我有一个没有数据的FutureBuilder。我有这个函数从后端获取数据：

Future<List<OrderReceipt>> getOrderReceipt(orderno) async {
  final response = await HttpService.order_receipt(orderno);
  var decoded = json.decode(response.body)["qry"].cast<Map<String,dynamic>>();
  print(decoded);
  var OrderR = await decoded.map<OrderReceipt>((json) => OrderReceipt.fromJson(json)).toList();
  return OrderR;
}

这是具有Map函数的类：

class OrderReceipt {
  final String LUKEBLART;
  final String LUKEBLOART;
  final String LUKEBLONR;
  final String LUKEBLVC;
  final String LUKEBLBNR;
  final String LUKEBLDRAKT;
  final String LUKEBLADS;
  final String LUKEBLDATUM;
  final String LUKEBLPGM;
  final String LUKETIME;
  final String LUKESART;
  final String LUKEPAGE;
  final String LUKELINE;
  final String LUKELNR;
  final String LUKETXT;

  OrderReceipt({
    required this.LUKEBLART,
    required this.LUKEBLOART,
    required this.LUKEBLONR,
    required this.LUKEBLVC,
    required this.LUKEBLBNR,
    required this.LUKEBLDRAKT,
    required this.LUKEBLADS,
    required this.LUKEBLDATUM,
    required this.LUKEBLPGM,
    required this.LUKETIME,
    required this.LUKESART,
    required this.LUKEPAGE,
    required this.LUKELINE,
    required this.LUKELNR,
    required this.LUKETXT,
  });

  factory OrderReceipt.fromJson(Map<String, dynamic> json) {
    return OrderReceipt(
        LUKEBLART: json['LUKEBLART'] as String ?? '', 
        LUKEBLOART: json['LUKEBLOART'] as String ?? '',   
        LUKEBLONR: json['LUKEBLONR'] as String ?? '',  
        LUKEBLVC: json['LUKEBLVC'] as String ?? '', 
        LUKEBLBNR: json['LUKEBLBNR'] as String ?? '', 
        LUKEBLDRAKT: json['LUKEBLDRAKT'] as String ?? '', 
        LUKEBLADS: json['LUKEBLADS'] as String ?? '', 
        LUKEBLDATUM: json['LUKEBLDATUM'] as String ?? '',  
        LUKEBLPGM: json['LUKEBLPGM'] as String ?? '',
        LUKETIME: json['LUKETIME'] as String ?? '',
        LUKESART: json['LUKESART'] as String ?? '', 
        LUKEPAGE: json['LUKEPAGE'] as String ?? '', 
        LUKELINE: json['LUKELINE'] as String ?? '', 
        LUKELNR: json['LUKELNR'] as String ?? '', 
        LUKETXT: json['LUKETX'] as String ?? '', 
    );}
}

下面是json的一个例子（只有一个数据集）：

[{LUKEBLADS: 222222, LUKEBLART: W , LUKEBLBNR: 333333, LUKEBLDATUM: 20230113, LUKEBLDRAKT: FX  , LUKEBLOART: FX  , LUKEBLONR: 4444, LUKEBLPGM: XXXKG    , LUKEBLVC: X1 , LUKELINE: 41, LUKELNR: 36, LUKEPAGE: 1, LUKESART: 1, LUKETIME: Fri, 13 Jan 2023 09:54:02 GMT, LUKETXT:                                    ExampleText                                      USD         66,20                                                                                          },]

LUKETXT中有很多空格，因为我正在用等宽字体生成一个.pdf（只是为了从我正在使用的AS 400数据库中获得良好的大小调整）
问题出在getOrderReceipt(orderno) Future中，Future打印decoded，但未从await decoded.map<OrderReceipt>((json) => OrderReceipt.fromJson(json)).toList();返回任何内容。
我没有收到任何错误-构建Future<List<OrderReceipt>>的FutureBuilder处理了大约两秒钟，然后就没有数据了。我的项目中还有另外两个FutureBuilder，它们没有任何问题。有人知道错误吗？
谢谢

编辑1：

@约佐特，@埃里克·马丁和@帕玛蒂亚斯：我已经更新了FutureFunction并删除了.cast<Map<String,dynamic>>()和await，但执行中没有任何变化-错误仍然存在，函数以不从decoded.map<OrderReceipt>((json) => OrderReceipt.fromJson(json)).toList();返回任何内容结束-我更新的函数：

Future<List<OrderReceipt>> getOrderReceipt(orderno) async {
  final response = await HttpService.order_receipt(orderno);
  print(response);
  var decoded = json.decode(response.body)["qry"];
  var OrderR = decoded.map<OrderReceipt>((json) => OrderReceipt.fromJson(json)).toList();
  print(OrderReceipt);
  return OrderR;
}

我还尝试将工厂函数更改为：

...
...
  factory OrderReceipt.fromJson(json) {
    return OrderReceipt(
          ...
          ...
      ); }
...
...

**EDIT 2：**这是在带有try-catch-Block的FutureFunction的注解中讨论的：

Future<List<OrderReceipt>> getOrderReceipt(orderno) async {
  try {
    final response = await HttpService.order_receipt(orderno);
    print(response);
    var decoded = json.decode(response.body)["qry"];
    var OrderR = decoded.map<OrderReceipt>((json) =>
        OrderReceipt.fromJson(json)).toList();
    return OrderR;
  } catch(err) {
    print('Caught error: $err');
    throw 'Caught error: $err';
  }
}

显示以下错误：

type 'null' is not a subtype of type 'string' in type cast

我还尝试注解掉Modell中的“LUKETXT”--然后它就工作了。也许这个错误会被抛出，因为值中可能有点，冒号和其他特殊字符？-〉但正如我在devtools中看到的，这些特殊字符在json.decode函数中被正确解码到每个头部，并保持为字符串。