DropdownButton 在 Flutter 中无法正常工作

Question

Am new to Flutter Development. Am populating a snapshot data received from API in DropdownButtonlist. everything works fine. but when I change the items in the list I get above error. am not sure which one is causing the pbm. i surfed the.net a lot but could not find the solution. I get the error even if I have one item in the list. I get error "Error: Either zero or 2 or more [DropdownMenuItem]s were detected with the same value in flutter " Thanks in advance

FutureBuilder(
              future:Api.getSchemes(context),
              builder: (BuildContext context, AsyncSnapshot snapshot) {
                return snapshot.hasData
                    ? Container(
                  padding: EdgeInsets.all(5),
                    decoration: BoxDecoration(
                      color: Color(0xffF3D876),
                      borderRadius: BorderRadius.circular(10),
                    ),

                  child: DropdownButton<ClsSchemes>(
                    alignment: AlignmentDirectional.centerStart,
                    isExpanded: true,
                    value: dropDownValue,
                    hint: Text(dropDownValue.Scheme_Name ?? 'Make a selection'),
                    items: snapshot.data.map<DropdownMenuItem<ClsSchemes>>((item) {
                      return DropdownMenuItem<ClsSchemes>(

                        value: item,
                        child: Text(item.Scheme_Name),
                      );
                    }).toList(),
                    onChanged: (value) {
                      setState(() {
                        dropDownValue = value!;
                        TotalDues = value.Total_Dues;
                      });
                    },
                  ),
                )
                    : Container(
                  child: Center(
                    child: Text('Loading...'),
                  ),
                );
              },
            ),

Answer 1

Since you are using an instance of ClsSchemes as your value, you need to make sure that operator == actually works properly for your class.

For this you need to override the == operator and the hashCode :

Example take from here

class Example {
  final int value;
  Example(this.value);

  @override
  bool operator ==(Object other) =>
      other is Example &&
      other.runtimeType == runtimeType &&
      other.value == value;

  @override
  int get hashCode => value.hashCode;
}

You need to find out what the identifying value of your class is. When are two of those classes equal?

If you already have specific fields that are your "identity" fields, the package equatable makes it a little easier.