如何在PictureBox C＃中绘制对象？

Question

I trying draw a rectangles in PictureBox by mouse click:

    private void MyPictureBoxMouseClick(object sender, MouseEventArgs e)
    {
        using (Graphics g = MyPictureBox.CreateGraphics())
        {
            var pen = new Pen(Color.Black, 2);
            g.DrawRectangle(pen, e.X, e.Y, 50, 50);

            pen.Dispose();
        }
    }

And rectangles are drawning. But when i move mouse beyond the PictureBox all rectangles are disappear. How to avoid it?

UPDATE
I added a Paint event:

  private List<Rectangle> Rectangles { set; get; }
        private void MyPictureBoxPaint(object sender, PaintEventArgs e)
    {
        using (Graphics g = MyPictureBox.CreateGraphics())
        {
            var pen = new Pen(Color.Black, 2);
            foreach (var rect in Rectangles)
            {
                g.DrawRectangle(pen, rect); 
            }

             pen.Dispose();
        }
    }

    private void MyPictureBoxMouseClick(object sender, MouseEventArgs e)
    {
        Rectangles.Add(new Rectangle(e.X, e.Y, 50, 50));
        MyPictureBox.Refresh();
    }

But now rectangles not drawning.

Update

Oh it was my mistake.

g.DrawRectangle(pen, rect);  -> e.Graphics.DrawRectangle(pen, rect); 

Answer 1

Yes, you're drawing over the picture box. When the next paint messgae arrives, picturebox re-paints itself again at that time it'll overwrite your rectangles.

You either need to draw it in Paint event in order to make your rectangles survive or you can Draw over the PictureBox.Image so it will stay there.

For your edit: You need to use e.Graphics property. For instance following code works for me.

private void MyPictureBoxPaint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    using (var pen = new Pen(Color.Black, 2))
    {
        foreach (var rect in Rectangles)
        {
            g.DrawRectangle(pen, rect);
        }
    }
}