public List<FavoriteItem> FavoriteList = new List<FavoriteItem>();
        public string strFile = "favorite.xml";

        public void saveFavorite()
        {
            try
            {
                //apply for the storage in Silverlight
                using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    string dirPath = "MyDir";
                    if (!store.DirectoryExists(dirPath))
                    {
                        //Create directory
                        store.CreateDirectory("MyDir");
                    }

                    string filePath = Path.Combine("MyDir", strFile);
                    //MessageBox.Show(strFile);
                    if (store.FileExists(filePath))
                    {
                        store.DeleteFile(filePath);
                    }

                    //Serialize using DateContractSerializer
                    IsolatedStorageFileStream fileStream = store.CreateFile(filePath);
                    DataContractSerializer serializer = new DataContractSerializer(typeof(List<FavoriteItem>));
                    serializer.WriteObject(fileStream, FavoriteList);
                    fileStream.Close();

                }
            }
           catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        public List<FavoriteItem> loadFavorite()
        {
            try
            {
                List<FavoriteItem> listHistory;
                using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    string filePath = Path.Combine("MyDir", strFile);
                    if (store.FileExists(filePath))
                    {
                        //Deserialize
                        IsolatedStorageFileStream fileStream = store.OpenFile(filePath, FileMode.Open);
                        DataContractSerializer serializer = new DataContractSerializer(typeof(List<FavoriteItem>));
                        listHistory = (List<FavoriteItem>)serializer.ReadObject(fileStream);
                        fileStream.Close();
                        return listHistory;
                    }
                    else
                    {
                        return null;
                    }

                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
                return null;
            }
        }