drawing - C# Draw Line OnPaint() vs CreateGraphics()

Question

Question: How do you properly draw on a winform from a method other than the OnPaint() method?

Additional Information: The code I have now draws some background lines for a TicTacToe game in the OnPaint() method. Then I use the Mouse_Click event and am running this code which apparently is not proper:

private void TicTacToe_MouseClick(object sender, MouseEventArgs e)
   Graphics g = this.CreateGraphics();
   g.DrawEllipse(this.penRed, this.Rectangle);

For reasons I do not understand, it does draw the circle, but when minimizing or moving the form off screen it erases the circles but not the lines from the OnPaint() method.

Answer 1

You are doing a lot of "view" but no "model".

When you want to create a shape, when the mouse button goes down/up, create some DATA representing the shape.

Your data structures represent the persistent information (it is the data that allows you to save and load this information between sessions).

All your paint function needs to do is look at the DATA structures and paint it. This will therefore persist between sizing/hiding/showing.