碰到个头疼无比的silverlight跨域访问WCF的有关问题，MSDN逛了好几圈还是没找到解决方案

 public class SLService : SL.WCF.IServices.ISLService    {        private SL.WCF.SQLProvide.SQLHelp help = new SQLProvide.SQLHelp();        public List<Book> PreviewAllBooks()        {            List<Book> bookLibrary = new List<Book>();            DataTable ds = help.GetBooksInfo();            foreach (DataRow dr in ds.Rows)            {                bookLibrary.Add(new Book { ID = Guid.Parse(dr[0].ToString()), Name = dr[1].ToString(), Count = int.Parse(dr[2].ToString()) });            }            return bookLibrary;        }        public string AddNewBook(Book b)        {            int result = help.AddBook(b.ID, b.Name);            switch (result)            {                case 0:                    return "Fail to add new book: " + b.Name;                case 1:                    return "You have added a new book: " + b.Name;                default:                    return "Unexpect Error: " + result.ToString();            }        }        public string BuyBooks(Book b, int count)        {            int result = help.BuyBook(b.ID, count);            switch (result)            {                case 0:                    return "Fail to buy book: " + b.Name;                case 1:                    return "You have buy " + result.ToString() + " books " + b.Name;                case 2:                    return "You don't select any book to buy";                default:                    return "Unexpect Error: " + result.ToString();            }        }

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<?xml version="1.0" encoding="utf-8" ?><cross-domain-policy>  <allow-access-from domain="*" headers="*"/></cross-domain-policy>

 public partial class DataValidation : UserControl    {        private SLServiceClient ssc = null;        public DataValidation()        {            InitializeComponent();            if (ssc == null)            {                ssc = new SLServiceClient();                ssc.PreviewAllBooksCompleted += new EventHandler<PreviewAllBooksCompletedEventArgs>(ssc_PreviewAllBooksCompleted);            }        }         private void UserControl_Loaded(object sender, RoutedEventArgs e)        {            ssc.PreviewAllBooksAsync();        }        void ssc_PreviewAllBooksCompleted(object sender, PreviewAllBooksCompletedEventArgs e)        {            if (!e.Cancelled && e.Error == null)            {                this.dgView.DataContext = e.Result;                this.dgView.ItemsSource = e.Result;            }        }}