颤振中出现"Tried to paint a RenderObject reentrantly."错误？

Question

我试图从API获取国家名称，并将其显示在下拉框中。我正在使用集团图书馆进行国家管理。

这是我的密码。

select_input_field.dart-DropdownButtonField 的自定义包装程序

import 'package:flutter/material.dart';
class SelectInputField extends StatelessWidget {
final String label;
final List<String> options;
final TextEditingController controller;
final EdgeInsets padding;
const SelectInputField(this.label, this.options,
{ Key? key,
required this.controller,
this.padding =
const EdgeInsets.only(top: 8, bottom: 8, left: 30, right: 30)})
: super(key: key);
@override
Widget build(BuildContext context) {
return Padding(
padding: padding,
child: DropdownButtonFormField(
decoration: InputDecoration(
labelText: label,
labelStyle: Theme.of(context).textTheme.bodyMedium,
border: OutlineInputBorder(
borderSide: BorderSide(
color: Theme.of(context).primaryColorDark,
width: 1,
),
),
enabledBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Theme.of(context).primaryColorDark,
width: 1,
),
),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Theme.of(context).colorScheme.secondary,
width: 1,
),
),
fillColor: Theme.of(context).primaryColorLight),
style: Theme.of(context).textTheme.bodyMedium,
items: options.map((String value) {
print(value);
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
onChanged: (String? value) {
controller.text = value ?? '';
},
),
);
}
}

这就是我用来构建它的方法

Widget _countriesDropDown(BuildContext context, TextEditingController controller){
return BlocProvider(
create: (context) => _signupBloc,
child: BlocBuilder<SignupBloc,SignupState>(
buildWhen: ((previous, current) => previous is! Loaded && current is Loaded),
builder: (context, state){
if (state is Initial){
_signupBloc.add(LoadEvent());
}
else if (state is Loaded){
countries = state.countries;
return SelectInputField("Country", countries, controller: controller);
}
return CircularProgressIndicator(color: Theme.of(context).colorScheme.secondary,);
},
)
);
}

我的集体课如下。

class SignupBloc extends Bloc<SignupEvent, SignupState> {
static const String countriesUrl = "https://api.first.org/data/v1/countries";
SignupBloc() : super(Initial()) {
on<LoadEvent>((event, emit) async{
emit(Loading());
List<String> countries = [];
try{
final response = await http.get(Uri.parse(countriesUrl));
if(response.statusCode == 200){
var responseJson = jsonDecode(response.body);
responseJson['data'].values.forEach((element) {
countries.add(element['country']);
});
emit(Loaded(countries));
}
else{
emit(Failed("Error in getting data"));
}
}
catch(e){
print(e);
emit(Failed("Failed to access internet. Try again later!"));
}
});
}

错误看起来像这样。我不明白这个错误发生在哪里

======== Exception caught by rendering library =====================================================
The following assertion was thrown during paint():
Tried to paint a RenderObject reentrantly.
The following RenderObject was already being painted when it was painted again: RenderPointerListener#c100e relayoutBoundary=up20 NEEDS-PAINT
...  needs compositing
...  parentData: <none> (can use size)
...  constraints: BoxConstraints(0.0<=w<=351.4, 0.0<=h<=Infinity)
...  size: Size(351.4, 64.0)
...  behavior: opaque
...  listeners: down, panZoomStart
Since this typically indicates an infinite recursion, it is disallowed.
The relevant error-causing widget was: 
DropdownButtonFormField<String> DropdownButtonFormField:file:///D:/Projects/sem5/iblock/lib/widgets/forms/select_input_field.dart:20:14
When the exception was thrown, this was the stack: 
#0      RenderObject._paintWithContext.<anonymous closure> (package:flutter/src/rendering/object.dart:2693:9)
#1      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2706:6)
#2      PaintingContext.paintChild (package:flutter/src/rendering/object.dart:239:13)
#3      RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:144:15)
#4      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2796:7)
#5      PaintingContext.paintChild (package:flutter/src/rendering/object.dart:239:13)
#6      RenderProxyBoxMixin.paint (package:flutter/src/rendering/proxy_box.dart:144:15)
#7      RenderObject._paintWithContext (package:flutter/src/rendering/object.dart:2796:7)

我需要一个关于我的代码出了什么问题以及如何修复的解释。

flutter doctor输出

[√] Flutter (Channel stable, 3.3.2, on Microsoft Windows [Version 10.0.22621.608], locale en-US)
• Flutter version 3.3.2 on channel stable at C:flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision e3c29ec00c (3 weeks ago), 2022-09-14 08:46:55 -0500
• Engine revision a4ff2c53d8
• Dart version 2.18.1
• DevTools version 2.15.0
[√] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
• Android SDK at C:UsersISHADAppDataLocalAndroidsdk
• Platform android-32, build-tools 30.0.3
• Java binary at: C:Program FilesAndroidAndroid Studiojrebinjava
• Java version OpenJDK Runtime Environment (build 11.0.13+0-b1751.21-8125866)
• All Android licenses accepted.
[√] Chrome - develop for the web
• CHROME_EXECUTABLE = C:Program FilesBraveSoftwareBrave-BrowserApplicationbrave.exe
[√] Visual Studio - develop for Windows (Visual Studio Build Tools 2019 16.11.18)
• Visual Studio at C:Program Files (x86)Microsoft Visual Studio2019BuildTools
• Visual Studio Build Tools 2019 version 16.11.32802.440
• Windows 10 SDK version 10.0.19041.0
[√] Android Studio (version 2021.3)
• Android Studio at C:Program FilesAndroidAndroid Studio
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 11.0.13+0-b1751.21-8125866)
[√] IntelliJ IDEA Ultimate Edition (version 2022.2)
• IntelliJ at C:Program FilesJetBrainsIntelliJ IDEA 2022.1.2
• Flutter plugin version 70.2.5
• Dart plugin version 222.4167.21
[√] VS Code (version 1.71.2)
• VS Code at C:UsersISHADAppDataLocalProgramsMicrosoft VS Code
• Flutter extension version 3.48.0
[√] Connected device (3 available)
• Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version 10.0.22621.608]
• Chrome (web)      • chrome  • web-javascript • unknown
• Edge (web)        • edge    • web-javascript • Microsoft Edge 105.0.1343.53
! Device DRGGAM5890805202 is not authorized.
You might need to check your device for an authorization dialog.
[√] HTTP Host Availability
• All required HTTP hosts are available
• No issues found!

PS：我对Flutter/block库不太熟悉。

Answer 1

不确定您是否仍然存在此问题，但我遇到了类似的问题，我将isExpanded: true添加到我的DropdownButtonFormField中，从而解决了错误。我的问题是由DropdownMenuItem中的单词长度引起的。当我查看您的API调用的响应时，我看到了一些非常长的名称。我可能错了，虽然

Answer 2

将SelectInputField转换为StatefulWidget解决了这个问题。我认为DropdownButtonFormField需要根据它上面的活动来呈现它自己。因此，StatelessWidget不能重新呈现它自己，从而导致这个问题。

Answer 3

我遇到了同样的问题，我能够解决它。

问题出在DropdownButtonFormField上。它应该具有"value"属性。