContextCompat.CheckSelfPermission(this, Manifest.Permission.Internet) != (int)Permission.Granted)
{
ActivityCompat.RequestPermissions(this,
new System.String[]
{
Manifest.Permission.AccessCoarseLocation,
Manifest.Permission.AccessFineLocation,
Manifest.Permission.WriteExternalStorage,
Manifest.Permission.ReadExternalStorage,
Manifest.Permission.Internet
},
100);
}
else
GetCurrentPosition();

}

Add a Map

Add a <fragment> element to your activity’s layout file, activity_main.xml. This element defines a MapFragment to act as a container for the map and to provide access to the HuaweiMap object.

<fragment
android:id="@+id/mapfragment"
class="com.huawei.hms.maps.MapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"/>

Implement the IOnMapReadyCallback interface to MainActivity and override OnMapReady method which is triggered when the map is ready to use. Then use GetMapAsync to register for the map callback.

We request the address corresponding to a given latitude/longitude. Also specified that the output must be in JSON format.

public class MainActivity : AppCompatActivity, IOnMapReadyCallback
{
...
public void OnMapReady(HuaweiMap map)
{
hMap = map;
hMap.UiSettings.MyLocationButtonEnabled = true;
hMap.UiSettings.CompassEnabled = true;
hMap.UiSettings.ZoomControlsEnabled = true;
hMap.UiSettings.ZoomGesturesEnabled = true;
hMap.MyLocationEnabled = true;
hMap.MapClick += HMap_MapClick;

if (selectedCoordinates == null)
selectedCoordinates = new GeofenceModel { LatLng = CurrentPosition, Radius = 30 };
}
}

As you can see above, with the UiSettings property of the HuaweiMap object we set my location button, enable compass, etc. Now when the app launch, directly get the current location and move the camera to it. In order to do that we use FusedLocationProviderClient that we instantiated and call LastLocation API.

LastLocation API returns a Task object that we can check the result by implementing the relevant listeners for success and failure.In success listener we are going to move the map’s camera position to the last known position.

private void GetCurrentPosition()
{
var locationTask = fusedLocationProviderClient.LastLocation;
locationTask.AddOnSuccessListener(new LastLocationSuccess(this));
locationTask.AddOnFailureListener(new LastLocationFail(this));
}
...
public class LastLocationSuccess : Java.Lang.Object, IOnSuccessListener
{
...
public void OnSuccess(Java.Lang.Object location)
{
Toast.MakeText(mainActivity, "LastLocation request successful", ToastLength.Long).Show();
if (location != null)
{
MainActivity.CurrentPosition = new LatLng((location as Location).Latitude, (location as Location).Longitude);
mainActivity.RepositionMapCamera((location as Location).Latitude, (location as Location).Longitude);
}
}

}

To change the position of the camera, we must specify where we want to move the camera, using a CameraUpdate. The Map Kit allows us to create many different types of CameraUpdate using CameraUpdateFactory.

There are some methods for the camera position changes as we see above. Simply these are:

NewLatLng: Change camera’s latitude and longitude, while keeping other properties

NewLatLngZoom: Changes the camera’s latitude, longitude, and zoom, while keeping other properties

NewCameraPosition: Full flexibility in changing the camera position

We are going to use NewCameraPosition. A CameraPosition can be obtained with a CameraPosition.Builder. And then we can set target, bearing, tilt and zoom properties.

public void RepositionMapCamera(double lat, double lng)
{
var cameraPosition = new CameraPosition.Builder();
cameraPosition.Target(new LatLng(lat, lng));
cameraPosition.Zoom(1000);
cameraPosition.Bearing(45);
cameraPosition.Tilt(20);
CameraUpdate cameraUpdate = CameraUpdateFactory.NewCameraPosition(cameraPosition.Build());
hMap.MoveCamera(cameraUpdate);
}

Creating Geofence

In this part, we will choose the location where we want to set geofence in two different ways. The first is to select the location by clicking on the map, and the second is to search for nearby places by keyword and select one after placing them on the map with the marker.

Set the geofence location by clicking on the map

It is always easier to select a location by seeing it. After this section, we are able to set a geofence around the clicked point when the map’s clicked. We attached the Click event to our map in the OnMapReady method. In this Click event, we will add a marker to the clicked point and draw a circle around it.

Also, we will use the Seekbar at the bottom of the page to adjust the circle radius. We set selectedCoordinates variable when adding the marker. Let’s create the following method to create the marker:

private void HMap_MapClick(object sender, HuaweiMap.MapClickEventArgs e)
{
selectedCoordinates.LatLng = e.P0;
if (circle != null)
{
circle.Remove();
circle = null;
}
AddMarkerOnMap();
}
void AddMarkerOnMap()
{
if (marker != null) marker.Remove();
var markerOption = new MarkerOptions()
.InvokeTitle("You are here now")
.InvokePosition(selectedCoordinates.LatLng);
hMap.SetInfoWindowAdapter(new MapInfoWindowAdapter(this));
marker = hMap.AddMarker(markerOption);
bool isInfoWindowShown = marker.IsInfoWindowShown;
if (isInfoWindowShown)
marker.HideInfoWindow();
else
marker.ShowInfoWindow();
}

Adding MapInfoWindowAdapter class to our project for rendering the custom info model. And implement HuaweiMap.IInfoWindowAdapter interface to it. When an information window needs to be displayed for a marker, methods provided by this adapter are called in any case.

Now let’s create a custom info window layout and named it as map_info_view.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:text="Add geofence"
android:width="100dp"
style="@style/Widget.AppCompat.Button.Colored"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/btnInfoWindow" />
</LinearLayout>

And return it after customizing it in GetInfoWindow() method. The full code of the adapter is below:

internal class MapInfoWindowAdapter : Java.Lang.Object, HuaweiMap.IInfoWindowAdapter
{
private MainActivity activity;
private GeofenceModel selectedCoordinates;
private View addressLayout;
public MapInfoWindowAdapter(MainActivity currentActivity){activity = currentActivity;}
public View GetInfoContents(Marker marker){return null;}
public View GetInfoWindow(Marker marker)
{
if (marker == null)
return null;
selectedCoordinates = new GeofenceModel { LatLng = new LatLng(marker.Position.Latitude, marker.Position.Longitude) };
View mapInfoView = activity.LayoutInflater.Inflate(Resource.Layout.map_info_view, null);
var radiusBar = activity.FindViewById<SeekBar>(Resource.Id.radiusBar);
if (radiusBar.Visibility == Android.Views.ViewStates.Invisible)
{
radiusBar.Visibility = Android.Views.ViewStates.Visible;
radiusBar.SetProgress(30, true);
}
activity.FindViewById<SeekBar>(Resource.Id.radiusBar)?.SetProgress(30, true);
activity.DrawCircleOnMap(selectedCoordinates);
Button button = mapInfoView.FindViewById<Button>(Resource.Id.btnInfoWindow);
button.Click += btnInfoWindow_ClickAsync;
return mapInfoView;
}
}

Now we create a method to arrange a circle around the marker that representing the geofence radius. Create a new DrawCircleOnMap method in MainActivity for this. To construct a circle, we must specify the Center and Radius. Also, I set other properties like StrokeColor etc.

public void DrawCircleOnMap(GeofenceModel geoModel)
{
if (circle != null)
{
circle.Remove();
circle = null;
}
CircleOptions circleOptions = new CircleOptions()
.InvokeCenter(geoModel.LatLng)
.InvokeRadius(geoModel.Radius)
.InvokeFillColor(Color.Argb(50, 0, 14, 84))
.InvokeStrokeColor(Color.Yellow)
.InvokeStrokeWidth(15);
circle = hMap.AddCircle(circleOptions);
}
private void radiusBar_ProgressChanged(object sender, SeekBar.ProgressChangedEventArgs e)
{
selectedCoordinates.Radius = e.Progress;
DrawCircleOnMap(selectedCoordinates);
}

We will use SeekBar to change the radius of the circle. As the value changes, the drawn circle will expand or shrink.

Reverse Geocoding

Now let’s handle the click event of the info window.

But before open that window, we need to reverse geocoding selected coordinates to getting a formatted address. HUAWEI Site Kit provides us a set of HTTP API including the one that we need, reverseGeocode.

Let’s add the GeocodeManager class to our project and update it as follows:

public async Task<Site> ReverseGeocode(double lat, double lng)
{
string result = "";
using (var client = new HttpClient())
{
MyLocation location = new MyLocation();
location.Lat = lat;
location.Lng = lng;
var root = new ReverseGeocodeRequest();
root.Location = location;

var settings = new JsonSerializerSettings();
settings.ContractResolver = new LowercaseSerializer();
var json = JsonConvert.SerializeObject(root, Formatting.Indented, settings);

var data = new StringContent(json, Encoding.UTF8, "application/json");
var url = "siteapi.cloud.huawei.com/mapApi/v1/siteService/reverseGeocode?key=" + Android.Net.Uri.Encode(ApiKey);
var response = await client.PostAsync(url, data);
result = response.Content.ReadAsStringAsync().Result;
}

return JsonConvert.DeserializeObject<ReverseGeocodeResponse>(result).sites.FirstOrDefault();
}

In the above code, we request the address corresponding to a given latitude/longitude. Also specified that the output must be in JSON format.

Request model:

public class MyLocation
{
public double Lat { get; set; }
public double Lng { get; set; }
}
public class ReverseGeocodeRequest
{
public MyLocation Location { get; set; }
}

Note that the JSON response contains three root elements:

“returnCode”: For details, please refer to Result Codes.

“returnDesc”: description

“sites” contains an array of geocoded address information

Generally, only one entry in the “sites” array is returned for address lookups, though the geocoder may return several results when address queries are ambiguous.

Add the following codes to our MapInfoWindowAdapter where we get results from the Reverse Geocode API and set the UI elements.

private async void btnInfoWindow_ClickAsync(object sender, System.EventArgs e)
{
addressLayout = activity.LayoutInflater.Inflate(Resource.Layout.reverse_alert_layout, null);
GeocodeManager geocodeManager = new GeocodeManager(activity);
var addressResult = await geocodeManager.ReverseGeocode(selectedCoordinates.LatLng.Latitude, selectedCoordinates.LatLng.Longitude);
if (addressResult.ReturnCode != 0)
return;
var address = addressResult.Sites.FirstOrDefault();
var txtAddress = addressLayout.FindViewById<TextView>(Resource.Id.txtAddress);
var txtRadius = addressLayout.FindViewById<TextView>(Resource.Id.txtRadius);
txtAddress.Text = address.FormatAddress;
txtRadius.Text = selectedCoordinates.Radius.ToString();
AlertDialog.Builder builder = new AlertDialog.Builder(activity);
builder.SetView(addressLayout);
builder.SetTitle(address.Name);
builder.SetPositiveButton("Save", (sender, arg) =>
{
selectedCoordinates.Conversion = GetSelectedConversion();
GeofenceManager geofenceManager = new GeofenceManager(activity);
geofenceManager.AddGeofences(selectedCoordinates);
});
builder.SetNegativeButton("Cancel", (sender, arg) => { builder.Dispose(); });
AlertDialog alert = builder.Create();
alert.Show();
}

Now, after selecting the conversion, we can complete the process by calling the AddGeofence method in the GeofenceManager class by pressing the save button in the dialog window.

public void AddGeofences(GeofenceModel geofenceModel)
{
//Set parameters
geofenceModel.Id = Guid.NewGuid().ToString();
if (geofenceModel.Conversion == 5) //Expiration value that indicates the geofence should never expire.
geofenceModel.Timeout = Geofence.GeofenceNeverExpire;
else
geofenceModel.Timeout = 10000;

List<IGeofence> geofenceList = new List<IGeofence>();

//Geofence Service
GeofenceService geofenceService = LocationServices.GetGeofenceService(activity);
PendingIntent pendingIntent = CreatePendingIntent();
GeofenceBuilder somewhereBuilder = new GeofenceBuilder()
.SetUniqueId(geofenceModel.Id)
.SetValidContinueTime(geofenceModel.Timeout)
.SetRoundArea(geofenceModel.LatLng.Latitude, geofenceModel.LatLng.Longitude, geofenceModel.Radius)
.SetDwellDelayTime(10000)
.SetConversions(geofenceModel.Conversion); ;

//Create geofence request
geofenceList.Add(somewhereBuilder.Build());
GeofenceRequest geofenceRequest = new GeofenceRequest.Builder()
.CreateGeofenceList(geofenceList)
.Build();

//Register geofence
var geoTask = geofenceService.CreateGeofenceList(geofenceRequest, pendingIntent);
geoTask.AddOnSuccessListener(new CreateGeoSuccessListener(activity));
geoTask.AddOnFailureListener(new CreateGeoFailListener(activity));
}

In the AddGeofence method, we need to set the geofence request parameters, like the selected conversion, unique Id and timeout according to conversion, etc. with GeofenceBuilder. We create GeofenceBroadcastReceiver and display a toast message when a geofence action occurs.

[BroadcastReceiver(Enabled = true)]
[IntentFilter(new[] { "com.huawei.hms.geofence.ACTION_PROCESS_ACTIVITY" })]
class GeofenceBroadcastReceiver : BroadcastReceiver
{
public static readonly string ActionGeofence = "com.huawei.hms.geofence.ACTION_PROCESS_ACTIVITY";
public override void OnReceive(Context context, Intent intent)
{
if (intent != null)
{
var action = intent.Action;
if (action == ActionGeofence)
{
GeofenceData geofenceData = GeofenceData.GetDataFromIntent(intent);
if (geofenceData != null)
{
Toast.MakeText(context, "Geofence triggered: " + geofenceData.ConvertingLocation.Latitude +"\n" + geofenceData.ConvertingLocation.Longitude + "\n" + geofenceData.Conversion.ToConversionName(), ToastLength.Long).Show();
}
}
}
}
}

After that in CreateGeoSuccessListener and CreateGeoFailureListener that we implement IOnSuccessListener and IOnFailureListener respectively, we display a toast message to the user like this:

public class CreateGeoFailListener : Java.Lang.Object, IOnFailureListener
{
public void OnFailure(Java.Lang.Exception ex)
{
Toast.MakeText(mainActivity, "Geofence request failed: " + GeofenceErrorCodes.GetErrorMessage((ex as ApiException).StatusCode), ToastLength.Long).Show();
}
}

public class CreateGeoSuccessListener : Java.Lang.Object, IOnSuccessListener
{
public void OnSuccess(Java.Lang.Object data)
{
Toast.MakeText(mainActivity, "Geofence request successful", ToastLength.Long).Show();
}
}

Set geofence location using Nearby Search

On the main layout when the user clicks the Search Nearby Places button, a search dialog like below appears:

Create search_alert_layout.xml with a search input In Main Activity, create click event of that button and open an alert dialog after it’s view is set to search_alert_layout. And make NearbySearch when clicking the Search button:

private void btnGeoWithAddress_Click(object sender, EventArgs e)
{
search_view = base.LayoutInflater.Inflate(Resource.Layout.search_alert_layout, null);
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.SetView(search_view);
builder.SetTitle("Search Location");
builder.SetNegativeButton("Cancel", (sender, arg) => { builder.Dispose(); });
search_view.FindViewById<Button>(Resource.Id.btnSearch).Click += btnSearchClicked;
alert = builder.Create();
alert.Show();
}
private void btnSearchClicked(object sender, EventArgs e)
{
string searchText = search_view.FindViewById<TextView>(Resource.Id.txtSearch).Text;
GeocodeManager geocodeManager = new GeocodeManager(this);
geocodeManager.NearbySearch(CurrentPosition, searchText);
}

We pass search text and Current Location into the GeocodeManager NearbySearch method as parameters. We need to modify GeoCodeManager class and add nearby search method to it.

public void NearbySearch(LatLng currentLocation, string searchText)
{
ISearchService searchService = SearchServiceFactory.Create(activity, Android.Net.Uri.Encode("YOUR_API_KEY"));
NearbySearchRequest nearbySearchRequest = new NearbySearchRequest();
nearbySearchRequest.Query = searchText;
nearbySearchRequest.Language = "en";
nearbySearchRequest.Location = new Coordinate(currentLocation.Latitude, currentLocation.Longitude);
nearbySearchRequest.Radius = (Integer)2000;
nearbySearchRequest.PageIndex = (Integer)1;
nearbySearchRequest.PageSize = (Integer)5;
nearbySearchRequest.PoiType = LocationType.Address;
searchService.NearbySearch(nearbySearchRequest, new QuerySuggestionResultListener(activity as MainActivity));
}

And to handle the result we must create a listener and implement the ISearchResultListener interface to it.

public class NearbySearchResultListener : Java.Lang.Object, ISearchResultListener
{
public void OnSearchError(SearchStatus status)
{
Toast.MakeText(context, "Error Code: " + status.ErrorCode + " Error Message: " + status.ErrorMessage, ToastLength.Long);
}
public void OnSearchResult(Java.Lang.Object results)
{
NearbySearchResponse nearbySearchResponse = (NearbySearchResponse)results;
if (nearbySearchResponse != null && nearbySearchResponse.TotalCount > 0)
context.SetSearchResultOnMap(nearbySearchResponse.Sites);
}
}

In OnSearchResult method, NearbySearchResponse object return. We will insert markers to the mapper element in this response. The map will look like this:

In Main Activity create a method named SetSearchResultOnMap and pass IList<Site> as a parameter to insert multiple markers on the map.

public void SetSearchResultOnMap(IList<Com.Huawei.Hms.Site.Api.Model.Site> sites)
{
hMap.Clear();
if (searchMarkers != null && searchMarkers.Count > 0)
foreach (var item in searchMarkers)
item.Remove();
searchMarkers = new List<Marker>();
for (int i = 0; i < sites.Count; i++)
{
MarkerOptions marker1Options = new MarkerOptions()
.InvokePosition(new LatLng(sites[i].Location.Lat, sites[i].Location.Lng))
.InvokeTitle(sites[i].Name).Clusterable(true);
hMap.SetInfoWindowAdapter(new MapInfoWindowAdapter(this));
var marker1 = hMap.AddMarker(marker1Options);
searchMarkers.Add(marker1);
RepositionMapCamera(sites[i].Location.Lat, sites[i].Location.Lng);
}
hMap.SetMarkersClustering(true);
alert.Dismiss();
}

Now, we add markers as we did above. But here we use SetMarkersClustering(true) to consolidates markers into clusters when zooming out of the map.

You can download the source code from below:

github.com/stugcearar/HMSCore-Xamarin-Android-Samples/tree/master/LocationKit/HMS_Geofence

Also if you have any questions, ask away in Huawei Developer Forums.

Errors

If your location permission set “Allowed only while in use instead” of ”Allowed all the time” below exception will be thrown.

int GEOFENCE_INSUFFICIENT_PERMISSION

Insufficient permission to perform geofence-related operations.

You can see all result codes including errors, in here for Location service.

You can find result codes with details here for Geofence request.