Can't find gtk header file for vala-code compilation

Question

I am trying to run the first sample code on this site. Unfortunately I got the following error message:

Package gobject-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gobject-2.0.pc'
to the PKG_CONFIG_PATH environment variable

So I used locate gobject-2.0.pc to find its location and added

export PKG_CONFIG_PATH="/usr/lib/x86_64-linux-gnu/pkgconfig:PKG_CONFIG_PATH"`

at the end of my ~/.bashrc. Now I get the following error message when I try to compile the vala code:

/path/to/foo.vala.c:9:21: fatal error: gtk/gtk.h: No such file or directory
compilation terminated.

I found a gtk.h in /usr/include/gtk-3.0/gtk, but the compiler can't find it apparently. I also noticed that

$ pkg-config --cflags gtk+-3.0

yields

Package xproto was not found in the pkg-config search path.
Perhaps you should add the directory containing `xproto.pc'
to the PKG_CONFIG_PATH environment variable
Package 'xproto', required by 'xau', not found

although xproto.pc is in /usr/share/pkgconfig and the pkg-config man-page lists this as one of standard search paths of pkg-config.

Edit: On the other hand

$ pkg-config --libs gtk+-3.0

yields

-L/usr/lib/x86_64-linux-gnu -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lgobject-2.0 -lglib-2.0

which looks as one would expect. /Edit

Can anyone help me with this?

Cheers

Answer 1

Just had the same issue on elementary OS Hera. I've fixed it by adding this line to my .bashrc:

export PKG_CONFIG_PATH="/usr/share/pkgconfig:/usr/lib/pkgconfig:/usr/lib/x86_64-linux-gnu/pkgconfig:$PKG_CONFIG_PATH"