WPF BitmapFrame and multiple threads

Question

I have a PNG file stored in my cloud in blob storage, I want to download it and render it on the screen in WPF.

I know about the Dispatcher and Freezing, but nothing is working. I keep getting the error about "another thread owns it".

Here is what I have:

var decoder = GetDecoder("http://address/image.png");

Dispatcher.Invoke(DispatcherPriority.Send, new Action<BitmapFrame>(SetImage), decoder.Frames[0]);

public void SetImage(BitmapFrame source)
{
    var bitmapFrame = BitmapFrame.Create(source);  //ERROR HERE!!!!!!!!
    LazyImage.Source = bitmapFrame;
}

private BitmapDecoder GetDecoder(object uri)
{
    var extension = System.IO.Path.GetExtension((string)uri);
    BitmapDecoder decoder = null;
    if (extension.ToLower() == ".png")
        decoder = BitmapDecoder.Create(new Uri((string)uri, UriKind.Absolute), BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.OnLoad);
    return decoder;
}

If i try to freeze the Frame[0] I get an exception saying that this Frame cannot be frozen. Also the Decoder returned by BitmapDecoder.Create is not a PngBitmapDecoder but a LateBoundBitmapDecoder which I dont really know how to use effectively.

Answer 1

In brief: try wrapping the result into a WriteableBitmap .

Long story, with code.

Answer 2

Its possible that you need to not only create the Bitmapframe on the dispatcher but also the BitmapDecoder? Have you tried invoking the GetDecoder on the dispatcher?

Answer 3

This is still a problem today! Wrapping the data in WriteableBitmap as suggested by Bohdan will work, but that type has a front and back buffer which doubles its memory footprint. CachedBitmap is a better choice.

new CachedBitmap(bitmapSource, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);

Use BitmapCacheOption.OnLoad unless you like surprises, and remember to freeze the resulting object too.