Returns the icon name of the button.
If the icon name has not been set with [method@Gtk.Button.set_icon_name] the return value will be null. This will be the case if you create an empty button with [ctor@Gtk.Button.new] to use as a container.
this |
A `GtkButton` |
The icon name set via [method@Gtk.Button.set_icon_name] |