Flutter 对象类型的值不能分配给SigninCharacter类型的变量

我在做一个单选按钮，然后我会面对这个错误//类型为"Object"的值无法分配给"SigningCharacter"类型的变量.try 更改变量的类型，或将右侧类型转换为"SigningCharacter"\

enum SigninCharacter { fill, outline }

class productOverVeiw extends StatefulWidget {
  const productOverVeiw({Key? key}) : super(key: key);

  @override
  State<productOverVeiw> createState() => _productOverVeiwState();
}

class _productOverVeiwState extends State<productOverVeiw> {
  SigninCharacter _character = SigninCharacter.fill;


Radio(
                                  value: SigninCharacter.fill,
                                  groupValue: _character,
                                  activeColor: Colors.green,
                                  onChanged: (value) {
                                    setState(() {
                                      _character = value ;//A value of type 'Object?' can't be assigned to a variable of type 'SigninCharacter'. Try changing the type of the variable, or casting the right-hand type to 'SigninCharacter'.\
                                    });
                                  })