BitmapEncoder FlushAsync() never returns

Question

I've scoured the web for this and not found a solution yet. I have a DispatchTimer in my Universal phone app. On each tick, I want to capture a portion of the screen and save it to JPEG. My code seems very straightforward, and there are no crashes -- it simply never returns from the FlushAsync(). It seems like it must be a deadlock scenario, but I haven't been able to find where the conflict is yet:

using (var ms = new MemoryStream())
{
    var renderTargetBitmap = new RenderTargetBitmap();
    await renderTargetBitmap.RenderAsync(ctrl);
    var pixelBuffer = await renderTargetBitmap.GetPixelsAsync();

    using (var ras = ms.AsRandomAccessStream())
    {
        var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId, ras, propertySet);

        encoder.SetPixelData(
            BitmapPixelFormat.Bgra8,
            BitmapAlphaMode.Premultiplied,
            (uint) renderTargetBitmap.PixelWidth,
            (uint) renderTargetBitmap.PixelHeight,
            logicalDpi, logicalDpi,
            pixelBuffer.ToArray());

        await encoder.FlushAsync();
    }

    return ms.ToArray();
}

Any help would be great! I've been at this for hours, trying different ways to get it working with no luck.

Answer 1

I figured it out! Turns out you can't just use MemoryStream.AsRandomAccessStream() as your encoder destination. Turns out you should just use the InMemoryRandomAccessStream, then afterwards get the bytes:

byte[] bytes = new byte[ras.Size];
await ras.AsStream().ReadAsync(bytes, 0, bytes.Length);
return bytes;

Not sure why MemoryStream caused the problem it did, but this is a pretty easy fix! I hope this helps someone else.