祝大家有美好的一天。所以我對顫動相當陌生，我有一個頁面，我在一個搜索欄位中接受兩個輸入，將它們放在不同的變數（_selectedYear 和 _selectedSem）中，并根據輸入創建一個 url。在創建兩個搜索欄位并運行它時，如果我在第一個欄位之前輸入第二個欄位，我沒有錯誤，但如果我在第二個欄位之前輸入第一個欄位，則會彈出此錯誤。
此小部件已卸載，因此 State 不再具有背景關系（應視為已失效）。考慮在 dispose 期間取消任何活動的作業，或使用安裝的 getter 來確定狀態是否仍處于活動狀態。
這是頁面的螢屏截圖。點擊這里
這是代碼。
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,
),
)
],
),
)
],
),
),
),
);
}
}
我嘗試將 setstate 置于“if(mounted)”中，但在查看其他類似問題后卻沒有用。
有人介意幫我嗎？
uj5u.com熱心網友回復：
我只是更改了變數初始化并且它起作用了。
String _selectedYear = "";
String _selectedSem = "";
并將此邏輯添加到 setState
setState(() {
_selectedSem = value!;
});
這對我有用，試試看
uj5u.com熱心網友回復：
我不確定，但一旦你嘗試這種方式。首先，將值初始化為一個變數，然后重繪 狀態
_selectedYear = value!;
setState(() {});
或者，如果您使用的是 Flutter 2.5.3 或更高版本，則需要初始化變數或遷移到 null 安全性。
轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/459957.html
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