vb.net - vb (output is doubling in Richtextbox field) -

using vb in visual studio 2012. can't figure out how clear whatever need clear.

see code i'm using below:

private sub button2_click(byval sender system.object, byval e system.eventargs) handles button2.click      if richtextbox1.text > ""         pingproc.canceloutputread()         'need clearing code here         richtextbox1.text = ""     end if     me.height = 522      pingproc.startinfo         .filename = "cmd.exe"         .arguments = "/c c:\tracert.bat"         .redirectstandardinput = true         .redirectstandardoutput = true         .useshellexecute = false         .createnowindow = true     end      addhandler pingproc.outputdatareceived, addressof handleprocessoutput      pingproc.start()     pingproc.beginoutputreadline()  end sub  private sub handleprocessoutput(byval sender object, byval e system.diagnostics.datareceivedeventargs)     me.invoke(new delegateaddtext(addressof addtext), new object() {e.data}) end sub  delegate sub delegateaddtext(byval text string) private sub addtext(byval text string)     richtextbox1.text &= text & vbcrlf end sub 

now when run code, runs fine. have run second time or more. when end double or more copies depending how many times run code.

first run:

performing trace route 198.224.169.244 tracing route 244.sub-198-224-169.myvzw.com [198.224.169.244] on maximum of 30 hops: 

second run:

performing trace route 198.224.169.244 performing trace route 198.224.169.244 tracing route 244.sub-198-224-169.myvzw.com [198.224.169.244] tracing route 244.sub-198-224-169.myvzw.com [198.224.169.244] on maximum of 30 hops: on maximum of 30 hops: 

might caused addhandler ... so, can try ..

dim handled boolean  if not handled    addhandler pingproc.outputdatareceived, addressof handleprocessoutput   handled = true end if