c# - How to draw a rectangle on a button click? -

i want when click button, add 1 rectangle form
can add in form paint how want can't add shape rectangle click button , searched didn't find solution it
here know how it?

this code in form paint

    private void form1_paint(object sender, painteventargs e)     {             locationx = locationx + 20;             locationy = locationy + 20;             e.graphics.drawrectangle(pens.black,                         new rectangle(10 + locationx, 10 + locationy, 50, 30));     } 

and 1 button code

    private void button1_click(object sender, eventargs e)     {         this.paint += form1_paint;     } 

but not working when click button. why not working?

the line

 this.paint += form1_paint; 

associate event paint of form function form1_paint. it doesn't trigger it. want 1 time, not everytime hit button.

to trigger paint event, usual way call invalidate() method of form class. in fact, invalidate method of control. form derivate control, have access method in form too.

so right way trigger repaint in windows forms put subscribe in load method :

private void form1_load(object sender, eventargs e) {     this.paint += form1_paint; } 

it should hidden in auto generated code. method form1_paint ok.

finally, button click method should :

private void button1_click(object sender, eventargs e) {     this.invalidate(); // force redraw form } 

from doc :

invalidate() : invalidates entire surface of control , causes control redrawn.

edit :

with method, can draw 1 rectangle @ time, because whole surface redrawn, surface completly erase, , draws asked in form1_paint method.

for answer on how draw multiple rectangles, should create list of rectangle. @ each click button, add rectangle list, , redraw rectangles.

list<rectangle> _rectangles = new list<rectangle>(); private void button1_click(object sender, eventargs e) {     locationx = locationx + 20;     locationy = locationy + 20;     var rectangle = new rectangle(locationx, locationy, 50, 30));     this._rectangles.add(rectangle);     this.invalidate(); // force redraw form }  private void form1_paint(object sender, painteventargs e) {     foreach(var rectangle in this._rectangles)     {         e.graphics.drawrectangle(pens.black, rectangle);     } }