flutter - 错误状态 : No element

Question

我只是想知道那是为了什么？什么时候来，是不是API问题？

         BlocBuilder<OrderBloc, OrderState>(
                  builder: (context, finalstate) {
                    if (state is OrderLoaded) {
                      for (var item in state.orderSent) {
                        totalweightsforsent.add(item.totalWeight);
//right here when i fetch the data from API and when it is done it is not going forward anymore
                      }
                      for (var item in state.orderPackaging) {
                        totalforpacking.add(item.totalWeight);
                      }

Answer 1

不，它不是一个API问题，它出于某种原因

让我们看一下首先的示例从列表中获取颜色字符串

无效颜色字符串

void main() {
  List<String> list = ['red', 'yellow', 'pink', 'blue'];
  var newList = list.firstWhere((element) => element.contains('green'), 
      orElse: () => 'No matching color found');
  print(newList);
}

输出:

没有找到匹配的颜色

有效颜色字符串

 void main() {
      List<String> list = ['red', 'yellow', 'pink', 'blue'];
      var newList = list.firstWhere((element) => element.contains('blue'), 
          orElse: () => 'No matching color found');
      print(newList);
    }

输出:

蓝色

上面，所有都是有效的情况

void main() {
  List<String> list = ['red', 'yellow', 'pink', 'blue'];
  var newList = list.firstWhere((element) => element.contains('green'));
  print(newList);
}

输出:

[verbose-2:ui_dart_state.cc(171)]未经治疗的异常(exception):不良状态:无元素