In colibri imx6 2.6 b2 . how to install gtk-sharp?

how to install gtk-sharp ?
I installed mono with
“opkg install mono”
but gtk-sharp is missing.

One would require an OpenEmbedded build to add gtk-sharp.

meta-mono layer needs to be added and then gtk-sharp will be available for building. For adding layers, one can see an example here.

Once this is in place, mono and gtk-sharp can be added by first specifying

IMAGE_INSTALL_append = " mono gtk-sharp"

in ~oe-core/build/conf/local.conf file and then building the image.