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

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

The g:variant-type state type, if the action is stateful.

Queries the type of the state of the named action within the action group. If the action is stateful then this function returns the g:variant-type state type of the state. All calls to the g:action-group-change-action-state function must give a g:variant parameter of this type and the g:action-group-action-state function will return a g:variant parameter of the same type.

If the action is not stateful then this function will return nil. In that case, the g:action-group-action-state function will return nil and you must not call the g:action-group-change-action-state function.

The state 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 state type.