gio:action-group-action-parameter-type (group name)

group -- a g:action-group instance
name -- a string for the name of the action to query

The g:variant-type parameter type.

Queries the type of the parameter that must be given when activating the named action within the action group. When activating the action using the g:action-group-activate-action function, the g:variant-type parameter type given to that function must be of the type returned by this function.

In the case that this function returns nil, you must not give any g:variant parameter, but nil instead.

The parameter type of a particular action will never change but it is possible for an action to be removed and for a new action to be added with the same name but a different parameter type.