大家帮我看看

这样试试
procedure TForm1.Button1Click(Sender: TObject);
var  mystream:tmemorystream;  
       tmpstr,computername:string;  
       i:integer;  
begin
computername:='ddl';
listbox1.items.Add('ddl');
istbox1.ItemIndex:=0;
if  edit1.text<>''
then
   begin
       nmudp1.ReportLevel:=status_basic;  
       nmudp1.localport:=8888;  
       nmudp1.remoteport:=8888;
       if  listbox1.items[listbox1.ItemIndex]=computername  
       then  memo1.lines.add(computername+'say  to  himself'+edit1.text)  
       else  memo1.lines.add(computername+'say  to'+listbox1.Items[listbox1.itemindex]+edit1.text);  
       tmpstr:=edit1.text;  
       //mystream.create;  
       mystream  :=TMemoryStream.Create;    
       //try  
       MyStream.Write(TmpStr,Length(Edit1.Text));  
       if  listbox1.itemindex=0  
       then  
           begin  
               for  i:=1  to  listbox1.items.count-1  do  
               begin  
               nmudp1.remotehost:=listbox1.items[i];  
               nmudp1.sendstream(mystream);  
               end  
           end  
       else  
           begin  
           nmudp1.remotehost:=listbox1.Items[listbox1.itemindex];  
           nmudp1.sendstream(mystream);  
           end;  
       //finally  
       //mystream.free;  
       //end;  
       edit1.text:='';  
       edit1.setfocus;  
   end  
else  edit1.setfocus;   
end;