Filechooserbuttons and gtk_widget_set_sensitive

[Roger Matthews <roger matthews hotmail com>]

To someone willing to help,
 
 1) Following the example Listing 4.10 of the GTK+ Development book filechooserbuttons.c I have created a 
filechooser button and label, which are attached to a grid rather than a box. When clicked a "dialogue" 
appears, I can then navigate directories to the filtered files, highlight the selected files, but when 
double-clicked or press 'open', nothing happens. That is, the path/filename is displayed in the label and the 
selected filename is displayed in the button but the file is not opened. How do I open the file?
 
2) I would like to activate/de-activate spinbuttons depending on whether certain other selections have been 
made (with other integer spinbuttons). I have tried using gtk_widget_set_sensitive ( GtkWidget *widget, 
gboolean sensitive) but get compilation warning: unknown type name 'gtk_widget_set'. I'm using GTK3. Any 
clues? 
 
3) I've built a GUI coded in C without using a builder.ui file and would like to make it into a stand-alone 
application, preferably all 'hand' coded, how do I do this? I'm having difficulty following the example in 
the documentation because it uses a buider.ui file, I am unsure of the form of the main() format, and I can't 
locate https://git.gnome.org/browse/gtk+/tree/examples/application2/exampleappwin.c 
 
Thanks,
Roger Matthews