C++ (Qt)
QFileDialog w;
w.setFileMode(QFileDialog::DirectoryOnly);
QListView *l = w.findChild<QListView*>("listView");
if (l)
l->setSelectionMode(QAbstractItemView::MultiSelection);
QTreeView *t = w.findChild<QTreeView*>();
if (t)
t->setSelectionMode(QAbstractItemView::MultiSelection);
w.exec();