搜索委托，当我点击搜索按钮时，它会显示带有错误子项的红屏！ =空
Posted
技术标签:
【中文标题】搜索委托，当我点击搜索按钮时，它会显示带有错误子项的红屏！ =空【英文标题】：Search delegate , When I click on Search button it shows red screen with error child! =null 【发布时间】：2020-12-07 17:49:31 【问题描述】：我通过搜索委托创建了一个搜索选项，但是当我单击搜索按钮时，它显示红色屏幕并显示此错误“以下断言被抛出构建 _SearchPage(dirty, dependencies: [_LocalizationsScope-[GlobalKey#69e74], _InheritedTheme] , state: _SearchPageState#72bb6): 'package:flutter/src/widgets/basic.dart': 断言失败: line 6938 pos 15: 'child != null': is not true.
import 'package:flutter/material.dart';
import 'package:grk_001/screen/main_screen.dart';
import 'widgets/entry_item.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'package:grk_001/screen/favourite_screen.dart';
import 'package:grk_001/Provider/Auth.dart';
import 'package:provider/provider.dart';
import 'package:grk_001/Provider/cart.dart';
import 'package:grk_001/widgets/badge.dart';
import 'package:grk_001/screen/cart_screen.dart';
import 'package:grk_001/widgets/drawer.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:grk_001/models/main_screen_categories_entry.dart';
class HomeScreen extends StatefulWidget
static const String routename = 'homescreen';
@override
_HomeScreenState createState() => _HomeScreenState();
class _HomeScreenState extends State<HomeScreen>
final GlobalKey<ScaffoldState> _scaffoldkey = GlobalKey<ScaffoldState>();
FirebaseUser Loggedinuser;
@override
void didChangeDependencies()
// TODO: implement didChangeDependencies
Future.delayed(Duration.zero).then((_) async
await Provider.of<Auth>(context, listen: false).getcurrentuser();
);
super.didChangeDependencies();
@override
Widget build(BuildContext context)
final devicesize = MediaQuery.of(context).size;
return SafeArea(
child: Scaffold(
key: _scaffoldkey,
appBar: AppBar(
leading: IconButton(
onPressed: ()
_scaffoldkey.currentState.openDrawer();
,
icon: Icon(
Icons.list,
color: Colors.white,
size: 35.0,
),
),
bottom: PreferredSize(
preferredSize: const Size.fromHeight(50.0),
child: Container(
padding: const EdgeInsets.all(8.0),
child: Row(
children: <Widget>[
const SizedBox(
width: 10.0,
),
Expanded(
child: GestureDetector(
onTap: ()
_scaffoldkey.currentState.openEndDrawer();
,
child: Container(
padding: const EdgeInsets.all(8.0),
alignment: Alignment.center,
height: 40.0,
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.circular(5.0),
),
child: Text(
'Categories',
),
),
),
),
],
),
),
),
title: Text('HomeScreen'),
actions: <Widget>[
IconButton(
icon: Icon(Icons.search),
onPressed: ()
showSearch(context: context, delegate: DataSearch());
,
),
IconButton(
icon: Icon(
FontAwesomeIcons.heart,
size: 30.0,
),
tooltip: 'My Wish List',
onPressed: ()
Navigator.pushNamed(context, FavouriteScreen.routename);
,
),
IconButton(
icon: Icon(
Icons.notifications,
size: 30.0,
),
tooltip: 'My Notifications',
onPressed: () ,
),
Consumer<Cart>(
builder: (_, cartdata, ch) => Badge(
child: ch,
value: cartdata.itemcount.toString(),
),
child: IconButton(
onPressed: ()
Navigator.pushNamed(context, CartScreen.routename);
,
icon: Icon(
Icons.shopping_cart,
size: 40.0,
),
),
),
],
),
body: MainScreen(),
// body: CategoryScreen(),
endDrawer: Drawer(
child: Column(
children: <Widget>[
Container(
color: Color(0XFFFF4081),
height: devicesize.height * 0.10,
child: DrawerHeader(
margin: EdgeInsets.zero,
child: InkWell(
onTap: ()
Navigator.of(context).pop();
,
child: Row(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Icon(
Icons.apps,
color: Colors.white,
),
SizedBox(
width: 10.0,
),
Text(
'Categories',
style:
TextStyle(color: Colors.white, fontSize: 20.0),
),
],
),
)
// child: Text('Categories'),
),
),
Container(
height: devicesize.height * 0.85,
child: ListView.builder(
itemBuilder: (context, index) => EntryItem(data[index]),
itemCount: data.length,
),
)
],
),
),
drawer: Container(
width: devicesize.width * 0.65,
child: DrawerItem(devicesize, context),
),
),
);
class DataSearch extends SearchDelegate<String>
final statelist = [
'Andaman and Nicobar Islands',
' Andhra Pradesh',
'Arunachal Pradesh',
'Assam',
'Bihar',
'Chandigarh ',
'Chhattisgarh',
'Dadra and Nagar Havel',
'Daman and Diu',
'Delhi',
'Goa',
'Gujrat',
'Haryana',
'Himachal Pradesh',
'Uttar Pradesh',
'Uttarakhand',
'West Bengal',
'Sikkim',
'Meghalya',
'Mizoram',
];
final recentlist = ['Modingar', 'Ghaziabad', 'Merrut', 'Hapur', 'Delhi'];
@override
List<Widget> buildActions(BuildContext context)
// action for app bar
return [
IconButton(
onPressed: ()
query = "";
,
icon: Icon(Icons.clear),
)
];
@override
Widget buildLeading(BuildContext context)
// leading icon on the left of the app bar
return IconButton(
icon: AnimatedIcon(
icon: AnimatedIcons.menu_arrow,
progress: transitionAnimation,
),
onPressed: ()
close(context, null);
,
);
@override
Widget buildResults(BuildContext context)
// TODO: implement buildResults
return Container(
height: 150.0,
child: Card(
color: Colors.red,
shape: StadiumBorder(),
child: Text(query),
),
);
@override
Widget buildSuggestions(BuildContext context)
// TODO: implement buildSuggestions
final suggestionList = query.isEmpty
? recentlist
: statelist.where((element) => element.startsWith(query)).toList();
ListView.builder(
itemBuilder: (context, index) => ListTile(
onTap: ()
showResults(context);
,
title: RichText(
text: TextSpan(
text: suggestionList[index].substring(0, query.length),
style: TextStyle(
color: Colors.black,
fontWeight: FontWeight.bold,
),
children: [
TextSpan(
text: suggestionList[index].substring(query.length),
style: TextStyle(color: Colors.grey))
]),
)),
itemCount: suggestionList.length,
);
【问题讨论】：
【参考方案1】：您可以在下面复制粘贴运行完整代码
你需要buildSuggestions中的return关键字
你可以return ListView.builder
代码sn-p
@override
Widget buildSuggestions(BuildContext context)
// TODO: implement buildSuggestions
final suggestionList = query.isEmpty
? recentlist
: statelist.where((element) => element.startsWith(query)).toList();
return ListView.builder(
工作演示
完整代码
import 'package:flutter/material.dart';
void main()
runApp(MyApp());
class MyApp extends StatelessWidget
@override
Widget build(BuildContext context)
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
class MyHomePage extends StatefulWidget
MyHomePage(Key key, this.title) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
class _MyHomePageState extends State<MyHomePage>
int _counter = 0;
void _incrementCounter()
setState(()
_counter++;
);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(title: Text(widget.title), actions: <Widget>[
IconButton(
icon: Icon(Icons.search),
onPressed: ()
showSearch(context: context, delegate: DataSearch());
,
),
]),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
class DataSearch extends SearchDelegate<String>
final statelist = [
'Andaman and Nicobar Islands',
' Andhra Pradesh',
'Arunachal Pradesh',
'Assam',
'Bihar',
'Chandigarh ',
'Chhattisgarh',
'Dadra and Nagar Havel',
'Daman and Diu',
'Delhi',
'Goa',
'Gujrat',
'Haryana',
'Himachal Pradesh',
'Uttar Pradesh',
'Uttarakhand',
'West Bengal',
'Sikkim',
'Meghalya',
'Mizoram',
];
final recentlist = ['Modingar', 'Ghaziabad', 'Merrut', 'Hapur', 'Delhi'];
@override
List<Widget> buildActions(BuildContext context)
// action for app bar
return [
IconButton(
onPressed: ()
query = "";
,
icon: Icon(Icons.clear),
)
];
@override
Widget buildLeading(BuildContext context)
// leading icon on the left of the app bar
return IconButton(
icon: AnimatedIcon(
icon: AnimatedIcons.menu_arrow,
progress: transitionAnimation,
),
onPressed: ()
close(context, null);
,
);
@override
Widget buildResults(BuildContext context)
// TODO: implement buildResults
return Container(
height: 150.0,
child: Card(
color: Colors.red,
shape: StadiumBorder(),
child: Text(query),
),
);
@override
Widget buildSuggestions(BuildContext context)
// TODO: implement buildSuggestions
final suggestionList = query.isEmpty
? recentlist
: statelist.where((element) => element.startsWith(query)).toList();
return ListView.builder(
itemBuilder: (context, index) => ListTile(
onTap: ()
showResults(context);
,
title: RichText(
text: TextSpan(
text: suggestionList[index].substring(0, query.length),
style: TextStyle(
color: Colors.black,
fontWeight: FontWeight.bold,
),
children: [
TextSpan(
text: suggestionList[index].substring(query.length),
style: TextStyle(color: Colors.grey))
]),
)),
itemCount: suggestionList.length,
);
【讨论】：
以上是关于搜索委托，当我点击搜索按钮时，它会显示带有错误子项的红屏！ =空的主要内容，如果未能解决你的问题，请参考以下文章