graphics - Draw lines on a picturebox using mouse clicks in C# -

i'm trying make program draw lines on picturebox using mouse clicks locations of line drawn , to. current code:

public partial class form1 : form {     int drawshape;      private point p1, p2;     list<point> p1list = new list<point>();     list<point> p2list = new list<point>();      public form1()     {         initializecomponent();         picturebox1.image = new bitmap(picturebox1.width, picturebox1.height);     }      private void button1_click(object sender, eventargs e)     {         drawshape = 1;     }      private void button2_click(object sender, eventargs e)     {         drawshape = 2;     }      private void picturebox1_mousedown(object sender, mouseeventargs e)     {         if (drawshape == 1)         {             if (p1.x == 0)             {                 p1.x = e.x;                 p1.y = e.y;             }             else             {                 p2.x = e.x;                 p2.y = e.y;                  p1list.add(p1);                 p2list.add(p2);                  invalidate();                 p1.x = 0;             }         }     }      private void picturebox1_paint(object sender, painteventargs e)     {         graphics g = graphics.fromimage(picturebox1.image);         if (drawshape == 1)         {             using (var p = new pen(color.blue, 4))             {                 (int x = 0; x < p1list.count; x++)                 {                     g.drawline(p, p1list[x], p2list[x]);                 }             }         }     } 

at moment doesn't allow me draw on picturebox @ all. how possible?

change invalidate(); picturebox1.invalidate();