vb.net - VB How to Limit Line number of RichTextBox -

i have problems richtextbox.i have limit rtb's sizes regarding required character number(10 height 10 width).i tried limit number of lines using maxlength property.i mean can limit line length e.g. 10 if define max length 100 there can 10 lines.everything ok without enter key. when press enter not count rest of current line.if press enter after 6th char of line skips next line. , count previous line 6.so box gets longer through downwards. in advance...my code below.

private sub textbox1_keydown(byval sender object, byval e system.windows.forms.keyeventargs) handles richtextbox1.keydown     'here im trying count character number of each line      dim count integer = 0     each s string in me.richtextbox1.lines         count = count + 1         msgbox(count)          dim nextlinetext string = s          if e.keycode = keys.enter             if count < (takefromcombo(combobox1))                 richtextbox1.maxlength = richtextbox1.maxlength - (takefromcombo(combobox1) - nextlinetext.length)             end if         end if          'i tried disable enter key @ last line         if count = takefromcombo(combobox1)             if e.keycode = keys.enter                 e.handled = true             end if         end if     next  end sub 

how this? (where rtb1 richtextbox):

private sub rtb1_keydown(sender object, e keyeventargs) handles rtb1.keydown     if rtb1.text.length > 0         if rtb1.lines.count = 11             e.suppresskeypress = true         end if         if rtb1.lines(rtb1.getlinefromcharindex(rtb1.getfirstcharindexofcurrentline)).length > 9 , e.keycode <> keys.return             e.suppresskeypress = true         end if     end if end sub 

the tools manipulating situation little crude. getfirstcharindexofcurrentline returns character index within entire string of rtb text. getlinefromcharindex(i) gets index of line of text contains i. lines() returns array of lines (which text of rtb, split on carriage returns, , lines(i), array, returns member of array @ index (found using 2 described rtb methods).