用于空值错误的空检查运算符

Question

这个问题的原因是什么？ 当我点击按钮显示 toast 时，会出现此消息

在处理手势时引发以下 _CastError： 用于空值的空检查运算符

*当异常被抛出时，这是堆栈： showToastWidget（包：flutter_styled_toast/src/styled_toast.dart:268:22）

 home: Scaffold(
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            showToast(txt,
                context: context,
                animation: StyledToastAnimation.slideFromLeft,
                reverseAnimation: StyledToastAnimation.slideToBottom,
                position: StyledToastPosition(
                align: Alignment.bottomCenter, offset: 55),
                animDuration: Duration(milliseconds: 300),
                duration: Duration(seconds: 2),
                curve: Curves.easeInOutBack,
                reverseCurve: Curves.elasticIn,
                backgroundColor: Color.fromRGBO(191, 21, 35, 0.5),
                textStyle: TextStyle(fontSize: 20, color: Colors.white));
          },
          child: const Icon(Icons.add),
        ),
        appBar: AppBar(title: Text('Flutter Code Sample')),
        body: const Center(
          child: MyStatelessWidget(),
        ),
      ),
    );
  }
}

Answer 1

答案：

import 'package:flutter/material.dart';

import 'dialogPage.dart';

void main() => runApp(MyApp());

/// This is the main application widget.
class MyApp extends StatelessWidget {

  MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home:DialogPage() ,
    );
  }
}

   return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          showToast(txt,
              context: context,
              animation: StyledToastAnimation.slideFromLeft,
              reverseAnimation: StyledToastAnimation.slideToBottom,
              position: const StyledToastPosition(
                  align: Alignment.bottomCenter, offset: 55),
              animDuration: Duration(milliseconds: 300),
              duration: const Duration(seconds: 2),
              curve: Curves.easeInOutBack,
              reverseCurve: Curves.elasticIn,
              backgroundColor: Color.fromRGBO(191, 21, 35, 0.5),
              textStyle: TextStyle(fontSize: 20, color: Colors.white));
        },
        child: const Icon(Icons.add),
      ),
      appBar: AppBar(title: Text('Flutter Code Sample')),
      body: const Center(
        child: MyStatelessWidget(),
      ),
    );