3 replies to this topic

[williamevanl]

I have a program in c# that basically draws points on the screen. A button causes these points to be drawn. Sometimes and it seems completely random, the points are drawn and then vanish for no reason. Why is this happening and how do I fix it?

[Roger]

Can you post your code?

[zoranh]

You must draw points on Paint event, not just when you wish it. If you do not do that, it may happen that something else triggers the Paint event which in turn paints window background using solid brush - hence your points disappear.

Correct way to draw points on button click is to invoke Invalidate method, specifying the region which should contain points. Once done, OnPaint method will be invoked from inside and there is the place to put drawing code.

[williamevanl]

That sounds helpful ^ But I'm not sure how to do it. Here' my code

private void plotcolor()
        {

            
            Graphics g = this.CreateGraphics();
           // g.Clear(Color.LightGray);
            int points = 0;
            for (points = 0; points <= myarrays.Kmeangroup1x.Count() - 1; points++)
            {
                Size s = new Size(10, 10);
                Point p = new Point((((Convert.ToInt32(myarrays.Kmeangroup1y[points]) * chartvalues.maxwidth) / chartvalues.ymaxvalue) + 50), ((chartvalues.maxheight - (Convert.ToInt32(myarrays.Kmeangroup1x[points]) * chartvalues.maxheight) / chartvalues.xmaxvalue) + 50));

                Rectangle r2 = new Rectangle(p, s);
                Region r = new Region(r2);
                g.FillRegion(Brushes.Red, r);
                g.DrawRectangle(Pens.Black, r2);
                
            }