SimpleAction.addOnChangeState

Indicates that the action just received a request to change its state.

value will always be of the correct state type, i.e. the type of the initial state passed to SimpleAction.newStateful. If an incorrect type is given when requesting to change the state, this signal is not emitted.

If no handler is connected to this signal then the default behaviour is to call SimpleAction.setState to set the state to the requested value. If you connect a signal handler then no default action is taken. If the state should change then you must call SimpleAction.setState from the handler.

An example of a 'change-state' handler:

static void
change_volume_state (GSimpleAction *action,
GVariant      *value,
gpointer       user_data)
{
gint requested;

requested = g_variant_get_int32 (value);

// Volume only goes from 0 to 10
if (0 <= requested && requested <= 10)
g_simple_action_set_state (action, value);
}

The handler need not set the state to the requested value. It could set it to any value at all, or take some other action.