title: Qt TableView show big file with unknown row count
body: <p>i want to show huge files line per line in a TableView! to speed up loading the file will not be loaded at once. the current approch is i calculate a average rowscount with a few steps thru the file. now when i scroll thru the view i will load the content on demand. i hold a cache for up and down scrolling so eq. when i scroll to eq. to a position witch is not in the cache or to far from it the cache will cleared and this one entry will be added. so now i can scroll to any position in the file and can also scroll linewise or pagewise because this will be always calculaed from the front/back cash entries.
  problem is now when i scroll stepwise from an row so it can be that the row in tableview is now 50 but the right row in the file is 70 now i will scroll stepwise back then when i am on row 1 the file row ist 20. same problem is also on the end. </p>