check list if it is empty or null flutter-CodePudding

I get this from the server, and I need to put my checkbox to true for values with null, while I don't have to do anything if I find []

{"FRI": [null], "MON": [null], "SAT": [null], "SUN": [{"to": "16:27", "from": "15:27"}], "THU": [null], "TUE": [null], "WED": []}

I'm trying with a

if (widget.initialValues!.every((e) => e == null)) {
  _isClosed.trigger(true);
}

but it does not work correctly because in both cases it returns to be true

CodePudding user response：

when you try to use each item of an array and compare it to null, [null] and [] would have similar results. Instead, you should use .isEmpty because this method defines that is an array is empty or not, and in this approach [null] and []` are not equal because the first one has one element but the other one has 0 elements! For example:

//an example list
const list = [ [], [null]];
  
  for(int i=0; i<list.length; i  ){
    if(list[i].isEmpty){
      print("empty "   i.toString());
    } else {
      print("not empty "   i.toString());
    }
  }

and the result will be:

empty 0
not empty 1

Similarly, you can use .length as follow:

const list = [ [], [null]];
for(int i=0; i<list.length; i  ){
    print(i.toString()   " length is "   list[i].length.toString());
  }

These are only examples and you can map them to your code as well.

CodePudding user response：

sorry if I reply to you with another account but I am at home with another pc and I do not have a user, I hope you will read ..

      final List<OpeningHours?>? initialValues;

class OpeningHours {
  OpeningHours({
    required this.open,
    required this.close,
  }) : assert(
          open.isBefore(close),
          "L'apertura dev'essere per forza prima della chiusura",
        );

  factory OpeningHours.fromMap(Map map) {
    if (!map.containsKey('from') || !map.containsKey('to')) {
      final msg =
          'La mappa $map non è valida per creare un oggetto [OpeningTime]';
      throw Exception(msg);
    }
    final from = TimeOfDayExtension.parse(map['from']! as String);
    final to = TimeOfDayExtension.parse(map['to']! as String);
    return OpeningHours(open: from, close: to);
  }

  final TimeOfDay open;

  final TimeOfDay close;

  String get format => '${open.asString()}-${close.asString()}';

  @override
  String toString() => jsonEncode(toMap());

  Map<String, String> toMap() =>
      {'from': open.asString(), 'to': close.asString()};
}