【发布时间】：2020-05-08 04:42:39
【问题描述】：
我正在尝试制作一个滑块来放大和缩小字体，但我遇到了这个错误。
E/flutter (11441): [错误:flutter/lib/ui/ui_dart_state.cc(157)] 未处理的异常：NoSuchMethodError：方法“setString”是 在 null 上调用。
E/flutter (11441)：接收器：null
E/flutter (11441)：尝试调用：setString("fontSizeArabic", “23.99652777777778”）
E/flutter (11441): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
E/flutter (11441): #1 SettingsHelpers.fontSizeArabic （包：alquranalkareem/helper/settings_helpers.dart:20:17）
E/flutter (11441): #2 _QuranShowState._showTafseer.. （包：alquranalkareem/module/quran/show.dart:881:32）
E/flutter (11441): #3 _SliderState._handleChanged (包:flutter/src/material/slider.dart:453:14)
E/flutter (11441): #4 _RenderSlider._startInteraction (包:flutter/src/material/slider.dart:982:7)
E/flutter (11441): #5 _RenderSlider._handleTapDown (包:flutter/src/material/slider.dart:1031:50)
E/颤振 (11441)：#6
TapGestureRecognizer.handleTapDown。 (包:flutter/src/gestures/tap.dart:463:51)E/flutter (11441): #7 GestureRecognizer.invokeCallback (包:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (11441): #8 TapGestureRecognizer.handleTapDown (包:flutter/src/gestures/tap.dart:463:11)
E/flutter (11441): #9 BaseTapGestureRecognizer._checkDown (包:flutter/src/gestures/tap.dart:256:5)
E/flutter (11441): #10 BaseTapGestureRecognizer.didExceedDeadline (包:flutter/src/gestures/tap.dart:227:5)
E/颤振 (11441)：#11
PrimaryPointerGestureRecognizer.didExceedDeadlineWithEvent (包:flutter/src/gestures/recognizer.dart:496:5)E/颤振 (11441)：#12
PrimaryPointerGestureRecognizer.addAllowedPointer。 (包:flutter/src/gestures/recognizer.dart:449:40)E/flutter (11441): #13 _rootRun (dart:async/zone.dart:1122:38)
E/flutter (11441): #14 _CustomZone.run (dart:async/zone.dart:1023:19)
E/flutter (11441): #15 _CustomZone.runGuarded (dart:async/zone.dart:925:7)
E/flutter (11441)：#16 _CustomZone.bindCallbackGuarded。 (dart:async/zone.dart:965:23)
E/flutter (11441): #17 _rootRun (dart:async/zone.dart:1126:13)
E/flutter (11441): #18 _CustomZone.run (dart:async/zone.dart:1023:19)
E/flutter (11441)：#19 _CustomZone.bindCallback。 (dart:async/zone.dart:949:23)
E/flutter (11441)：#20 Timer._createTimer。 (dart:async-patch/timer_patch.dart:23:15)
E/flutter (11441): #21 _Timer._runTimers (dart:isolate-patch/timer_impl.dart:384:19)
E/flutter (11441): #22 _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:418:5)
E/flutter (11441): #23 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:174:12)
你有解决问题的办法吗？
settings_helpers
import 'dart:convert';
import 'dart:ui';
import 'package:quiver/strings.dart';
import 'package:shared_preferences/shared_preferences.dart';
class SettingsHelpers {
static SettingsHelpers _instance;
static SettingsHelpers get instance {
if (_instance == null) {
_instance = SettingsHelpers();
}
return _instance;
}
SharedPreferences prefs;
Future fontSizeArabic(double fontSize) async {
await prefs.setString('fontSizeArabic', fontSize.toString());
}
static const double minFontSizeArabic = 22;
double get getFontSizeArabic {
String fontSizeString = prefs.getString('fontSizeArabic');
return double.tryParse(fontSizeString ?? minFontSizeArabic.toString());
}
Future setLocale(Locale locale) async {
var map = {
'languageCode': locale.languageCode,
};
var json = jsonEncode(map);
await prefs.setString('locale', json);
}
Locale getLocale() {
var json = prefs.getString('locale');
if (isBlank(json)) {
return Locale('en');
}
var mapJson = jsonDecode(json);
var locale = Locale(mapJson["languageCode"]);
return locale;
}
Future init() async {
prefs = await SharedPreferences.getInstance();
}
}
_showTafseer
Widget _showTafseer(int pageNum) {
TafseerRepository tafseerRepository = new TafseerRepository();
return FutureBuilder<List<Ayat>>(
future: tafseerRepository.getPageTafseer(pageNum),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.done) {
List<Ayat> ayat = snapshot.data;
return Padding(
padding: EdgeInsets.symmetric(horizontal: 16.0),
child: Column(
children: <Widget>[
Container(
color: Theme.of(context).primaryColorLight,
child: Row(
children: <Widget>[
Slider(
min: SettingsHelpers.minFontSizeArabic,
max: maxFontSizeArabic,
value: fontSizeArabic,
activeColor: Theme.of(context).hoverColor,
inactiveColor: Theme.of(context).primaryColorDark,
onChanged: (double value) async {
await SettingsHelpers.instance
.fontSizeArabic(value);
setState(
() {
fontSizeArabic = value;
},
);
_myEventBus.eventBus.fire(
FontSizeEvent()
..arabicFontSize = value
);
},
),
Container(
decoration: BoxDecoration(
color: Theme.of(context).hoverColor,
borderRadius: BorderRadius.only(
topLeft: Radius.circular(5.0),
topRight: Radius.circular(5.0),
bottomLeft: Radius.circular(5.0),
bottomRight: Radius.circular(5.0),
)
),
alignment: Alignment.center,
child: Padding(
padding: const EdgeInsets.all(4.0),
child: Text('${fontSizeArabic.toInt()}',
style: TextStyle(
fontSize: 20,
color: Theme.of(context).primaryColorLight)),
),
),
],
),
),
Container(
// width: 300.0,
height: 500.0,
child: ListView.builder(
itemCount: ayat.length,
itemBuilder: (context, position) {
Ayat aya = ayat[position];
List<String> tafseer = aya.tafsser.split("))");
return Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Container(
decoration: BoxDecoration(
color: Theme.of(context).backgroundColor,
borderRadius: BorderRadius.only(
topRight: Radius.circular(8.0),
topLeft: Radius.circular(8.0)
)
),
child: Padding(
padding: const EdgeInsets.all(4.0),
child: Text(
"﴿${tafseer.first}﴾",
textAlign: TextAlign.center,
style: TextStyle(
fontFamily: "Uthmanic",
fontWeight: FontWeight.w500,
fontSize: fontSizeArabic
),
),
),
),
Padding(
padding: const EdgeInsets.only(top: 16.0, bottom: 8.0),
child: Text(
"${tafseer.last.trim()}",
textAlign: TextAlign.justify,
style: TextStyle(
color: Theme.of(context).hoverColor,
fontFamily: 'naskh',
fontWeight: FontWeight.w100,
fontSize: fontSizeArabic
),
),
),
Divider()
],
);
}),
),
],
),
);
} else {
return Center(
child: CircularProgressIndicator(),
);
}
},
);
}
【问题讨论】：