使用 FutureBuilder 和 Provider 在 Flutter 中没有元素的错误状态

Question

使用Provider和FutureBuilder，我刚刚从数据库中删除了数据，同时它也被删除了，它显示一个红色的屏幕，状态不好，没有元素。添加数据没有问题，不显示这个问题。代码如下

堆栈跟踪

ter (12519): ??? EXCEPTION CAUGHT BY WIDGETS LIBRARY ????????????????????????????????????????????????????????????
I/flutter (12519): The following StateError was thrown building ViewNoteScreen(dirty, dependencies:
I/flutter (12519): [_ModalScopeStatus], state: _ViewNoteScreenState#f589b):
I/flutter (12519): Bad state: No element
I/flutter (12519): 
I/flutter (12519): The relevant error-causing widget was:
I/flutter (12519):   ViewNoteScreen file:///C:/Users/Admin/Desktop/daily%2010/provider_note/lib/main.dart:21:46
I/flutter (12519):
I/flutter (12519): When the exception was thrown, this was the stack:
I/flutter (12519): #0      ListMixin.firstWhere (dart:collection/list.dart:148:5)
I/flutter (12519): #1      Providers.findById (package:provider_note/helper/provider.dart:14:19)
I/flutter (12519): #2      _ViewNoteScreenState.build (package:provider_note/screens/view_note.dart:21:35)
I/flutter (12519): #3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4663:28)
I/flutter (12519): #4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4546:15)
I/flutter (12519): #5      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4719:11)
I/flutter (12519): #6      Element.rebuild (package:flutter/src/widgets/framework.dart:4262:5)
I/flutter (12519): #7      BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2667:33)
I/flutter (12519): #8      WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:866:20)
I/flutter (12519): #9      RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:286:5)
I/flutter (12519): #10     SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1117:15)
I/flutter (12519): #11     SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1056:9)
I/flutter (12519): #12     SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:972:5)
I/flutter (12519): #16     _invoke (dart:ui/hooks.dart:253:10)
I/flutter (12519): #17     _drawFrame (dart:ui/hooks.dart:211:3)
I/flutter (12519): (elided 3 frames from dart:async)
I/flutter (12519):
I/flutter (12519): ??????????????????????????????????????????????

Answer 1

BadStateException 当列表不包含该项目并且仍然有人在搜索该项目时发生

例子：

如果orElse代码中没有定义并且错误的项目得到了列表中不存在的搜索，那么它会显示BadStateException

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

输出：

Uncaught Error: Bad state: No element

解决方案：添加 orElse

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

输出：

No matching color found