flutter nosuchmethoderror类字符串没有实例getter“isnegative”

Question

我正在遵循一个教程，试图创建一个水平的SingleChildScrollView，它包含带有产品描述的对象和带有两个小数的货币+价格标签。实现NumberFormat.Currency方法返回一个错误：NosuchMethodeRorr类“String”没有实例getter“is negal”

有人能帮助理解为什么它不拉“价格”价值吗？如果我对其进行硬编码，并为最终的双倍价格赋值=IE:29.90；在AngeboteCard（）类中有，但在Angebote（）类中没有。

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:hotz/constants.dart';
import 'package:intl/intl.dart';
import 'package:intl/number_symbols.dart';

class Angebote extends StatelessWidget {
  const Angebote({
    Key key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      scrollDirection: Axis.horizontal,
      child: Row(
        children: <Widget>[
          AngeboteCard(
            image: "assets/images/pork_belly.png",
            product: "Schweinsbrust frisch",
            price: 29.90,
            press: () {},
          ),
        ],
      ),
    );
  }
}

class AngeboteCard extends StatelessWidget {
  const AngeboteCard({
    Key key,
    this.image,
    this.title,
    this.product,
    this.price,
    this.press,
  }) : super(key: key);
  final String image, title, product;
  final double price;
  final Function press;

  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return GestureDetector(
      onTap: press,
      child: Container(
        margin: EdgeInsets.only(
          left: kDefaultPadding,
          top: kDefaultPadding / 2,
          bottom: kDefaultPadding / 0.5,
          right: kDefaultPadding,
        ),
        width: size.width * 0.8,
        height: 300,
        child: Column(
          children: <Widget>[
            Image.asset(image),
            GestureDetector(
              onTap: press,
              child: Container(
                padding: EdgeInsets.all(kDefaultPadding / 2),
                decoration: BoxDecoration(
                  color: Colors.white,
                  borderRadius: BorderRadius.only(
                    bottomLeft: Radius.circular(10),
                    bottomRight: Radius.circular(10),
                  ),
                  boxShadow: [
                    BoxShadow(
                      offset: Offset(0, 10),
                      blurRadius: 50,
                      color: kPrimaryColour.withOpacity(0.23),
                    ),
                  ],
                ),
                child: Row(
                  children: <Widget>[
                    RichText(
                      text: TextSpan(
                        children: [
                          TextSpan(
                              text: "$title\n".toUpperCase(),
                              style: Theme.of(context).textTheme.button),
                          TextSpan(
                            text: "$product\n".toUpperCase(),
                            style: TextStyle(
                                color: kPrimaryColour.withOpacity(0.5)),
                          ),
                        ],
                      ),
                    ),
                    Spacer(),
                    Text(
                    NumberFormat.currency(locale: 'de_CH', decimalDigits: 2).format('$price'),
//                   'CHF ''$price',
                      style: Theme.of(context)
                          .textTheme
                          .button
                          .copyWith(color: kPrimaryColour),
                    )
                  ],
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

widgets库捕获的异常接收者：“null”尝试调用：isNegative

相关的导致错误的小部件是：AngeboteCard file：///users/nebojsa.kuzmanovic/development/flutterprojects/hotz/lib/screens/home/components/angebote.dart:29:11抛出异常时，这是堆栈:#0 object.nosuchmethod(dart:core-patch/object_patch.dart:54:5)#1 numberformat._signprefix（包:intl/src/intl/number_format.dart:786:30)#2/components/angebote.dart:107:80)#4 statelesselement.build（包:flutter/src/widgets/framework.dart:4569:28)...

Answer 1

所以你不能在。format函数中使用字符串，你需要使用一个数字（double或int)，我在代码中尝试了这种方法，并使用了正常的2位数：

Text(
   NumberFormat.currency(locale: 'de_CH').format(price),
   style: Theme.of(context)
       .textTheme
       .button
       .copyWith(color: kPrimaryColour),
   )