DropdownButtonFormField gives Error when try to display String

Question

I want to make DropdownButtonFormField that shows cities like this:

final List<String> cities = ['London', 'New York', 'Paris', 'Shanghahai', 'Tokyo'];

String _currentCity;

DropdownButtonFormField(
            value: _currentCity ?? ' ',
            decoration: textInputDecoration,
            items: cities.map((city) {
              return DropdownMenuItem(
                value: city,
                child: Text('$city City '),
              );
            }).toList(),
            onChanged: (val) => setState(() => _currentCity = val ),
          ),

But when I try to show these Strings I get red screen error :

and If I changed the Strings inside the List to numbers it works well:

 final List<String> cities = ['0', '1', '2', '3', '4'];

Can someone tell me what is wrong with it although I use List of strings

dangngocduc · Accepted Answer · 2020-06-01 15:43:12Z

1

You can try set _currentCity for default value?

String _currentCity = 'London';

answered Jun 1, 2020 at 15:43

dangngocduc

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