小贝子编程

在单击DropdownButtonFormField时引发错误



我正在尝试在颤振网络上的选项卡控制器中使用带有选项卡查看器的DropdownButtonFormField。它显示但不显示下拉选项，单击它显示错误，请在下面找到我的代码和错误。

下面是我的示例代码：

import 'package:flutter/material.dart';
class UserManager extends StatefulWidget {
const UserManager({Key? key}) : super(key: key);
@override
_UserManagerState createState() => _UserManagerState();
}
class _UserManagerState extends State<UserManager> {
final _formkey = GlobalKey<FormState>();
var addName = "";
var addEmail = "";
var addPassword = "";
var addRole = "";

final nameController = TextEditingController();
final emailController = TextEditingController();
final passwordController = TextEditingController();
final roleController = TextEditingController();
@override
Widget build(BuildContext context) {
return MaterialApp(
home: DefaultTabController(
length: 2,
child: Scaffold(
appBar: AppBar(
toolbarHeight: 20,
bottom: const TabBar(
tabs: [
Tab(icon: Icon(Icons.person_add)),
Tab(icon: Icon(Icons.edit)),
],
),
),
body: TabBarView(
children: [
Center(
child: Form(
key: _formkey,
child: SingleChildScrollView(
reverse: true,
child: Container(
width: 420,
margin: const EdgeInsets.all(10.0),
padding: const EdgeInsets.all(16),
decoration: BoxDecoration(
border: Border.all(color: Colors.grey),
borderRadius: const BorderRadius.all(
Radius.circular(10),
),
),
child: Column(
children: [
//const SizedBox(
//height: 50,
//),
const Text(
"Add name",
style: TextStyle(
fontSize: 20,
fontWeight: FontWeight.bold,
color: Colors.indigo,
),
),
const SizedBox(
height: 10,
),
TextFormField(
minLines: 1,
autofocus: false,
keyboardType: TextInputType.text,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Name",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: nameController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Name';
}
return null;
}),
const SizedBox(
height: 10,
),
TextFormField(
autofocus: false,
minLines: 1,
keyboardType: TextInputType.emailAddress,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Email Address",
//hintText: "Email",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: emailController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Email ID';
} else if (!value.contains('@')) {
return 'Please Enter Valid Email ID';
}
return null;
}),
const SizedBox(
height: 10,
),
TextFormField(
minLines: 1,
autofocus: false,
obscureText: true,
keyboardType: TextInputType.text,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Password",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: passwordController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Password';
}
return null;
}),
const SizedBox(
height: 20,
),
//
DropdownButtonFormField(
decoration: const InputDecoration(
labelText: "department",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
hint: const Text("select department"),
value: addRole,
onChanged: (String? newValue) {
setState(() {
addRole = newValue!;
});
},
validator: (value) => value == null ? 'field required' : null,
items: <String>[
'',
'hr',
'dtp'
].map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
),
const SizedBox(
height: 20,
),
//
ElevatedButton(
style: ElevatedButton.styleFrom(
primary: Colors.red, // background
onPrimary: Colors.white, // foreground
),
onPressed: ()  {}
child: const Text('User Add'),
),
const SizedBox(
height: 20,
),
],
),
),
)),
),
Center(
child: Text("Test"),
)
],
),
),
),
);
}
}

下面是错误：

发生异常。"错误：无法命中测试具有以下特征的呈现框 从未布置过。对此调用了 hitTest() 方法。 渲染框：渲染语义注释#119e3 需求-布局需求-绘制： 需要合成创建者：语义← _EffectiveTickerMode ← TickerMode ← _OverlayEntryWidget-[LabeledGlobalKey<_OverlayEntryWidgetState>#c466c] ← _Theatre ← overlay-[LabeledGlobalKey#26f68] ← 非托管还原范围 ← _FocusMarker ← 语义 ← 焦点范围 ← 吸收指针←侦听器← ⋯ 父数据：未定位; 偏移量=偏移量(0.0， 0.0) 约束：缺少大小：缺少 不幸的是，这个物体的几何形状目前还不知道， 可能是因为它从未被布置过。这意味着它不可能 准确命中测试。如果尝试在 布局阶段本身，请确保仅命中具有以下功能的测试节点 完成的布局(例如，节点的子节点，在其布局()之后) 方法已调用)。

调试控制台：

════════ Exception caught by rendering library ═════════════════════════════════
The following assertion was thrown during performLayout():
LayoutBuilder does not support returning intrinsic dimensions.
Calculating the intrinsic dimensions would require running the layout callback speculatively, which might mutate the live render object tree.
The relevant error-causing widget was
SliverFillRemaining
When the exception was thrown, this was the stack
The following RenderObject was being processed when the exception was fired: RenderSliverFillRemaining#ef0f7 relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
RenderObject: RenderSliverFillRemaining#ef0f7 relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
needs compositing
parentData: paintOffset=Offset(0.0, 0.0) (can use size)
constraints: SliverConstraints(AxisDirection.down, GrowthDirection.forward, ScrollDirection.idle, scrollOffset: 0.0, remainingPaintExtent: 574.0, crossAxisExtent: 1034.0, crossAxisDirection: AxisDirection.right, viewportMainAxisExtent: 574.0, remainingCacheExtent: 824.0, cacheOrigin: 0.0)
geometry: SliverGeometry(scrollExtent: 574.0, paintExtent: 574.0, maxPaintExtent: 574.0, cacheExtent: 574.0)
scrollExtent: 574.0
paintExtent: 574.0
maxPaintExtent: 574.0
cacheExtent: 574.0
child: RenderFlex#0b053 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
needs compositing
parentData: paintOffset=Offset(0.0, -0.0)
constraints: BoxConstraints(w=1034.0, h=574.0)
size: Size(1034.0, 574.0)
direction: horizontal
mainAxisAlignment: start
mainAxisSize: max
crossAxisAlignment: center
textDirection: ltr
verticalDirection: down
child 1: RenderSemanticsAnnotations#79122 relayoutBoundary=up1
needs compositing
parentData: offset=Offset(0.0, 0.0); flex=null; fit=null (can use size)
constraints: BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=574.0)
size: Size(89.0, 574.0)
child: RenderPhysicalModel#2413b relayoutBoundary=up2
needs compositing
parentData: <none> (can use size)
constraints: BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=574.0)
layer: PhysicalModelLayer#dd0a6
engine layer: PhysicalShapeEngineLayer#2eafd
handles: 2
elevation: 0.0
color: Color(0xffffffff)
size: Size(89.0, 574.0)
elevation: 0.0
color: Color(0xffffffff)
shadowColor: Color(0xffffffff)
shape: BoxShape.rectangle
borderRadius: BorderRadius.zero
child: _RenderInkFeatures#f1226 relayoutBoundary=up3
parentData: <none> (can use size)
constraints: BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=574.0)
size: Size(89.0, 574.0)
child 2: RenderConstrainedBox#5423b relayoutBoundary=up1
parentData: offset=Offset(89.0, 0.0); flex=null; fit=null (can use size)
constraints: BoxConstraints(0.0<=w<=Infinity, 0.0<=h<=574.0)
size: Size(1.0, 574.0)
additionalConstraints: BoxConstraints(w=1.0, 0.0<=h<=Infinity)
child: RenderPositionedBox#2ef82 relayoutBoundary=up2
parentData: <none> (can use size)
constraints: BoxConstraints(w=1.0, 0.0<=h<=574.0)
size: Size(1.0, 574.0)
alignment: Alignment.center
textDirection: ltr
widthFactor: expand
heightFactor: expand
child: RenderPadding#25c65 relayoutBoundary=up3
parentData: offset=Offset(0.0, 0.0) (can use size)
constraints: BoxConstraints(0.0<=w<=1.0, 0.0<=h<=574.0)
size: Size(1.0, 574.0)
padding: EdgeInsets.zero
textDirection: ltr
child 3: RenderSemanticsAnnotations#7f0ab relayoutBoundary=up1 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
needs compositing
parentData: offset=Offset(90.0, 0.0); flex=1; fit=FlexFit.tight (can use size)
constraints: BoxConstraints(w=944.0, 0.0<=h<=574.0)
size: Size(944.0, 574.0)
child: RenderSemanticsAnnotations#466c4 relayoutBoundary=up2 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
needs compositing
parentData: <none> (can use size)
constraints: BoxConstraints(w=944.0, 0.0<=h<=574.0)
size: Size(944.0, 574.0)
child: RenderSemanticsAnnotations#4f301 relayoutBoundary=up3 NEEDS-LAYOUT NEEDS-COMPOSITING-BITS-UPDATE
needs compositing
parentData: <none> (can use size)
constraints: BoxConstraints(w=944.0, 0.0<=h<=574.0)
size: Size(944.0, 574.0)
════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by scheduler library ═════════════════════════════════
Cannot hit test a render box that has never been laid out.
════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by scheduler library ═════════════════════════════════
Assertion failed:
!_debugDuringDeviceUpdate
is not true

在州级别，类String? addRole;和从Items<String>[]中删除''。

在User Add

onPressed: () {
bool isValid =
_formkey.currentState!.validate();
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(
content: Text("form is $isValid")));
},
},

完整小部件


class _UserManagerState extends State<UserManager> {
final _formkey = GlobalKey<FormState>();
var addName = "";
var addEmail = "";
var addPassword = "";
String? addRole;
final nameController = TextEditingController();
final emailController = TextEditingController();
final passwordController = TextEditingController();
final roleController = TextEditingController();
@override
Widget build(BuildContext context) {
return MaterialApp(
home: DefaultTabController(
length: 2,
child: Scaffold(
appBar: AppBar(
toolbarHeight: 20,
bottom: const TabBar(
tabs: [
Tab(icon: Icon(Icons.person_add)),
Tab(icon: Icon(Icons.edit)),
],
),
),
body: TabBarView(
children: [
Center(
child: Form(
key: _formkey,
child: SingleChildScrollView(
reverse: true,
child: Container(
width: 420,
margin: const EdgeInsets.all(10.0),
padding: const EdgeInsets.all(16),
decoration: BoxDecoration(
border: Border.all(color: Colors.grey),
borderRadius: const BorderRadius.all(
Radius.circular(10),
),
),
child: Column(
children: [
//const SizedBox(
//height: 50,
//),
const Text(
"Add name",
style: TextStyle(
fontSize: 20,
fontWeight: FontWeight.bold,
color: Colors.indigo,
),
),
const SizedBox(
height: 10,
),
TextFormField(
minLines: 1,
autofocus: false,
keyboardType: TextInputType.text,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Name",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: nameController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Name';
}
return null;
}),
const SizedBox(
height: 10,
),
TextFormField(
autofocus: false,
minLines: 1,
keyboardType: TextInputType.emailAddress,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Email Address",
//hintText: "Email",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: emailController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Email ID';
} else if (!value.contains('@')) {
return 'Please Enter Valid Email ID';
}
return null;
}),
const SizedBox(
height: 10,
),
TextFormField(
minLines: 1,
autofocus: false,
obscureText: true,
keyboardType: TextInputType.text,
textInputAction: TextInputAction.next,
decoration: const InputDecoration(
labelText: "Password",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
controller: passwordController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Password';
}
return null;
}),
const SizedBox(
height: 20,
),
//
DropdownButtonFormField(
decoration: const InputDecoration(
labelText: "department",
border: OutlineInputBorder(),
errorStyle: TextStyle(
color: Colors.redAccent, fontSize: 15),
),
hint: const Text("select department"),
value: addRole,
onChanged: (String? newValue) {
setState(() {
addRole = newValue!;
});
},
validator: (value) =>
value == null ? 'field required' : null,
items: <String>[
'hr',
'dtp'
].map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
),
const SizedBox(
height: 20,
),
//
ElevatedButton(
style: ElevatedButton.styleFrom(
primary: Colors.red, // background
onPrimary: Colors.white, // foreground
),
onPressed: () {
bool isValid =
_formkey.currentState!.validate();
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(
content: Text("form is $isValid")));
},
child: const Text('User Add'),
),
const SizedBox(
height: 20,
),
],
),
),
)),
),
Center(
child: Text("Test"),
)
],
),
),
),
);
}
}

就我而言，问题出在项目列表中，其中某些值很长(字符串长度)。我已经以这种方式解决了

DropdownButtonFormField(
...
items: items
.map(
(e) => DropdownMenuItem(
value: e,
child: e.length > 30
? Text('${e[0].toUpperCase()}${e.substring(1, 30)}...')
: Text("${e[0].toUpperCase()}${e.substring(1)}"),
)).toList(),
)

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