flutter 中的共享首选项停止应用

如何解决flutter 中的共享首选项停止应用

我在作为启动画面制作的页面中调用共享首选项

  void initState() {
    super.initState();
    getPreferences().then((value){
      Timer(
        Duration(seconds: 2),(() => {
          Navigator.of(context).pushReplacement(new MaterialPageRoute(
              builder: (BuildContext context) => value))
        }),);
    });
  }

这是我的方法

   getPreferences() async {
    WidgetsFlutterBinding.ensureInitialized();//??**
    SharedPreferences prefs = await SharedPreferences.getInstance();//the same with home screen in the skip button
    bool loadingScreen=prefs.getBool('seen');
    print("loadingScreen = $loadingScreen");
    StatefulWidget _screen= LoginScr();
     if (loadingScreen == null|| loadingScreen == false){
       _screen = Tut();
     }
     else if (loadingScreen == true){
       userName = prefs.getString('userName');
       if(userName ==null||userName=="null") {
         print(userName+' userName in main');
         _screen = LoginScr();
       } else {
         print(userName +'userName in main');
         _screen = HomePage();
       }
     }
     return _screen;
  }

顺便说一句，我不知道这条线是什么 Widge,tsFlutterBinding.ensureInitialized();//??** 这是我的日志

正在执行热重启...正在将文件同步到设备 Android SDK 构建对于 x86... 在 1,776 毫秒内重新启动应用程序。我/颤振（8982）： loadingScreen = true E/Flutter ( 8982): [错误：Flutter/lib/ui/ui_dart_state.cc(177)] 未处理的异常： NoSuchMethodError: 在 null 上调用了方法“+”。 E/颤振 ( 8982）：接收器：空E/Flutter（8982）：尝试调用：+（“用户名在 main") E/Flutter ( 8982): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5) E/Flutter (8982): #1
_SplashSCRState.getPreferences (package:plaster/UI/SplashSCR.dart:138:24) E/Flutter (8982): E/颤振（8982）：#2
_SplashSCRState.initState (package:plaster/UI/SplashSCR.dart:26:5) E/Flutter (8982): #3 StatefulElement._firstBuild (package:Flutter/src/widgets/framework.dart:4765:58) E/Flutter ( 8982）：#4 ComponentElement.mount （包：Flutter/src/widgets/framework.dart:4601:5）E/Flutter（8982）： #5 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#6 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#7 SingleChildRenderObjectElement.mount (package:Flutter/src/widgets/framework.dart:6118:14) E/Flutter ( 8982）：#8 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#9 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#10 ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4652:16) E/Flutter ( 8982）：#11 Element.rebuild （包：Flutter/src/widgets/framework.dart:4343:5）E/Flutter（8982）： #12 ComponentElement._firstBuild (package:Flutter/src/widgets/framework.dart:4606:5) E/Flutter (8982): #13 ComponentElement.mount (package:Flutter/src/widgets/framework.dart:4601:5) E/Flutter (8982): #14 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#15 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#16 SingleChildRenderObjectElement.mount (package:Flutter/src/widgets/framework.dart:6118:14) E/Flutter ( 8982）：#17 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#18 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#19 SingleChildRenderObjectElement.mount (package:Flutter/src/widgets/framework.dart:6118:14) E/Flutter ( 8982）：#20 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#21 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#22 ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4652:16) E/Flutter ( 8982）：#23 StatefulElement.performRebuild (package:Flutter/src/widgets/framework.dart:4800:11) E/Flutter ( 8982）：#24 Element.rebuild （包：Flutter/src/widgets/framework.dart:4343:5）E/Flutter（8982）： #25 ComponentElement._firstBuild (package:Flutter/src/widgets/framework.dart:4606:5) E/Flutter (8982): #26 StatefulElement._firstBuild (package:Flutter/src/widgets/framework.dart:4791:11) E/Flutter ( 8982）：#27 ComponentElement.mount （包：Flutter/src/widgets/framework.dart:4601:5）E/Flutter（8982）： #28 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#29 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#30 SingleChildRenderObjectElement.mount (package:Flutter/src/widgets/framework.dart:6118:14) E/Flutter ( 8982）：#31 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#32 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#33 SingleChildRenderObjectElement.mount (package:Flutter/src/widgets/framework.dart:6118:14) E/Flutter ( 8982）：#34 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#35 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#36 ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4652:16) E/Flutter ( 8982）：#37 StatefulElement.performRebuild (package:Flutter/src/widgets/framework.dart:4800:11) E/Flutter ( 8982）：#38 Element.rebuild （包：Flutter/src/widgets/framework.dart:4343:5）E/Flutter（8982）： #39 ComponentElement._firstBuild (package:Flutter/src/widgets/framework.dart:4606:5) E/Flutter (8982): #40 StatefulElement._firstBuild (package:Flutter/src/widgets/framework.dart:4791:11) E/Flutter ( 8982）：#41 ComponentElement.mount （包：Flutter/src/widgets/framework.dart:4601:5）E/Flutter（8982）： #42 Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3569:14) E/Flutter ( 8982）：#43 Element.updateChild (package:Flutter/src/widgets/framework.dart:3327:18) E/Flutter ( 8982）：#44 ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4652:16) E/Flutter ( 8982): #45 元素.r

解决方法

您正在尝试打印日志：

print(userName + ' userName in main');

当 userName 为 null 时：

if (userName == null || userName == "null")

它引发了异常。修改print方法的用法ant再试。应该是这样的：

userName = prefs.getString('userName');
if(userName == null || userName == "null") {
  print('first start,userName in main is null');
  _screen = LoginScr();
} else {
  print('$userName is userName in main');
  _screen = HomePage();
}