How to draw on Control so drawing doesn't disappear?

问题

I want to display graphic file in PictureBox I have:

private void btnLoad_Click(object sender, EventArgs e)
{
    if (dgOpenFile.ShowDialog() == DialogResult.OK)
    {
        Bitmap img = new Bitmap(dgOpenFile.FileName);
        picture.Width = img.Height;
        picture.Height = img.Height;
        g.DrawImage(img, 0f, 0f);
    }
}

That's g

private void Form1_Load(object sender, EventArgs e)
{
    g = picture.CreateGraphics();
}

But when I move my Form outside the window my picture disappears. How can I prevent that?

回答1:

You should do any custom drawing in the OnPaint event of the control to make it persistent. This causes your drawing to be redrawn every time the control is painted.

However, in this case it would be easier to use the picture box as it was designed:

picture.Image = img;

回答2:

Windows uses a Paint-on-Request principle.

So when it sends a WM_PAINT message to your Control, it's OnPaint() is called. You should be ready to draw the image (again) in an overridden OnPaint() or in a Paint event handler.

But a Picturebox will do all this for you.

来源：https://stackoverflow.com/questions/4593290/how-to-draw-on-control-so-drawing-doesnt-disappear