How to get the height of the gtktreeview header?

I've looked in the gtk source code and the header height is private. I've tried something but it didn't work as wanted (the heightWithHeader is 1?!)

Glib::RefPtr<Gdk::Window> pWindow = treeView.get_bin_window();

treeView.set_headers_visible(true);
pWindow->get_size(width, heightWithHeader);

treeView.set_headers_visible(false);

pWindow->get_size(width, heightWithoutHeader);

r_treeView.set_headers_visible(true);

returnValue = heightWithHeader - heightWithoutHeader;

Can you help me with another solution or a fix to my code?

Update: I have to adjust the height of the treeview to display a fixed number of rows. I do this by adjusting the size of the container (a scrolledwindow) to headerHeight + numberRowsToDisplay * heightOfRow.

Solution

The reason your code doesn't work is very probably that you're being "too impatient", not giving GTK+ time to do the redraw of the widgets before you make the headers invisible again.

GTK+ doesn't draw immediately when you do a call that requires a redraw. Instead redraws are queued, and then done all at once from the GTK+ main loop. This way, doing two changes to widgets in sequence does not cause two redraws, but only one.

It's a bit of a hack, but you could try the "classic" GTK+ event-flushing trick, by inserting a loop like this after you turn on the headers:

while(gtk_events_pending())
  gtk_main_iteration();

This simply loops for as long as there are events in GTK+'s queue (the draw changes mentioned above are events, internally), and flushes them, then gives control back to you. This will very probably result in some visual flicker, though.