windows phone下进行Isolated的IO读写

using (System.IO.IsolatedStorage.IsolatedStorageFile isf = System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication())
            {
                if (isf.FileExists(fileName))
                {
                    using(System.IO.IsolatedStorage.IsolatedStorageFileStream fs = isf.OpenFile(fileName,FileMode.Open))
                    {
                        Trips = ReadTrips(fs);
                    }
                }
            }