private async void RemoveHeaders(ListView selectedItems)
 {
     for (int index = selectedItems.SelectedItems.Count - 1; index >= 0; index--)
     {
         RTHeaders header = selectedItems.SelectedItems[index] as RTHeaders;
         Headers.Remove(header);
     }
 }
 private void AddHeader()
 {
     try
     {
         RTHeaders header = new RTHeaders()
         {
             Key = HeaderKey, Value = HeaderValue
         };
         Headers.Add(header);
         HeaderKey   = "";
         HeaderValue = "";
         RaisePropertyChanged();
     }
     catch (Exception)
     {
     }
 }