【发布时间】：2021-09-19 18:32:04
【问题描述】：
我是一名业余编码人员，正在做我的第一个 Flutter 项目。这是一个简单的每日单词应用程序，人们可以在其中写下单词的句子来记住它们。然后，该应用程序将这些句子存储在 ExpandedTile 中，其中单词作为标题，句子作为字幕。但是，我在手机上本地保存这些信息时遇到了一些问题。我已经修改了很多选项，并尝试了路径提供程序和共享首选项。这里的 words 对象是一个包含所有单词和含义的 Map，而 Savedwords 是一个以单词作为键，句子作为值的映射。当前使用共享首选项显示此错误：
E/flutter ( 1223): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: type String' is not a subtype of type 'List<String>'
E/flutter ( 1223): #0 _SavedprefState.addString.<anonymous closure>
package:to_dolist/widgets/sharedpreflist.dart:22
E/flutter ( 1223): #1 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:397:8)
E/flutter ( 1223): #2 _SavedprefState.addString
package:to_dolist/widgets/sharedpreflist.dart:22
E/flutter ( 1223): <asynchronous suspension>
E/flutter ( 1223):
E/flutter ( 1223): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: NoSuchMethodError: The getter 'iterator' was called on null.
E/flutter ( 1223): Receiver: null
E/flutter ( 1223): Tried calling: iterator
E/flutter ( 1223): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
E/flutter ( 1223): #1 _SavedprefState.getString
package:to_dolist/widgets/sharedpreflist.dart:30
E/flutter ( 1223): <asynchronous suspension>
E/flutter ( 1223):
我希望你们可以使用下面给出的代码帮助解决这个错误。如果这有助于为这个持久性问题获得更有效的解决方案，我在这里提供了更多必要的代码。我已经被这个问题困扰了几个月了，如果你能在这里给出编码的解决方案，我真的会帮助我。这是主要的 dart 文件
import 'package:flutter/material.dart';
import 'package:to_dolist/screens/HomePage.dart';
import './words.dart';
import './widgets/all.dart';
import './screens/secondscreen.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatefulWidget {
MyApp({Key key}) : super(key: key);
@override
State<StatefulWidget> createState() {
return MyAppState();
}
}
class MyAppState extends State<MyApp> {
var currentIndex = 0;
final saveword = TextEditingController();
var index = 0;
void nextword() {
saveword.clear();
setState(() {
if (index == words.length) {
//index == words.length;
} else {
index++;
}
});
}
void dispose() {
// Clean up the controller when the widget is disposed.
saveword.dispose();
super.dispose();
}
void prevword() {
saveword.clear();
setState(() {
if (index == 0) {
} else {
index--;
}
});
//return index;
}
void onTapped(int index) {
setState(() {
currentIndex = index;
});
}
@override
Widget build(BuildContext context) {
final List<Widget> screens = [
HomePage(index, nextword, prevword, saveword),
SecondPage(saveword)
];
return MaterialApp(
theme: ThemeData(),
home: Builder(
builder: (context) => Scaffold(
backgroundColor: Colors.grey[850],
appBar: AppBar(
iconTheme: IconThemeData(color: Colors.green),
title: RichText(
textAlign: TextAlign.left,
text: TextSpan(
style: TextStyle(
color: Colors.white,
fontSize: 50,
),
children: <TextSpan>[
TextSpan(text: 'Word of \n ', style: TextStyle()),
TextSpan(
text: ' The Day',
style: TextStyle(fontWeight: FontWeight.bold)),
],
),
),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.vertical(
bottom: Radius.circular(30),
),
),
toolbarHeight: 130,
centerTitle: true,
elevation: 4,
backgroundColor: Colors.grey,
),
body: screens[currentIndex],
bottomNavigationBar: BottomNavigationBar(
elevation: 100,
//backgroundColor: Colors.grey,
type: BottomNavigationBarType.shifting,
currentIndex: currentIndex,
items: const <BottomNavigationBarItem>[
BottomNavigationBarItem(
icon: Icon(Icons.today),
label: 'Word of The Day',
backgroundColor: Colors.grey),
BottomNavigationBarItem(
icon: Icon(Icons.list),
label: 'History',
backgroundColor: Colors.grey),
],
onTap: onTapped,
),
floatingActionButtonLocation:
FloatingActionButtonLocation.miniCenterDocked,
floatingActionButton: Fab(saveword, index),
)));
}
}
这是主页：
import 'package:flutter/material.dart';
import 'package:to_dolist/widgets/all.dart';
@override
class HomePage extends StatelessWidget {
//const ({ Key? key }) : super(key: key);
final int index;
final Function nextword;
final Function prevword;
final control;
HomePage(this.index, this.nextword, this.prevword, this.control);
@override
Widget build(BuildContext context) {
return SingleChildScrollView(
child: Column(
children: <Widget>[
SizedBox(
height: 20,
width: 500,
),
Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12),
color: Colors.grey,
),
child: WordColumn(index),
alignment: Alignment.center,
margin: new EdgeInsets.only(left: 20.0, right: 20.0, top: 20.0),
padding: new EdgeInsets.all(20.0),
),
Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(12),
color: Colors.grey,
),
alignment: Alignment(0.0, 0.0),
margin: new EdgeInsets.all(20.0),
padding: new EdgeInsets.all(35.0),
child: TextField(
style: TextStyle(color: Colors.white),
controller: control,
onChanged: (text) => {},
keyboardType: TextInputType.multiline,
minLines: 2,
maxLines: 30,
),
),
NavigateWords(nextword, prevword),
SizedBox(
height: 50,
width: double.infinity,
),
/*ElevatedButton(
child: Text('history'),
onPressed: Storage.readCounter ,
)*/
],
),
);
}
}
还有第二页的dart文件：
import 'package:flutter/material.dart';
import 'package:to_dolist/words.dart';
import './fab.dart';
import 'package:shared_preferences/shared_preferences.dart';
class Savedpref extends StatefulWidget {
TextEditingController control;
Savedpref(this.control);
//const Savedpref({ Key? key }) : super(key: key);
@override
_SavedprefState createState() => _SavedprefState();
}
class _SavedprefState extends State<Savedpref> {
Future<SharedPreferences> savedlist = SharedPreferences.getInstance();
var written, read, values;
List<Widget> savedhistory = [];
Future<Null> addString() async {
final SharedPreferences prefs = await savedlist;
Fab.savedwords
.forEach((key, value) => {prefs.setStringList(key, value)});
setState(() {});
}
Future<Null> getString() async {
final SharedPreferences prefs = await savedlist;
var keys = prefs.getKeys();
keys.forEach((element) => {read.add(element)});
for (var k in read) {
values.add(prefs.get(k));
}
for (var j = 0; j <= keys.length; j++) {
savedhistory.add(new ExpansionTile(
title: Text(read[j], style: TextStyle(color: Colors.white)),
subtitle: Text(words[j].value, style: TextStyle(color: Colors.white)),
children: [
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(values[j]),
],
)
],
));
}
setState(() {});
//keys.add(prefs.getKeys());
//prefs.
}
@override
Widget build(BuildContext context) {
@override
void initState() {
super.initState();
written = [];
read = [];
}
return Stack(children: [
ListView.separated(
reverse: true,
shrinkWrap: true,
separatorBuilder: (context, i) => Container(
//color: Colors.greenAccent,
width: double.infinity,
height: 8,
),
itemCount: savedhistory.length,
itemBuilder: (context, i) => Dismissible(
key: UniqueKey(),
onDismissed: (direction) {
setState(() {
savedhistory.removeAt(i);
});
},
child: Container(
margin: EdgeInsets.all(10),
padding: EdgeInsets.all(5),
decoration: BoxDecoration(
color: Colors.grey,
borderRadius: BorderRadius.all(Radius.circular(20))),
child: savedhistory[i],
//padding: EdgeInsets.all(8.0),
),
/* read == null
? []
: read.map((e) => ExpansionTile(
title: Text(e),
subtitle: Text(e),
)), */
)),
Align(
alignment: Alignment.bottomRight,
child: GestureDetector(
onLongPress: () => getString(),
child: FloatingActionButton(
child: Icon(Icons.replay_outlined),
onPressed: addString,
)),
)
]);
}
}
这是浮动操作按钮 (Fab) 小部件代码：
import 'package:to_dolist/words.dart';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'dart:io';
import 'package:to_dolist/widgets/sharedpreflist.dart';
//import 'dart:convert';
class Fab extends StatelessWidget {
static List history = <Widget>[];
static Map savedwords = Map();
/* void save1() {
savedwords[words[index].key] = control.text;
Storage.writeCounter();
}*/
void save() {
savedwords[words[index].key] = control.text;
//addString();
//print(savedwords);*/
/*history.add(new ExpansionTile(
title: Text(
words[index].key,
style: TextStyle(color: Colors.white),
),
subtitle: Text(words[index].value, style: TextStyle(color: Colors.white)),
expandedCrossAxisAlignment: CrossAxisAlignment.start,
backgroundColor: Colors.grey,
children: [
Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(control.text),
],
)
],
//tileColor: Colors.white,
//shape: RoundedRectangleBorder(
//side: BorderSide(width: 1), borderRadius: BorderRadius.circular(20)),
)); */
}
//final Function save;
final int index;
final control;
Fab(this.control, this.index);
@override
Widget build(BuildContext context) {
return Container(
child: FloatingActionButton.extended(
onPressed: save,
label: const Text('Save'),
icon: const Icon(Icons.save),
backgroundColor: Colors.green[200],
),
);
}
}
【问题讨论】：
标签： flutter flutter-dependencies