Error: Either zero or 2 or more [DropdownMenuItem]s were detected with the same value I/flutter (18363): 'package:flutter/src/material/dropdown.dart':

I had the exact same error, multiple Dropdowns all feeding from the same static list, the only difference is that in my case, it was a list of Objects, not Strings.

So, if it's a static list, there's no way it's empty, no duplicate values in the list, AND you already make sure value is not empty? Then the only option remaining is that item.value is different than value

In my case, as it was an Object list, I had to overwrite operator == and hashcode methods in my Object class.

bool operator ==(dynamic other) =>
      other != null && other is TimeSelection && this.hour == other.hour;

  @override
  int get hashCode => super.hashCode;

And that was it. I didn't had to initialize _value1 or _value2

This exception you have because of mistakes:

1. No _value1 and _value2 initialization.
2. When you initialize them make sure that _value1 and _value2 right from nameList e.g.

_value1 = nameList[0];
_value2 = nameList[3];

this is important step with complex data type, but in your case

_value1 = "Name1";
_value2 = "Name4";

will be sufficient.

Full example:

  String _value1;
  String _value2;

  final List<String> nameList = <String>[
    "Name1",
    "Name2",
    "Name3",
    "Name4",
    "Name5",
    "Name6",
    "Name7",
    "Name8"
  ];

  /// initialization is here:
  @override
 void initState() {
    super.initState();
    _value1 = nameList[0];
    _value2 = nameList[3];
  }

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: <Widget>[
        Row(
          children: <Widget>[
            Text('Name: '),
            Center(
              child: DropdownButton(
                value: _value1,
                onChanged: (value) {
                  setState(() {
                    _value1 = value;
                  });
                },
                items: nameList.map(
                  (item) {
                    return DropdownMenuItem(
                      value: item,
                      child: new Text(item),
                    );
                  },
                ).toList(),
              ),
            ),
          ],
        ),
        Row(
          children: <Widget>[
            Text('Name: '),
            Center(
              child: DropdownButton(
                value: _value2,
                onChanged: (value) {
                  setState(() {
                    _value2 = value;
                  });
                },
                items: nameList.map(
                  (item) {
                    return DropdownMenuItem(
                      value: item,
                      child: new Text(item),
                    );
                  },
                ).toList(),
              ),
            ),
          ],
        ),
      ],
    );
  }
}

I have the same problem, and I solved it. The dropdown button needs items list and value. We define items and selected items, but the item chosen instance does not inside the items list.

You should try this and fix your logic. (value ıs selected item value for user)

 var _value = itemList.isEmpty
    ? value
    : itemList.firstWhere((item) => item.value == value.value);

More : https://gist.github.com/VB10/fd560694fec0a38751e798a213408001