图片框上的C＃绘图，不是持久的

Question

I have a List<> object, "imagelist", that contains the paths of many images such as .png's. Now, with the following code:

private void paint_picture(PictureBox picture, string pathofpic)
    {
        Graphics g = picture.CreateGraphics();
        Bitmap drawnpic = null;
        if (imagelist.ContainsKey(picture.Name))
        {
            drawnpic = new Bitmap(pathofpic);
            g.DrawImage(drawnpic, 0, 0, picture.Size.Width, picture.Size.Height);
            imagelist[picture.Name] = pathofpic;
        }
        drawnpic.Dispose();
        g.Dispose();
    }

I call this every time the card's image is changed, but I can't seem to make the image persist on the picturebox, when I drag the picturebox across the form (for example, over other pictureboxes). The click and drag code is just moving the picturebox with the mouse, not really relevant.

I've tried invalidating the form when I de-select the image, but it doesn't do anything.

Is there something I'm missing? Screenshot below, I dragged one image around the form and it overwrote the other images it moved across:

Answer 1

That's how painting works – you have to handle its Paint event and keep painting the same thing each time it needs repainting.

What you can do is draw on top of your original image:

Bitmap b = new Bitmap(picture.Image);

using (Graphics g = Graphics.FromImage(b)) {
    using (Bitmap drawnpic = new Bitmap(pathofpic)) {
        g.DrawImage(drawnpic, 0, 0, b.Width, b.Height);
    }
}

picture.Image = b;

Then you'd save the original image somewhere and probably use it instead of picture.Image in the new Bitmap line.

And PascalCase for method names, please. ;)