c# - InvalidArgument exception on remove of item -

i have listbox1 in items collected.

a timer1 start button1 click.

and progressbar1

here complete code.

private void button1_click(object sender, eventargs e) {     timer1.enabled = true;     timer1.interval = 500;     progressbar1.maximum = listbox1.items.count; }  private void timer1_tick(object sender, eventargs e) {     x.send("<iq type='set' to='" + textbox6.text + "@conference.jabber.com'>" +             "<query xmlns='http://jabber.org/protocol/muc#admin'>" +            "<item jid='" + listbox1.items[0].tostring() +             "@nimbuzz.com' affiliation='member'/></query></iq>");     listbox1.items.removeat(0);     progressbar1.value += 1;     groupbox4.text = listbox1.items.count.tostring(); } 

the code above runs when 0 item left in listbox1 progressbar1 stops there comes , error

system.argumentoutofrangeexception unhandled message: invalidargument=value of '0' not valid 'index'. parameter name: index

how simple check

if (listbox1.items.count > 0) {     listbox1.items.removeat(0); }