public ClsLogs(Form frmmain) {
            _frmmain = frmmain;
        }

        public void Logs(string ex)
        {

            ListBox ls= _frmmain.Controls["listbox1"] as ListBox;
            if (ls != null) ls.Items.Add("Log->" + ex);
           
        }

i dont have any idea about it;i think my path is not true;but i try it:

ListBox ls=null;
ls= _frmmain.Controls["listbox1"] as ListBox;
if (ls != null) ls.Items.Add("Log->" + ex);