小部件库捕获的异常在构建 HomePageScreen(dirty, state: _HomePageScreenState#3ae53) 时引发了以下 ArgumentError：答案

【问题标题】：Exception caught by widgets library The following ArgumentError was thrown building HomePageScreen(dirty, state: _HomePageScreenState#3ae53):小部件库捕获的异常在构建 HomePageScreen(dirty, state: _HomePageScreenState#3ae53) 时引发了以下 ArgumentError：
【发布时间】：2020-03-19 08:03:10
【问题描述】：

大家好，你们能帮我解决这个问题吗？我只是四处寻找并没有得到正确的答案，谢谢。

void _submit() {
  final form = formKey.currentState;
  if (form.validate()) {
    form.save();
    print(_username);
    print(_password);
    if (_username == "asdasd") {
      if (_password == "123") {
        Navigator.pushReplacement(
            this.context, MaterialPageRoute(builder: (context) => App()));
      } else {
        scaffoldKey.currentState.showSnackBar(SnackBar(
          content: Text("login Failed, please re-type properly"),
          backgroundColor: Colors.redAccent,
        )); // SnackBar
      }
    } else {
      scaffoldKey.currentState.showSnackBar(SnackBar(
        content: Text("Login Failed, please re-type properly"),
        backgroundColor: Colors.redAccent,
      ));
    }
  }
}

错误信息：

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following ArgumentError was thrown building HomePageScreen(dirty, state: _HomePageScreenState#3ae53):
Invalid argument(s)

The relevant error-causing widget was: 
  HomePageScreen file:///Users/andrehendrawan/Downloads/ican/lib/Screens/App.dart:20:5
When the exception was thrown, this was the stack: 
#0      _StringBase.+ (dart:core-patch/string_patch.dart:265:57)
#1      _HomePageScreenState._greetings (package:ican/Screens/homePageScreen.dart:237:19)
#2      _HomePageScreenState.build (package:ican/Screens/homePageScreen.dart:75:17)
#3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4334:27)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4223:15)
...

【问题讨论】：

标签： android flutter

【解决方案1】：

嗨，伙计们，顺便说一句，我刚刚解决了这个问题，我只是重建了我的整个 HomePageScreen 并用相同的小部件填充了 statefull 屏幕，然后我重新运行它并且错误消失了，我不知道为什么它可以工作

【讨论】：