我想在DropdownButtonFormField中显示提示文本。然而，当我向InputDecoration添加提示文本时，它不会显示，因为Getx强制执行初始值。有没有什么方法可以显示提示文本而不是使用Getx的初始值？我需要这个，因为如果用户没有从列表中选择任何城市，我想向他们显示一个警告，而不是接受默认城市作为他们的选择。先谢了。
我的控制器类：

class DropdownMenuController extends GetxController {

      final selectedCity = "Berlin".obs;
      final List<String> cityList = [
       'Berlin',
       'Paris',
       'Rome',
      ];

    void setSelectedCity(String value) {
      selectedCity.value = value;
    }
  }

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视图类：

DropdownMenuController controller = DropdownMenuController();

class InfoDropdown extends StatelessWidget {
  const InfoDropdown({
Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        const Padding(
          padding: EdgeInsets.fromLTRB(10, 2, 10, 2),
          child: Text(
            'City',
            style: TextStyle(
              color: Colors.indigo,
            ),
          ),
        ),
        Padding(
          padding: const EdgeInsets.fromLTRB(10, 2, 10, 20),
          child: SizedBox(
            height: 50,
            child: Obx(() => DropdownButtonFormField(
                  decoration: kDropdownMenuDecoration //There is a hint text here I can't display,
                  onChanged: (newValue) {
                    controller.setSelectedCity(newValue as String);
                  },
                  value: controller.selectedCity.value,
                  items: controller.cityList.map((selectedItem) {
                     return DropdownMenuItem(
                      value: selectedItem,
                      child: Text(
                        selectedItem,
                      ),
                    );
                  }).toList(),
                )),
          ),
        ),
      ],
    );
  }
}

//kDropdownMenuDecoration:
InputDecoration(
  contentPadding: EdgeInsets.fromLTRB(10, 2, 10, 2),
  border: OutlineInputBorder(
    borderRadius: BorderRadius.all(
      Radius.zero,
    ),
  ),
  focusedBorder: OutlineInputBorder(
    borderRadius: BorderRadius.all(
      Radius.zero,
    ),
    borderSide: BorderSide(color: Colors.grey),
  ),
);

型