using CardDav;
using CardDav.Card;
using CardDav.Response;

CardDav.Client client = new CardDav.Client("url of carddav server go here", "username", "some password");

CardDavResponse response = client.Get();

/** Output the results from the Listing **/

//Assuming you have a result text box to output too :P

resultsTxt.Text = response.ToString();

/** Set the client to the proper Address Book server URL **/
// This is heavily assumming that there are address books and vcards!
// Always check to see if CardDavResponse.AddressBooks.Count > 0
// And always check to see if CardDavResponse.Cards.Count > 0

client.SetServer(response.AddressBooks.First().Url.ToString());
vCard card = client.GetVCard(response.Cards.First().Id);

//Assuming you have a result text box to output too :P

resultsTxt.Text = resultsTxt.Text + "\r\n\r\n\r\n" + card.ToString();

CardDav.Client client = new CardDav.Client("url of carddav server go here", "your OAuth 2.0 access token");