Watch the given `expression` for changes.
The notify function will be called whenever the evaluation of `self` 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.
| this |
a `GtkExpression` |
| this_ |
the `this` argument to watch |
| notify |
callback to invoke when the expression changes |
| user_data |
user data to pass to the `notify` callback |
| user_destroy |
destroy notify for `user_data` |
|
The newly installed watch. 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 [[email protected]]. You should call [[email protected]] if you want to keep the watch around. |