为变量错误设置状态；这个小部件已经被卸载，所以状态不再有上下文（并且应该被认为是不存在的）
Set state for variable error; This widget has been unmounted, so the State no longer has a context (and should be considered defunct)
我是 Flutter 的新手，我有一个页面，我在搜索字段中输入两个输入，将它们放入不同的变量（_selectedYear 和 _selectedSem），并基于我的输入创建一个 url。
在创建两个搜索字段和 运行 时，如果我在第一个字段之前输入第二个字段，我没有错误，但如果我在第二个字段之前输入第一个字段，则会弹出此错误。
This widget has been unmounted, so the State no longer has a context (and should be
considered defunct). Consider canceling any active work during dispose or using the getter mounted to determine if the state is still active.
这是一个 screenshot 页面：
这是代码。
class _TestrState extends State<Testr> {
String _selectedYear;
String _selectedSem;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0,
backgroundColor: Colors.white,
title: const Text(
'Testr',
style: TextStyle(
color: Colors.black,
),
),
flexibleSpace: Container(
decoration: const BoxDecoration(
gradient: LinearGradient(
begin: Alignment.centerLeft,
end: Alignment.bottomRight,
colors: [Colors.green, Colors.limeAccent])),
),
),
body: Container(
child: SingleChildScrollView(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Container(
height: MediaQuery.of(context).size.height * 0.64,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.center,
children: [
const Padding(
padding: EdgeInsets.all(20.0),
child: Text(
'Select a Year',
style: TextStyle(fontSize: 16, color: Colors.blueGrey),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.symmetric(horizontal: 20),
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
boxShadow: [
BoxShadow(
color: Colors.grey.withOpacity(0.2),
blurRadius: 10,
offset: const Offset(0, 10),
),
],
),
child: SearchField(
hint: 'Search for Year',
searchInputDecoration: InputDecoration(
enabledBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Colors.blueGrey.shade200,
width: 1,
),
borderRadius: BorderRadius.circular(10),
),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
width: 2,
color: Colors.blue.withOpacity(0.8),
),
borderRadius: BorderRadius.circular(10),
),
),
maxSuggestionsInViewPort: 4,
itemHeight: 50,
suggestionsDecoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
),
onTap: (value) {
setState(() {
_selectedYear = value;
});
if (kDebugMode) {
print(value);
}
},
suggestions: const [
'Year One',
'Year Two',
'Year Three',
'Year Four',
],
),
),
const Padding(
padding: EdgeInsets.all(20.0),
child: Text(
'Select a Semester',
style: TextStyle(fontSize: 16, color: Colors.blueGrey),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.symmetric(horizontal: 20),
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
boxShadow: [
BoxShadow(
color: Colors.grey.withOpacity(0.2),
blurRadius: 10,
offset: const Offset(0, 10),
),
],
),
child: SearchField(
hint: 'Search for Semester',
searchInputDecoration: InputDecoration(
enabledBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Colors.blueGrey.shade200,
width: 1,
),
borderRadius: BorderRadius.circular(10),
),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
width: 2,
color: Colors.blue.withOpacity(0.8),
),
borderRadius: BorderRadius.circular(10),
),
),
maxSuggestionsInViewPort: 4,
itemHeight: 50,
suggestionsDecoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
),
onTap: (value) {
setState(() {
_selectedSem = value;
});
if (kDebugMode) {
print(value);
}
},
suggestions: const [
'Afghanistan',
'Turkey',
'Germany',
'France',
'Italy',
],
),
),
],
),
),
Container(
height: 90,
padding: const EdgeInsets.only(right: 20, left: 20, bottom: 20),
decoration: const BoxDecoration(
color: Colors.white,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
_selectedYear == null
? const Text(
'Select a Year and a Semester to Continue',
style:
TextStyle(fontSize: 14, color: Colors.blueGrey),
)
: Text(_selectedYear + "->" + _selectedSem,
style: TextStyle(
fontSize: 16,
color: Colors.grey.shade800,
fontWeight: FontWeight.w600)),
MaterialButton(
onPressed: () {
CreateURL(_selectedYear, _selectedSem);
},
color: Colors.black,
minWidth: 50,
height: 50,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(50),
),
padding: const EdgeInsets.all(0),
child: const Icon(
Icons.arrow_forward_ios,
color: Colors.blueGrey,
size: 24,
),
)
],
),
)
],
),
),
),
);
}
}
我试过将 setstate 放在 'if(mounted)' 中，但在查看其他类似问题后没有奏效。
我不确定，但一旦你尝试这种方式。首先，将值初始化为一个变量，然后刷新状态
_selectedYear = value!;
setState(() {});
或者如果您使用的是 flutter 2.5.3 或更高版本，那么您需要初始化变量或迁移到空安全。
我刚刚更改了变量初始化并且它起作用了。
String _selectedYear = "";
String _selectedSem = "";
并将此逻辑添加到 setState
setState(() {
_selectedSem = value!;
});
这对我有用，试试看
我是 Flutter 的新手，我有一个页面，我在搜索字段中输入两个输入，将它们放入不同的变量（_selectedYear 和 _selectedSem），并基于我的输入创建一个 url。
在创建两个搜索字段和 运行 时，如果我在第一个字段之前输入第二个字段，我没有错误，但如果我在第二个字段之前输入第一个字段，则会弹出此错误。
This widget has been unmounted, so the State no longer has a context (and should be considered defunct). Consider canceling any active work during dispose or using the getter mounted to determine if the state is still active.
这是一个 screenshot 页面：
这是代码。
class _TestrState extends State<Testr> {
String _selectedYear;
String _selectedSem;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
elevation: 0,
backgroundColor: Colors.white,
title: const Text(
'Testr',
style: TextStyle(
color: Colors.black,
),
),
flexibleSpace: Container(
decoration: const BoxDecoration(
gradient: LinearGradient(
begin: Alignment.centerLeft,
end: Alignment.bottomRight,
colors: [Colors.green, Colors.limeAccent])),
),
),
body: Container(
child: SingleChildScrollView(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Container(
height: MediaQuery.of(context).size.height * 0.64,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.center,
children: [
const Padding(
padding: EdgeInsets.all(20.0),
child: Text(
'Select a Year',
style: TextStyle(fontSize: 16, color: Colors.blueGrey),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.symmetric(horizontal: 20),
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
boxShadow: [
BoxShadow(
color: Colors.grey.withOpacity(0.2),
blurRadius: 10,
offset: const Offset(0, 10),
),
],
),
child: SearchField(
hint: 'Search for Year',
searchInputDecoration: InputDecoration(
enabledBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Colors.blueGrey.shade200,
width: 1,
),
borderRadius: BorderRadius.circular(10),
),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
width: 2,
color: Colors.blue.withOpacity(0.8),
),
borderRadius: BorderRadius.circular(10),
),
),
maxSuggestionsInViewPort: 4,
itemHeight: 50,
suggestionsDecoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
),
onTap: (value) {
setState(() {
_selectedYear = value;
});
if (kDebugMode) {
print(value);
}
},
suggestions: const [
'Year One',
'Year Two',
'Year Three',
'Year Four',
],
),
),
const Padding(
padding: EdgeInsets.all(20.0),
child: Text(
'Select a Semester',
style: TextStyle(fontSize: 16, color: Colors.blueGrey),
),
),
Container(
width: double.infinity,
margin: const EdgeInsets.symmetric(horizontal: 20),
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
boxShadow: [
BoxShadow(
color: Colors.grey.withOpacity(0.2),
blurRadius: 10,
offset: const Offset(0, 10),
),
],
),
child: SearchField(
hint: 'Search for Semester',
searchInputDecoration: InputDecoration(
enabledBorder: OutlineInputBorder(
borderSide: BorderSide(
color: Colors.blueGrey.shade200,
width: 1,
),
borderRadius: BorderRadius.circular(10),
),
focusedBorder: OutlineInputBorder(
borderSide: BorderSide(
width: 2,
color: Colors.blue.withOpacity(0.8),
),
borderRadius: BorderRadius.circular(10),
),
),
maxSuggestionsInViewPort: 4,
itemHeight: 50,
suggestionsDecoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(10),
),
onTap: (value) {
setState(() {
_selectedSem = value;
});
if (kDebugMode) {
print(value);
}
},
suggestions: const [
'Afghanistan',
'Turkey',
'Germany',
'France',
'Italy',
],
),
),
],
),
),
Container(
height: 90,
padding: const EdgeInsets.only(right: 20, left: 20, bottom: 20),
decoration: const BoxDecoration(
color: Colors.white,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
_selectedYear == null
? const Text(
'Select a Year and a Semester to Continue',
style:
TextStyle(fontSize: 14, color: Colors.blueGrey),
)
: Text(_selectedYear + "->" + _selectedSem,
style: TextStyle(
fontSize: 16,
color: Colors.grey.shade800,
fontWeight: FontWeight.w600)),
MaterialButton(
onPressed: () {
CreateURL(_selectedYear, _selectedSem);
},
color: Colors.black,
minWidth: 50,
height: 50,
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(50),
),
padding: const EdgeInsets.all(0),
child: const Icon(
Icons.arrow_forward_ios,
color: Colors.blueGrey,
size: 24,
),
)
],
),
)
],
),
),
),
);
}
}
我试过将 setstate 放在 'if(mounted)' 中，但在查看其他类似问题后没有奏效。
我不确定，但一旦你尝试这种方式。首先，将值初始化为一个变量，然后刷新状态
_selectedYear = value!;
setState(() {});
或者如果您使用的是 flutter 2.5.3 或更高版本，那么您需要初始化变量或迁移到空安全。
我刚刚更改了变量初始化并且它起作用了。
String _selectedYear = "";
String _selectedSem = "";
并将此逻辑添加到 setState
setState(() {
_selectedSem = value!;
});
这对我有用，试试看