gtk:expression-watch (expression object func)

expression -- a gtk:expression intstance
object -- a g:object instance for the argument to watch
func -- a gtk:expression-notify callback function to invoke when the expression changes

The newly installed gtk:expression-watch instance. Note that the only reference held to the watch will be released when the watch is unwatched which can happen automatically, and not just via the gtk:expression-watch-unwatch function.

Installs a watch for the given expression that calls the notify function whenever the evaluation of expression may have changed. GTK cannot guarantee that the evaluation did indeed change when the notify gets invoked, but it guarantees the opposite: When it did in fact change, the notify will be invoked.