无法使用 Flutter 中的对象列表创建 DropdownButton

Question

This is the error I have got:

Here is my DropdownButton code:

DropdownButton countryPicker() {
    return DropdownButton<String>(
      onChanged: (value) {
        setState(() {
          country = value;
        });
      },
      value: country,
      hint: Text(country),
      items: countries(),
    );
  }

  List<DropdownMenuItem<String>> countries() {
    List<DropdownMenuItem<String>> list = [];
    countryDetails.forEach((c) {
      list.add(DropdownMenuItem<String>(
        child: Text(c.countryName),
        value: c.countryName,
      ));
    });
    return list;
  }

All of my data list is in countryDetails variable.

And the list is like this:

  [
    {
          "country_name": "Andorra",
          "alpha2_code": "AD",
          "states": [
            {"state_name": "Andorra la Vella"},
            {"state_name": "Canillo"},
          ]
    },
    ..............
    ..............
  ]

So, whats the problem here?

Answer 1

In the error it says you have two or more DropdownMenuItem with the same value , which is not allowed.

When I take a look at your code, it seems like you are passing c.countryName as the value, but could you double check and make sure that all of your country_name are unique?