mi programa metro style

private async void ButtonSave_Click(object sender, RoutedEventArgs e)
        {


            if (TextBoxName.Text.Length <= 2)
            {
                MessageDialog msg = new MessageDialog("Names don't allow 2 or less characters", "Information");
                await msg.ShowAsync();
                return;
            }

            //aqui introduce los datos de los textbox
            //instanciamos la clase Activity
            Activity Activity = new Activity();
            Activity.Name = TextBoxName.Text;
            Activity.Participant = TextBoxParticipant.Text;
            //Activity.Map =
            Activity.Description = TextBoxDescription.Text;
            Activity.Type = TextBoxType.Text;
            Activity.Price = TextBoxPrice.Text;
            Activity.Difficulty = TextBoxDifficulty.Text;
            Activity.Comments = TextBoxComment.Text;

            //serializar el objeto antes de salvarlo con el nombre que queremos


            // aqui ya hacemos el proceso de salvado de datos
            FileSavePicker fileSavePicker = new FileSavePicker();
            //FileSavePicker savePicker = new FileSavePicker();
            fileSavePicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
            // Dropdown of file types the user can save the file as
            fileSavePicker.FileTypeChoices.Add("Activities Documents", new List<string>() { ".act" });
            fileSavePicker.FileTypeChoices.Add("Plain Text", new List<string>() { ".txt" });
            // Default extension if the user does not select a choice explicitly from the dropdown
            fileSavePicker.DefaultFileExtension = ".docx";
            // Default file name if the user does not type one in or select a file to replace
            fileSavePicker.SuggestedFileName = "New Document";
            StorageFile savedFile = await fileSavePicker.PickSaveFileAsync();
            string savedFilePath = savedFile.Path;
            string savedFileName = savedFile.Name;

            // Get the output stream for the SessionState file.
            savedFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(savedFileName, CreationCollisionOption.ReplaceExisting);
            IRandomAccessStream raStream = await savedFile.OpenAsync(FileAccessMode.ReadWrite);
            //StorageFile file = await ApplicationData.Current.LocalFolder.CreateFileAsync("samplefile.dat", CreationCollisionOption.ReplaceExisting);
            //IRandomAccessStream raStream = await file.OpenAsync(FileAccessMode.ReadWrite);

            IOutputStream outStream = raStream.GetOutputStreamAt(0);

            // Serializar objeto a fichero
            //DataContractSerializer serializer = new DataContractSerializer(typeof(Dictionary<string, object>), new DataContractSerializerSettings() { PreserveObjectReferences = true });
            DataContractSerializer serializar = new DataContractSerializer(typeof(Dictionary<string, object>), new DataContractSerializerSettings() { PreserveObjectReferences = true });
            try
            {
                serializar.WriteObject(outStream.AsStreamForWrite(), Activity);
            }
            catch (Exception ex)
            {
                MessageDialog msg = new MessageDialog(ex.Message);
            }
            await outStream.FlushAsync();

        } // fin metodo ButtonSave_Click