GeocodeManager.cs

class GeocodeManager
{
    public const string ApiKey = "YOUR_API_KEY”
    private MainActivity activity;
    public GeocodeManager(MainActivity activity)
    {
        this.activity = activity;
    }

    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 = "https://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();
    }
}