Warning: Operand of null-aware operation '??' has type 'int' which excludes null. _countries.indexWhere((country)

onTap: () {
    int index =
        _countries.indexWhere((country) {
              return country.startsWith(
                  alphabet.toUpperCase());
            }) ??
            0;
    _listController.jumpTo(
      index * 60.0,
    );
  },
  child: Text(
    alphabet,
    style: TextStyle(
      color: _theme.primaryColor,
      fontSize: 14.0,
      fontWeight: FontWeight.bold,
    ),
  ),

CodePudding user response：

According to documentation, List.indexWhere always returns int - if the element isn't found, the return value is -1, but you seem to be thinking that it's null.

CodePudding user response：

The documentation on indexWhere clearly states:

Returns -1 if element is not found.

So there is no possible way that your call returns null. The ?? operator only works on a nullable variable/expression, because it will return the result, or (in your case) 0 if the result is null. The result can never be null so your compiler tells you that that statement does not make any sense.

If you wanted the -1 to also be 0, you could use min to make sure the minimum you get is always 0.

CodePudding user response：

indexWhere doesn't return nullable int. You might want firstWhere and then find index.

String item = _countries.firstWhere((country) {
    return country.startsWith(alphabet.toUpperCase());
  }, orElse: () => _countries.first);

  int index = _countries.indexWhere((element) => element == item);

int selectedIndex = 0;
for (int i = 0; i < _countries.length; i  ) {
  if (_countries[i].startsWith(alphabet.toUpperCase())) {
    selectedIndex = i;
    break;
  }
}

I hope there are better ways of doing it.