public void ConstructDnsPermission() {
  try 
  {
    // Create a DnsPermission instance.
    DnsPermission permission = new DnsPermission(PermissionState.None);
    // Create a SecurityElement instance by calling the ToXml method on the 
    // DnsPermission instance.
    // Print its attributes, which hold the  XML encoding of the DnsPermission
    // instance.
    Console.WriteLine("Attributes and Values of 'DnsPermission' instance :");
    PrintKeysAndValues(permission.ToXml().Attributes);

    // Create a SecurityElement instance.
    SecurityElement securityElementObj = new SecurityElement("IPermission");
    // Add attributes and values of the SecurityElement instance corresponding to
    // the permission instance. 
    securityElementObj.AddAttribute("version", "1");
    securityElementObj.AddAttribute("Unrestricted", "true");
    securityElementObj.AddAttribute("class","System.Net.DnsPermission");
                     
    // Reconstruct a DnsPermission instance from an XML encoding.
      DnsPermission permission1 = new DnsPermission(PermissionState.None);
    permission1.FromXml(securityElementObj);

    // Print the attributes and values of the constructed DnsPermission object.
    Console.WriteLine("After reconstruction Attributes and Values of new DnsPermission instance :");
    PrintKeysAndValues(permission1.ToXml().Attributes);
  }
  catch(NullReferenceException e) 
  {
    Console.WriteLine("NullReferenceException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
  }
  catch(SecurityException e) 
  {
    Console.WriteLine("SecurityException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
  }
  catch(ArgumentNullException e) 
  {
    Console.WriteLine("ArgumentNullException caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
  }
  catch(Exception e)
  {
    Console.WriteLine("Exception caught!!!");
    Console.WriteLine("Source : " + e.Source);
    Console.WriteLine("Message : " + e.Message);
  }
}

private void PrintKeysAndValues(Hashtable myList) {
   // Get the enumerator that can iterate through the hash table.
   IDictionaryEnumerator myEnumerator = myList.GetEnumerator();
   Console.WriteLine("\t-KEY-\t-VALUE-");
   while (myEnumerator.MoveNext())
      Console.WriteLine("\t{0}:\t{1}", myEnumerator.Key, myEnumerator.Value);
      Console.WriteLine();
}