1. protected
void registerBoolServiceExtension({String name, @required ValueGetter<bool> getter, @required ValueSetter<bool> setter })

Registers a service extension method with the given name (full name "ext.flutter.name"), which takes a single argument "enabled" which can have the value "true" or the value "false" or can be omitted to read the current value. (Any value other than "true" is considered equivalent to "false". Other arguments are ignored.)

Calls the getter callback to obtain the value when responding to the service extension method being called.

Calls the setter callback with the new value when the service extension method is called with a new value.

Source 

@protected
void registerBoolServiceExtension({
  String name,
  @required ValueGetter<bool> getter,
  @required ValueSetter<bool> setter
}) {
  assert(name != null);
  assert(getter != null);
  assert(setter != null);
  registerServiceExtension(
    name: name,
    callback: (Map<String, String> parameters) async {
      if (parameters.containsKey('enabled'))
        setter(parameters['enabled'] == 'true');
      return <String, dynamic>{ 'enabled': getter() };
    }
  );
}