C#

public class GcmSender
    {
        private const string GcmUri = "https://android.googleapis.com/gcm/send";

        #region Properties

        public string DeviceToken { get; set; }
        public string ApiKey { get; set; }
        public string ResultJson { get; private set; }

        #endregion

        HttpWebRequest _gcmRequest;
        HttpWebResponse _gcmResponse;

        public GcmSender()
        {
            // do nothing
        }

        public GcmSender(string deviceToken, string apiKey)
        {
            DeviceToken = deviceToken;
            ApiKey = apiKey;
        }

        public string Send(string message)
        {
            // Escape condition
            if (DeviceToken == null || ApiKey == null)
            {
                return "[ERROR] Device Token or API Key has not been set";
            }

            InitGcmClient();
            PostPayload(message);

            try
            {
                _gcmResponse = _gcmRequest.GetResponse() as HttpWebResponse;
            }
            catch (WebException we)
            {
                return "[ERROR] There is a problem within processing GCM message \n" + we.Message;
            }
            ResultJson = ReadResponse(_gcmResponse);

            return ResultJson;
        }

        private string ReadResponse(HttpWebResponse response)
        {
            StreamReader responseReader = new StreamReader(response.GetResponseStream());
            return responseReader.ReadToEnd();
        }

        private void InitGcmClient()
        {
            _gcmRequest = WebRequest.Create(GcmUri) as HttpWebRequest;
            if (_gcmRequest != null)
            {
                _gcmRequest.ContentType = "application/json";
                _gcmRequest.UserAgent = "Android GCM Message Sender Client 1.0";
                _gcmRequest.Method = "POST";

                // Credential info
                _gcmRequest.Headers.Add("Authorization", "key=" + ApiKey);
            }
        }

        private void PostPayload(string message)
        {
            // Ready
            string payloadString = AssembleJSONPayload(DeviceToken, message);
            byte[] payloadByte = Encoding.UTF8.GetBytes(payloadString);
            _gcmRequest.ContentLength = payloadByte.Length;

            // Go
            using (Stream payloadStream = _gcmRequest.GetRequestStream())
            {
                payloadStream.Write(payloadByte, 0, payloadByte.Length);
                payloadStream.Close();
            }
        }

        private string AssembleJSONPayload(string gcmDeviceToken, string gcmBody)
        {
            string payloadFormatJSON =
                "{{" +
                    "\"registration_ids\" : [\"{0}\"]," +
                    "\"data\" : {{" +
                        " {1} " +
                    "}}" +
                "}}";

            string payload = string.Format(payloadFormatJSON, gcmDeviceToken, gcmBody);
            Debug.WriteLine("payload : " + payload);

            return payload;
        }
    }

_gcmResponse = _gcmRequest.GetResponse() as HttpWebResponse;

The remote server returned an error: (400) Bad Request.

// Updates to the App class
public partial class App : Application
{
  private bool _active;

  public bool Active { get { return _active; } }
  private void Application_Activated(object sender, EventArgs e)
  {
    _active = true;
  }
  private void Application_Deactivated(object sender, EventArgs e)
  {
    _active = false;
  }
}

// Popup event handler
public void PopupBase_MouseDown(object sender, EventArgs e)
{
  App currentApp = Application.Current as App;
  if (currentApp != null)
  {
    if (!currentApp.Active)
    {
      _owner.Activate();
    }
  }
}

// This was set to trigger on the Popup.Child's Loaded event
public void PopupChild_Loaded(object sender, EventArgs e)
{
  AddActivationHandler(this.Child.Child);  // Child is Border and the border's child is a Grid
}
private void AddActivationHandler(UIElement element)
{
  if (element is Panel)
  {
    Panel pElement = element as Panel;
    foreach (UIElement child in pElement.Children) // Recursively iterate through all children and children of children
    {
      AddActivationHandler(child);
    }
  }

  element.MouseDown += PopupBase_MouseDown;
{

double totalDistance = 7.3
double speed = 1;
double progress = (speed / totalDistance);
double step = progress / 10;

    while (progress <= totalDistance)
    {
        progress += step;

        //Calling a function that updates between 0.0 and 1
        Dispatcher.Invoke(new Action(() => {
            SetProgress(0.1);
        }));
    }