There should be exactly one item with [DropdownButton]'s value: false. Either zero or 2 or more [DropdownMenuItem]s were detected with the same value

Question

I am unable to resolve this error. I have implemented a custom drop down and it generate this error

 
 DropDownWidget(
                          list: ["Patient","HouseholdMember","Communityrepresentative","Other"],
                          data: whofollowUp,
                          hint: getTranslated(context, "select"),
                          heading: getTranslated(context, "followup_patient"),
                        ),

the custom drop down that is generating this error and I don't have the option to use the default one that comes with flutter

class DropDownWidget extends StatelessWidget {
  final ValueNotifier<dynamic> data;
  final String heading;
  final List<String> list;
  final String hint;
  final bool showPadding;
  final Color outlineColor;
  final Function onChange;
  final bool isDecode;


  DropDownWidget(
      {Key key,
      this.data,
      this.heading,
      this.list,
      this.outlineColor = const Color(0xffC4C4C4),
      this.hint,
      this.onChange,
      this.isDecode = false,
      this.showPadding = true})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Padding(
          padding: const EdgeInsets.only(bottom: 8.0, left: 8),
          child: Text(
            heading,
            style: TextStyle(
                color: AppColor.primarypurple,
                fontSize: 14,
                fontWeight: FontWeight.w500),
          ),
        ),
        Container(
          height: 40,
          padding: EdgeInsets.only(left: 8, right: 8),
          width: ResponsiveSize.sizeWidth(context),
          decoration: BoxDecoration(
              color: AppColor.backGrey,
              borderRadius: BorderRadius.circular(10),
              border: Border.all(width: 2, color: AppColor.darkBlue)),
          child: ValueListenableBuilder(
            valueListenable: data,
            builder: (ctx, value, child) => DropdownButtonHideUnderline(
              child: DropdownButton(
                  isExpanded: true,
                  items: list.map((var val) {
                    return new DropdownMenuItem(
                      value:
                          isDecode ? ((jsonDecode(val))["id"]).toString() : val,
                      child: new Text(
                       isDecode ?  ((jsonDecode(val))["name"]).toString(): val,
                        maxLines: 1,
                        overflow: TextOverflow.ellipsis,
                        style: TextStyle(
                            fontSize: 14,
                            color: AppColor.primaryColor,
                            fontWeight: FontWeight.w600),
                      ),
                    );
                  }).toList(),
                  // hint: Text(
                  //   hint,
                  //   maxLines: 1,
                  //   overflow: TextOverflow.ellipsis,
                  //   style: TextStyle(
                  //       fontSize: 14,
                  //       color: AppColor.darkBlue,
                  //       fontWeight: FontWeight.w400),
                  // ),
                  value: value,
                  icon: Icon(
                    Icons.keyboard_arrow_down,
                    color: AppColor.darkBlue,
                  ),
                  onChanged: onChange == null
                      ? (newVal) {
                          data.value = newVal;
                        }
                      : (newVal) {
                          data.value = newVal;
                          onChange();
                        }),
            ),
          ),
        ),
        const SizedBox(
          height: 15,
        )
      ],
    );
  }
}

This is a custom drop down which I am trying to use it in my class and it is giving this error which I am unable to resolve

Answer 1

It seems that you have a repetitive (or no matched) value for your dropdown items. One of these 4 solutions would be helpful (check them as follow):

1. recheck and be sure that your elements' id does not be equal here:

value:isDecode ? ((jsonDecode(val))["id"]).toString() :val,

2. maybe isDecode is false and you have a REPETITIVE element in your list!
3. finally, the last possibility can be the value of the value parameter. In the other words maybe it does not match with any item's value:

value: value,

check it out and let me know the result.