c# - Invalidate and DrawRectangle don't work together -

imagine simple .net 2.0 windows-form multilinetextbox fills whole form. want (re-)draw rectangle everytime key pressed. in real application there fare more logic position , stuff of rectangle - keep simple.

i thought: "lets first invalidate textbox , draw rectangle." doesnt work. screen flickers shortly - thats it. if remove line "invaliate" rectangle drawn - old ones keep position..

whats wrong? , how repaint scratch?

thank in advance answers!

private void onkeydown(object sender, keyeventargs e) {         textbox1.invalidate();          using (graphics g = this.textbox1.creategraphics())         {             int startx = 100;             int starty = 300;             int height = 200;              brush brush = new solidbrush(color.fromargb(60, 255, 0, 0));              pen mypen = new pen(color.black, 2);             mypen.dashstyle = dashstyle.dash;              g.drawrectangle(mypen, startx, starty, this.textbox1.width, height);              g.fillrectangle(brush, startx, starty, this.textbox1.width, height);         } } 

your approach flawed. invalidate() requests repaint delayed , happens after draw rectangle. disappears again immediately.

a short (but wrong) fix replace invalidate() update(), don't that.

you'll have move drawing logic textbox1.paint event. , form needs (boolean) property decide whether draw rectangle or not.

your keydown should like:

private void onkeydown(object sender, keyeventargs e) {     this.drawrect = true;     textbox1.invalidate(); }