PaintEvent not overpainting

Question

I have a Windows Forms application in C# with drawing panel and a button - for drawing a line.

When you click the button, you can draw a line for 2 random points.

Answer 1

1. You need to trigger a repaint event after the mouse is let go. Just call drawPanel.Invalidate() to cause the form to be redrawn.

2. To draw multiple lines, you'll have to store the information for each one in a list or something, and draw each line in your repaint. The Paint method basically starts with a blank space each time, so it will only draw the most recent the way you currently have it set up.