如何为波动年份添加范围验证

Question

我尝试添加年份范围验证，它必须在1850年到当前年份之间。我已经尝试过了，但是没有用。

这是我尝试过的代码

  String validateestablishedyear(String value) {
    var date = new DateTime.now();
    int currentYear = date.year;
    int userinputValue = 0;
    print('currentYear = $currentYear');
    print('input value = $value');
    print('value = ${value is int}');
    print('value = ${value is String}');

    if (value is String && value.length == 0) {
      return "Established Year is Required";
    } else {
      userinputValue = int.parse(value);
    }

    if (userinputValue < 1850 && userinputValue >= currentYear) {
      return "Year must be between 1850 and $currentYear";
    }
    return null;
  }

Answer 1

只需如下更改您的代码，

if (userinputValue < 1850 || userinputValue >= currentYear) {
  return "Year must be between 1850 and $currentYear";
}

您的逻辑是错误的。您应该使用||代替&&