Public Property ViewFields As String

Dim instance As SPQuery
Dim value As String

value = instance.ViewFields

instance.ViewFields = value

public string ViewFields { get; set; }

Dim webSite As SPWeb = SPContext.Current.Site.AllWebs("Site_Name")
Try
     Dim list As SPList = webSite.Lists("List_Name")

    Dim query As New SPQuery()
    query.ViewFields = "<FieldRef Name='Field1'/>" + _
        "<FieldRef Name='Field2'/>"
    Dim items As SPListItemCollection = list.GetItems(query)

    Dim item As SPListItem
    For Each item In  items
        Response.Write((SPEncode.HtmlEncode(item.Xml) + "<BR>"))
    Next item
Finally
    webSite.Dispose()
End Try 

using (SPWeb oWebsite = SPContext.Current.Site.AllWebs["Site_Name"])
{
    SPList oList = oWebsite.Lists["List_Name"];

    SPQuery oQuery = new SPQuery();
    oQuery.ViewFields = "<FieldRef Name='Field1'/>" +
        "<FieldRef Name='Field2'/>";
    SPListItemCollection colListItemsAvailable = 
      oList.GetItems(oQuery);

    foreach (SPListItem oListItemAvailable in colListItemsAvailable)
    {
        Response.Write(SPEncode.HtmlEncode(oListItemAvailable.Xml) + 
          "<BR>");
    }
}