正しいStorageFolderApplicationData.Current.RoamingFolderを使用してください
public static class RoamingStorage<T> {
public static async void SaveData(string filename, T data)
{
try
{
StorageFile file = await ApplicationData.Current.RoamingFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
using (IRandomAccessStream raStream = await file.OpenAsync(FileAccessMode.ReadWrite))
{
using (IOutputStream outStream = raStream.GetOutputStreamAt(0))
{
DataContractSerializer serializer = new DataContractSerializer(typeof(List<Item>));
serializer.WriteObject(outStream.AsStreamForWrite(), data);
await outStream.FlushAsync();
}
}
}
catch (Exception exc)
{
throw exc;
}
}
public static async System.Threading.Tasks.Task<T> LoadData(string filename)
{
T data = default(T);
try
{
StorageFile file = await ApplicationData.Current.RoamingFolder.GetFileAsync(filename);
using (IInputStream inStream = await file.OpenSequentialReadAsync())
{
DataContractSerializer serializer = new DataContractSerializer(typeof(T));
data = (T)serializer.ReadObject(inStream.AsStreamForRead());
}
}
catch (FileNotFoundException ex)
{
throw ex;
}
catch (Exception ex)
{
throw ex;
}
return data;
}
}
呼び出し例
RoamingStorage<List<Item>>.SaveData(FILENAME,Items);
List<Item> data = await RoamingStorage<List<Item>>.LoadData(FILENAME);