I found this code on my machine:
Qt Code: 
  1. // In constructor...
  2.     root = dirModel->index(QDir::currentPath());
  3.     listView->setRootIndex(root);
  4.  
  5. // later...
  6. void MainWindow::up_button_clicked()
  7. {
  8.     root = root.parent();
  9.     listView->setRootIndex(root);
  10. }
  11.  
  12. void MainWindow::listview_double_clicked(QModelIndex index)
  13. {
  14.     if (static_cast<const QDirModel *>(index.model())->isDir(index))
  15.     {
  16.         root = index;
  17.         listView->setRootIndex(root);
  18.     }
  19.     else
  20.     {
  21.         // do something with clicked file.
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