您可以使用“DateTime”类中的“isBefore”和“isAfter”检查之前/之后。

DateTime startDate = DateTime.parse(service_start_date);
  DateTime endDate = DateTime.parse(service_end_date);
  
  DateTime now = DateTime.now();
  
  print('now: $now');
  print('startDate: $startDate');
  print('endDate: $endDate');
  print(startDate.isBefore(now));
  print(endDate.isAfter(now));

我做了一系列的扩展

extension DateTimeExtension on DateTime? {
  
  bool? isAfterOrEqualTo(DateTime dateTime) {
    final date = this;
    if (date != null) {
      final isAtSameMomentAs = dateTime.isAtSameMomentAs(date);
      return isAtSameMomentAs | date.isAfter(dateTime);
    }
    return null;
  }

  bool? isBeforeOrEqualTo(DateTime dateTime) {
    final date = this;
    if (date != null) {
      final isAtSameMomentAs = dateTime.isAtSameMomentAs(date);
      return isAtSameMomentAs | date.isBefore(dateTime);
    }
    return null;
  }

  bool? isBetween(
    DateTime fromDateTime,
    DateTime toDateTime,
  ) {
    final date = this;
    if (date != null) {
      final isAfter = date.isAfterOrEqualTo(fromDateTime) ?? false;
      final isBefore = date.isBeforeOrEqualTo(toDateTime) ?? false;
      return isAfter && isBefore;
    }
    return null;
  }

}

我希望它们是自我解释的，但显然你可以这样称呼它们
DateTime.now（）.isBefore（yourDate）
DateTime.now（）.isAfter（yourDate）
DateTime.now（）.isBetween（fromDate，toDate）

不要忘记检查这一天是否与两个日期中的一个相同，也可以在条件ex中添加一个或：if（start is before now||（start.month==now.month &&start.day==now.day ...etc）

由于@KuKu的答案基本上是正确的，但将设置为排他性的边界，我想提出一个抛光版本的@martinseal1987的答案。

extension DateTimeExtension on DateTime {
  bool isAfterOrEqual(DateTime other) {
    return isAtSameMomentAs(other) || isAfter(other);
  }

  bool isBeforeOrEqual(DateTime other) {
    return isAtSameMomentAs(other) || isBefore(other);
  }
  
  bool isBetween({required DateTime from, required DateTime to}) {
    return isAfterOrEqual(from) && isBeforeOrEqual(to);
  }
  
  bool isBetweenExclusive({required DateTime from, required DateTime to}) {
    return isAfter(from) && isBefore(to);
  }
}

// Test cases
void main() {
  final now = DateTime.now();
  final after = now.add(Duration(days: 1));
  final before = now.subtract(Duration(days: 1));
  
  print(now.isAfterOrEqual(now)); // true
  print(now.isBeforeOrEqual(now)); // true
  
  print(now.isAfterOrEqual(before)); // true
  print(now.isAfterOrEqual(after)); // false
  
  print(now.isBeforeOrEqual(after)); // true
  print(now.isBeforeOrEqual(before)); // false
  
  print(now.isBetween(from: before, to: after)); // true
  print(now.isBetween(from: now, to: now)); // true
  print(now.isBetween(from: before, to: now)); // true
  print(now.isBetween(from: now, to: after)); // true
  
  print(now.isBetweenExclusive(from: before, to: now)); // false
  print(now.isBetweenExclusive(from: now, to: after)); // false
}