Flutter错误，渲染库捕获异常

Question

我的代码之前运行良好，然后当我运行 flutter 升级并下载最新版本时，每次我尝试按下按钮移动到下一页。我收到“渲染库错误捕获的异常。

这是我得到的错误

 ════════ Exception caught by rendering library ═════════════════════════════════
 Null check operator used on a null value
 The relevant error-causing widget was
 PageView
 lib\menu_frame.dart:59 
 ════════════════════════════════════════════════════════════════════════════════
 E/flutter ( 5787): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: Null check 
 operator used on a null value.

这是我为那个特定页面准备的代码

  class MenuFrame extends StatelessWidget {
  PageController pageController = PageController();

 @override
 Widget build(BuildContext context) {
return Material(
  child: Container(
    child: Column(
      children: <Widget>[
        SafeArea(
          child: Padding(
            padding: EdgeInsets.symmetric(horizontal: 28.0, vertical: 40.0),
            child: Column(
              children: <Widget>[
                Icon(
                  FontAwesomeIcons.heartBroken,
                  color: Color.fromRGBO(245, 48, 111, 1.0),
                  size: 60.0,
                ),
                Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text(
                      'VORTEX',
                      style: TextStyle(
                        fontSize: 38.0,
                        fontWeight: FontWeight.bold,
                        color: Color.fromRGBO(245, 48, 111, 1.0),
                      ),
                    ),
                    Text(
                      'FITNESS',
                      style: TextStyle(
                        fontSize: 38.0,
                        fontWeight: FontWeight.bold,
                      ),
                    ),
                  ],
                ),
                Text(
                  'Find your passion for fitness!',
                  style: TextStyle(color: Colors.white, fontSize: 18.0),
                  textAlign: TextAlign.center,
                ),
                //        SizedBox(
                //        height: 85.0,
                //    ),
              ],
            ),
          ),
        ),
        Expanded(
          child: PageView(
          controller: pageController,
           //physics: NeverScrollableScrollPhysics(),
            children: <Widget>[
              HomeSignInWidget(
                goToSignIn: () {
                  pageController.animateTo(1,
                      duration: Duration(milliseconds: 200),
                      curve: Curves.easeIn);
                },
                goToSignUp: () {
                  pageController.animateTo(2,
                      duration: Duration(milliseconds: 200),
                      curve: Curves.easeIn);
                },
              ),
              SignIn(),
              CreateLogin(
                cancelBackToHome: () {
                  pageController.animateTo(0,
                      duration: Duration(milliseconds: 200),
                      curve: Curves.easeIn);
                },
              ),
            ],
          ),
        ),
      ],
    ),
    decoration: BoxDecoration(
        gradient: LinearGradient(
            begin: Alignment.topCenter,
            end: Alignment.bottomCenter,
            colors: [
          Color.fromRGBO(255, 123, 67, 1.0),
          Color.fromRGBO(245, 50, 111, 1.0),
        ])),
  ),
);
}
}

虽然我刚刚升级到最新版本，但我似乎无法弄清楚哪里出了问题？？

Answer 1

那是因为 null safety 来自 Flutter 2.0

的更新

有2个方案可以解决这个问题

第一

您将迁移 null safety

的所有代码

第二

在 pubspec.yaml 中降级您的 sdk 环境版本。示例：sdk: ">=2.10.0 <3.0.0"

你可以选择使用哪一个，如果你想使用空安全选择第一个，如果你不想使用空安全选择第二个

希望这对您有所帮助。

Flutter错误，渲染库捕获异常

Flutter error, Exception caught by rendering library

render

dart

flutter