【发布时间】：2020-11-23 13:14:38
【问题描述】：
我是 Flutter 的新手，我正在尝试制作一个 Dropdownbuttom 项目，用户可以在其中从列表中选择一个项目（我从 FirebaseFirestore 获取），如果用户获取该项目，并使用按钮，其他用户将无法使用该项目。
这是我保存按钮中onPress() 函数的方法。
Future saveData(String uid, String enrollment) async {
// Limpiar la matricula donde aparezca el usuario.
final querySnapshot =
await FirebaseFirestore.instance.collection('Matriculas').get();
final enrollmentOld = querySnapshot.docs.firstWhere(
(doc) => doc['infoCoche']['idUser'] == uid,
orElse: () => null,
);
if (enrollmentOld != null) {
try {
FirebaseFirestore.instance
.collection('Matriculas')
.doc(enrollmentOld.id)
.update({
'infoCoche': {'idUser': uid, 'enUso': false}
});
} catch (e) {
print(e.toString());
}
}
//Update en la nueva matricula con el nuevo usuario
try {
FirebaseFirestore.instance
.collection('Matriculas')
.doc(enrollment)
.update({
'infoCoche': {'idUser': uid, 'enUso': true}
});
} catch (e) {
print(e.toString());
}
}
首先我搜索用户是否已经选择了一个注册，所以如果他想更改为另一个，我可以释放旧的。如果是这样，我将布尔 enUso 设置为 false。对他选择但真实的项目执行相同的操作。如果不这样做，我只是忽略该部分并将新注册的属性更改为 true。
这是DropDownButton。
var _currentItemSelected;
Widget _formSelectEnrollment() {
return StreamBuilder(
stream: FirebaseFirestore.instance.collection('Matriculas').snapshots(),
builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (!snapshot.hasData) {
return Center(
child: CircularProgressIndicator(),
);
}
List<DocumentSnapshot> docs = snapshot.data.docs;
List<String> listEnrollment = List();
for (DocumentSnapshot ids in docs) {
if (!ids['infoCoche']['enUso']) {
listEnrollment.add(ids.id);
}
}
return Container(
margin: EdgeInsets.symmetric(vertical: 10),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
'Seleccionar matricula',
style: TextStyle(fontWeight: FontWeight.bold, fontSize: 15),
),
SizedBox(
height: 10,
),
DropdownButtonFormField<String>(
items: listEnrollment.map((String dropDownStringItem) {
return DropdownMenuItem<String>(
value: dropDownStringItem,
child: Text(dropDownStringItem),
);
}).toList(),
validator: (value) => value == null
? 'Es necesario seleccionar una matricula'
: null,
onChanged: (String newValueSelected) {
setState(() {
_currentItemSelected = newValueSelected;
});
},
decoration: InputDecoration(
border: InputBorder.none,
fillColor: Color(0xfff3f3f4),
filled: true),
)
],
),
);
},
);
}
如您所见，我使用的是StreamBuilder()，因此我得到了一个列表，其中包含所有未使用的注册。另外由于它是一个流构建器，如果我在 FireStore 中更改某些内容，它会实时更改。
但是，出于某种我并不关心的原因，每次我尝试选择一个新的注册并保存它时，它都会返回下一个错误。
Performing hot reload...
Reloaded 4 of 838 libraries in 282ms.
I/flutter (17066): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (17066): The following assertion was thrown building Builder(dirty, dependencies: [_FocusMarker]):
I/flutter (17066): There should be exactly one item with [DropdownButton]'s value: 5816KNK.
I/flutter (17066): Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
I/flutter (17066): 'package:flutter/src/material/dropdown.dart':
I/flutter (17066): Failed assertion: line 834 pos 15: 'items == null || items.isEmpty || value == null ||
I/flutter (17066): items.where((DropdownMenuItem<T> item) {
I/flutter (17066): return item.value == value;
I/flutter (17066): }).length == 1'
I/flutter (17066):
I/flutter (17066): Either the assertion indicates an error in the framework itself, or we should provide substantially
I/flutter (17066): more information in this error message to help you determine and fix the underlying cause.
I/flutter (17066): In either case, please report this assertion by filing a bug on GitHub:
I/flutter (17066): https://github.com/flutter/flutter/issues/new?template=BUG.md
I/flutter (17066):
I/flutter (17066): The relevant error-causing widget was:
I/flutter (17066): DropdownButtonFormField<String>
I/flutter (17066): file:///C:/Users/Sharki/Documents/4.%20Proyecto%20flutter/Pruebas%20Flutter/Asereje/lib/paginas/accountSettings.dart:55:15
I/flutter (17066):
I/flutter (17066): When the exception was thrown, this was the stack:
I/flutter (17066): #2 new DropdownButton (package:flutter/src/material/dropdown.dart:834:15)
I/flutter (17066): #3 new DropdownButtonFormField.<anonymous closure>.<anonymous closure> (package:flutter/src/material/dropdown.dart:1525:27)
I/flutter (17066): #4 Builder.build (package:flutter/src/widgets/basic.dart:7183:48)
I/flutter (17066): #5 StatelessElement.build (package:flutter/src/widgets/framework.dart:4701:28)
I/flutter (17066): #6 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)
I/flutter (17066): #7 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #8 StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
I/flutter (17066): #9 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #10 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
I/flutter (17066): #11 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #12 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
I/flutter (17066): #13 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #14 ProxyElement.update (package:flutter/src/widgets/framework.dart:4987:5)
I/flutter (17066): #15 _InheritedNotifierElement.update (package:flutter/src/widgets/inherited_notifier.dart:183:11)
I/flutter (17066): #16 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #17 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
I/flutter (17066): #18 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
I/flutter (17066): #19 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #20 StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
I/flutter (17066): #21 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #22 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
I/flutter (17066): #23 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
I/flutter (17066): #24 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #25 StatefulElement.update (package:flutter/src/widgets/framework.dart:4832:5)
I/flutter (17066): #26 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #27 RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:5647:32)
I/flutter (17066): #28 MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6246:17)
I/flutter (17066): #29 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #30 SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:6125:14)
I/flutter (17066): #31 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #32 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
I/flutter (17066): #33 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #34 StatelessElement.update (package:flutter/src/widgets/framework.dart:4708:5)
I/flutter (17066): #35 Element.updateChild (package:flutter/src/widgets/framework.dart:3314:15)
I/flutter (17066): #36 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
I/flutter (17066): #37 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
I/flutter (17066): #38 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
I/flutter (17066): #39 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2730:33)
I/flutter (17066): #40 WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:913:20)
I/flutter (17066): #41 RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:302:5)
I/flutter (17066): #42 SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1117:15)
I/flutter (17066): #43 SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1055:9)
I/flutter (17066): #44 SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:971:5)
I/flutter (17066): #48 _invoke (dart:ui/hooks.dart:251:10)
I/flutter (17066): #49 _drawFrame (dart:ui/hooks.dart:209:3)
I/flutter (17066): (elided 5 frames from class _AssertionError and dart:async)
I/flutter (17066):
I/flutter (17066): ════════════════════════════════════════════════════════════════════════════════════════════════════
正如我所说，我真的是 Flutter 的新手，也对不起我的英语。
【问题讨论】：