UI线程上BitmapImage操作的替代方法？

Question

I would like to create a worker class that can retrieve laggy resources (eg from a database or over a network), and prepare them for later, zero-lag display on the UI. That worker class should not be bound to the UI or to the UI thread ie it should be able to run anywhere. When done, it's output will be a populated array of some image container class that the UI can work with easily.

My first thought was to use the BitmapImage class as the image container; however that inherits from the DependencyObject class, which will restrict access from any non-UI thread. As @Filip pointed out in my earlier form of this question, this is not inherently a problem, but it would restrict the generality of my worker class.

Is there a better Windows class that I can use as the basis for the image container, and then convert to BitmapImage on the UI thread at bind time? Or a better way altogether? Here is some pseudo code to indicate what I'm trying to do, using an array of URIs for the source images.

In the worker class

ImageContainerClass[] prepImages(Uri[] uriSet)
{
    ImageContainerClass[] iccSet = new ImageContainerClass[uriSet.Length];
    for (int i = 0; i < iccSet.Length; i++)
        iccSet[i] = new ImageContainerClass.retrieveImage(uriSet[i]); 
    return iccSet;
} 

On the UI thread (at some later time):

BitmapImage bmi = new BitmapImage();
var image = iccSet[i].getImage();
<<some operation to set the source of bmi to the image>>
someImage.Source = bmi;

Answer 1

I think loading images into BitmapImage happens on a background thread in the platform, so there shouldn't be a need for you to do it. You could probably use BitmapDecoder on a background thread if you needed to and then maybe push a pixel buffer into a WriteableBitmap , but you wouldn't gain much from it. If you really want to force all the code to a background thread then you can use DirectX interop and have a completely separate background render thread for your stuff.

Answer 2

OK, so here's a solution that appears to work.

The following code will run happily on a non-UI thread:

    internal async Task<InMemoryRandomAccessStream> getImage(Uri uri)
    {
        try {
            var httpClient = new HttpClient();
            IBuffer iBuffer = await httpClient.GetBufferAsync(uri);
            byte[] bytes = iBuffer.ToArray();
            InMemoryRandomAccessStream ims = new InMemoryRandomAccessStream();
            DataWriter dataWriter = new DataWriter(ims);
            dataWriter.WriteBytes(bytes);
            await dataWriter.StoreAsync();
            ims.Seek(0);
            return ims;
        } catch (Exception e) { return null; }
    }

Then, the following code may be executed on the UI thread when the image needs to be displayed:

BitmapImage bmi = new BitmapImage();
bmi.SetSource(ims);
someImage.Source = bmi;

I'm sure this can be cleaned up by people more familiar with the relevant frameworks, but hopefully this will help others. My thanks to @Filip for putting me on the right track.