Ok, here is the c# managed code equivalent.
public void btnSelPartNum_Clicked(object sender, ClickedEventArgs e)
{XPathNavigator root = MainDataSource.CreateNavigator();
XPathNavigator container = root.SelectSingleNode("/my:travelRequest/my:group1/my:Row[position() = /my:travelRequest/my:CurrentRow]/my:ExtPartNum", ...