颤动中的共享首选项停止应用程序

Question

我在作为初始屏幕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... 将文件同步到构建的设备 Android SDK 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）：接收者：null 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 (包:flutter/src/widgets/framework.dart:4765:58) E/flutter ( 8982): #4 组件元素.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 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #7 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:6118:14) E/flutter ( 8982): #8 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3569:14) E/flutter ( 8982): #9 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #10 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4652:16) E/flutter ( 8982): #11 元素重建 （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 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #16 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:6118:14) E/flutter ( 8982): #17 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3569:14) E/flutter ( 8982): #18 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #19 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:6118:14) E/flutter ( 8982): #20 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3569:14) E/flutter ( 8982): #21 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982）：#22 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4652:16) E/flutter ( 8982): #23 StatefulElement.performRebuild (包:flutter/src/widgets/framework.dart:4800:11) E/flutter ( 8982): #24 元素重建 （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 组件元素.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 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #30 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:6118:14) E/flutter ( 8982): #31 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3569:14) E/flutter ( 8982):#32 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982): #33 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:6118:14) E/flutter ( 8982):#34 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3569:14) E/flutter ( 8982): #35 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982）：#36 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4652:16) E/flutter ( 8982）：#37 StatefulElement.performRebuild (包:flutter/src/widgets/framework.dart:4800:11) E/flutter ( 8982): #38 元素重建 （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 组件元素.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 元素.updateChild (包:flutter/src/widgets/framework.dart:3327:18) E/flutter ( 8982）：#44 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4652:16) E/flutter ( 8982): #45 元素.r

Answer 1

您尝试打印日志：

print(userName + ' userName in main');

当userName 是null：

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

它会引发异常。修改print方法用法ant再试一次。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();
}