IP address in WPF

Hi friends,
I try to get the ip of the local computer in WPF but it fail...
I allready done that in WinForm but in WPF it does not work.
can someone give me a little code that works?
Thank you all.

Post the code that you are using to grab the IP in WinForms.

IPAddress[] a = Dns.GetHostByName(Dns.GetHostName()).AddressList;


string ip = a[0].ToString();
txtIp.Text = ip;

What exactly doesn't work?