gio:action-parameter-type (object)

object -- a g:action object
vtype -- a g:variant-type parameter type

The accessor for the parameter-type slot of the g:action class queries the type of the parameter that must be given when activating the action. When activating the action using the g:action-activate function, the g:variant parameter given to that function must be of the type returned by this function.

In the case that this function returns a nil value, you must not give any g:variant parameter, but a cffi:null-pointer value instead.