c# UWP parallel image loading

Question

I have a C# UWP solution for myself and I have defined the special manifest broadFileSystemAccess, so I can access all files from my PC directly.

Now I'm loading a bunch of image files into memory in order to show them on a GridView. At this task needs a lot of time, I would like to speed it up by running it parallel.

foreach (var item in someList)
{
    BitmapImage bitmapImage = new BitmapImage();

    StorageFile file = await StorageFile.GetFileFromPathAsync(item.ImagePath);
    using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.Read))
    {
        await bitmapImage.SetSourceAsync(fileStream);
    }

    someOtherList.Add(new someModel { ... });
};

On some other thread I found the usage of Parallel.ForEach - but that does not support async calls. Then I saw a library called Dasync with using Dasync.Collections. However using this function just throws an error saying something about an interface that was marshalled for another thread that was called by the application (roughly translated), so I figured that library might not be suitable for this task either.

How would I parallelize this in a C# UWP application?

Answer 1

You could start all tasks and then wait for them all to complete using Task.WhenAll:

Func<Item, Task<BitmapImage>> f = async (item) =>
{
    BitmapImage bitmapImage = new BitmapImage();

    StorageFile file = await StorageFile.GetFileFromPathAsync(item.ImagePath);
    using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.Read))
    {
        await bitmapImage.SetSourceAsync(fileStream);
    }
    return bitmapImage;
};

BitmapImage[] bitmapImages = await Task.WhenAll(someList.Select(f).ToArray());