可迭代的第一个坏状态：没有元素

Question

我正在尝试获取 driverfleet 数据以进行审查，但我收到以下错误

E/flutter (21563): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: Bad state: No element
E/flutter (21563): #0      Iterable.first (dart:core/iterable.dart:524:7)
E/flutter (21563): #1      _ReviewTransportsalesState.driverFleet (package:project_inovation/ui/screen/ReviewTransportsales.dart:504:10)
E/flutter (21563): <asynchronous suspension>
E/flutter (21563): #2      _ReviewTransportsalesState.initState (package:project_inovation/ui/screen/ReviewTransportsales.dart:171:5)
E/flutter (21563): #3      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4684:58)
E/flutter (21563): #4      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4520:5)
E/flutter (21563): #5      Element.inflateWidget (package:flutter/src/widgets/framework.dart:3490:14)
E/flutter (21563): #6      Element.updateChild (package:flutter/src/widgets/framework.dart:3258:18)

这是flutter显示的错误码

driverFleet(String value) async {
FleetModel fleetModel = FleetModel(value);
API _api = API();

Response response = await _api.fleetAPI(fleetModel);
xml.XmlDocument parsedFleet = xml.parse(response.data);
String fleetName = parsedFleet
    .findAllElements('DataRow')
    .first
    .findAllElements('field')
    .elementAt(0)
    .getAttribute('lval');
String fleetID = parsedFleet
    .findAllElements('DataRow')
    .first
    .findAllElements('field')
    .elementAt(1)
    .getAttribute('lval');
String productID = parsedFleet
    .findAllElements('DataRow')
    .first
    .findAllElements('field')
    .elementAt(3)
    .getAttribute('lval');

DriverModel driverModel = DriverModel(fleetID);

try {
  var driverResponse = await _api.driverAPI(driverModel);
  xml.XmlDocument parsedDriver = xml.parse(driverResponse.data);

  String driverID = parsedDriver
      .findAllElements('DataRow')
      .first
      .findAllElements('field')
      .elementAt(0)
      .getAttribute('lval');
  String driverName = parsedDriver
      .findAllElements('DataRow')
      .first
      .findAllElements('field')
      .elementAt(1)
      .getAttribute('lval');

  _fleetController.text = fleetName ?? 'B 9778 PYU';
  _driverController.text = driverName;
  _mySelectionDriver = driverID + driverName;
  _mySelectionProduct = productID;
  _fleetID = fleetID ?? '1000773';
  _driverID = driverID;
} catch (_) {
  _fleetController.text = fleetName ?? 'B 9778 PYU';
  _driverController.text = 'Aang T6';
  _mySelectionDriver = '1001465Aang T6';
  _mySelectionProduct = productID;
  _fleetID = fleetID ?? '1000773';
  _driverID = '1001427';
}

await readTransportSales(widget.recordID);
await readTransRoute(widget.recordID);
setState(() {});
}

我假设这会读取一个空列表，基于我在这里阅读的类似问题，我尝试使用他们的解决方案但仍然没有好处。

Answer 1

getters like first, last on Iterables 不安全使用并在空 Iterables 上调用时抛出 state 错误。

在您的代码中，您在 try catch 中有第二部分，

但是您的parsedFleet.findAllElements('DataRow') 有可能返回一个空的Iterable。

将此代码也移动到 try catch 中，或在访问 .findAllElements('field') 之前执行检查。