I am adding one GtkVBox to GtkViewPort.
And I am doing scrolling for GtkViewPort based on two Up/Down Buttons.

I need to display last item in VBox as we do in Message Chat Screens (Message Chat list displays/adds newest chat message at bottom of the list) i doing exact thing.

so for scrolling at the bottom of the GtkViewPort i am doing in the map event call back.

GtkAdjustment* adjustment;
adjustment = gtk_viewport_get_vadjustment(GTK_VIEWPORT(viewport_list));
gtk_adjustment_set_value(adjustment, gtk_adjustment_get_upper(adjustment));

So this works perfectly fine. it displays newest added widget in Vbox at the end.

on some external events I add new Widgets to my VBox and call above code again to display these newly added widgets. on first add it does not scroll at all but on 2nd add to VBOX it scroll upto 2nd last Widget in the list.

Why this might be happening.
It there another way of scrolling GtkViewPort to the end?

Thanks for reading :)