Question

I’m attempting to store a List (where Show is my class that implements IXmlSerializable) to the local isolated storage. I’m using the code from this page:
http://metrostoragehelper.codeplex.com/
I’ve implemented the change suggested in the Issues section.
I am using the following code to add a Show object when it is clicked from an item list.

private async void addShowButton_Click_1(object sender, RoutedEventArgs e)
    {
        var isoStorage = new StorageHelper<List<Show>>(StorageType.Local);

        List<Show> currentShows = await isoStorage.LoadASync("myShowsEx");
        if(currentShows == null) {
            currentShows = new List<Show>();
        }

        currentShows.Add(currentShow);

        isoStorage.SaveASync(currentShows, "myShowsEx");


        //Read it back, for debugging to check if it has been added properly. 
        List<Show> currentShowsRB = await isoStorage.LoadASync("myShowsEx"); //Exception here

    }

The first show is added perfectly fine and it shows up in the currentShowsRB List. When a second item is clicked and the method above invoked an exception occurs on the last LoadAsync call: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
How can I get around this to access the local data store for multiple calls?

Below is also the relevant code from the StorageHelper:

public async void SaveASync(T Obj, string FileName)
    {

        FileName = FileName + ".xml";
        try
        {
            if (Obj != null)
            {
                StorageFile file = null;
                StorageFolder folder = GetFolder(storageType);
                file = await folder.CreateFileAsync(FileName, CreationCollisionOption.ReplaceExisting);

                using (var writeStream = await file.OpenAsync(FileAccessMode.ReadWrite))
                {
                    Stream outStream = Task.Run(() => writeStream.AsStreamForWrite()).Result;
                    serializer.Serialize(outStream, Obj);
                    //writeStream.Dispose(); //Added and we get UnauthorizedAccessException
                    // outStream.Dispose(); //Added ObjectDisposedException caught in catch statement below
                }
            }
        }
        catch (Exception)
        {
            throw;
        }
    }
    public async Task<T> LoadASync(string FileName)
    {
        FileName = FileName + ".xml";
        try
        {
            StorageFile file = null;
            StorageFolder folder = GetFolder(storageType);
            file = await folder.GetFileAsync(FileName);
            using (var readStream = await file.OpenAsync(FileAccessMode.Read))
            {
                Stream inStream = Task.Run(() => readStream.AsStreamForRead()).Result;
                inStream.Position = 0;
                return (T)serializer.Deserialize(inStream);
            }
        }
        catch (FileNotFoundException)
        {
            //file not existing is perfectly valid so simply return the default 
            return default(T);
            //throw;
        }
        catch (Exception)
        {
            //Unable to load contents of file
            throw;
        }
    }

The writeStream.Dispose() line I added in, but even when this is included I get the same error message of Access is Denied. If I also include the outStream.Dispose() line then I get a ObjectDisposedException being caught in the catch statement right below. Is there something else I should be doing?

Answer 1

You are not waiting for the SaveAsync to finish, trying to Load when the Save is still in progress. Change it to:

//isoStorage.SaveASync(currentShows, "myShowsEx");
await isoStorage.SaveASync(currentShows, "myShowsEx");   

List<Show> currentShowsRB = await isoStorage.LoadASync("myShowsEx"); 

---

Edit, awaiting on void is a standard problem.
The quick fix is :

 await TaskEx.Run(() => isoStorage.SaveASync(currentShows, "myShowsEx"));

But you can also move the TaskEx.Run() inside SaveASync(). And given a name that ends with Async, it should not be void but:

Task SaveASyncT Obj, string FileName)
{ 
    return TaskEx.Run() => { .... }
}

I don’t believe there is an async version of Serialize, so it stays at TaskEx.Run() .