Sharing bitmaps?

[trebahl]

I have some images as BitmapFrames produced by PngBitmapDecoder that I would like to display at various places in my UI. I naively thought that I could use a single BitmapFrame instance inside several controls, but when I do that, I get blanks on screen, and it turns out the PixelWidth and PixelHeight of the BitmapFrame become equal to 1, suggesting the object got trashed.

Do you confirm I need to create one BitmapFrame instance per use?

[lindexi]

@trebahl How about share the BitmapSource?

[trebahl]

Err, I don't understand your question. Sharing the bitmapsource is what I'm doing.

[trebahl]

In fact, I've found out that sharing is not even the problem, I can have the same problem with a single control containing the image, so I suppose I'm doing something wrong. My code:

            BitmapFrame img;
            using (var ms = new MemoryStream(Properties.Resources.UnComment)) // a byte array
            {
                var dec = new PngBitmapDecoder(ms, BitmapCreateOptions.None, BitmapCacheOption.Default);
                img = dec.Frames[0];
            }
            var w = new Window()
            {
                Content = new Image() { Source = img }
            };
            Console.WriteLine(img.PixelWidth);  // prints 32
            w.Show();
            Console.WriteLine(img.PixelWidth); // prints 1

[trebahl]

Am I supposed to keep the memory stream alive?

[miloush]

Can you share some demo including the image? I can set two Image controls to the same BitmapFrame without issues.

[trebahl]

The problem disappears if I don't dispose my memory stream. So it seems that the result of decoding the data is not kept in cache despite what the documentation says about BitmapCacheOption.Default.

[miloush]

Sounds like you want BitmapCacheOption.OnLoad.

[trebahl]

Thanks, that works.

But how is one supposed to guess that when the documentation says "Caches the entire image into memory" for BitmapCacheOption.Default? Am I the first person to run into this?

[miloush]

Well it doesn't exactly say when the image is cached, which seems to be the key here. You can see from the values in the documentation that in fact Default = OnDemand.

(WPF's image processing is based on WIC, so sometimes it helps to check the WIC documentation. In this case, you will find out that there is no "Default" in WIC)