Question

Currently my program reads images and text in a record from an xml file, displays them on the screen, and then the click of the previous/next buttons moves to the next record. However, it seems to need a few seconds loading time between each photo and I’d like it to be instant, like how Windows Photo Gallery would…or Facebook photos (bear in mind this is not a web app).

I searched found a few similar situations to mine but none seemed to fit my situation. I tried making a class, based on my search, to deal with background loading and calling it in my program, but it’s fraught with error and probably won’t even do what I want it do:

//ImageManager.cs

class ImageManager
{
    private Dictionary<string, Image> images = new Dictionary<string, Image>();

    public Image get(string s)
    {  // blocking call, returns the image
        return load(s);
    }

    private Image load(string s)
    {  // internal, thread-safe helper
        lock (images)
        {
            if (!images.ContainsKey(s))
            {
                Image img = images.Add(s, img); //load the image s - ERROR cannot implicitly convert type void to image. Void??
                return img;
            }
            return images[s];
        }
    }

    public void preload(params string[] imgs)
    {  // non-blocking preloading call
        foreach (string img in imgs)
        {
            BackgroundWorker bw = new BackgroundWorker();
            bw.DoWork += (s, e) => { load(img); };  // discard the actual image return
            bw.RunWorkerAsync();
        }
    }
}


//MainWindow.cs

ImageManager im = new ImageManager();
im.preload("Data/Images"); // Errors - im is a field but used like a type/token '('

Many thanks in advance

Answer 1

Your ImageManager should work with ImageSources, not Images. Even if you get your current code to work you’ll find that your UI still hangs because you have no choice but to perform the work on the UI thread. If you instead deal with ImageSources, you can load them on a background thread and then freeze them in order to use them from the UI thread. This frees you to pre-emptively load images, or to show a loading animation whilst they load.

BitmapFrame.Create is likely the method you want to be using to load the images.