按下时购物车计数器不更新值，没有显示错误

Posted 2023-02-23

【中文标题】按下时购物车计数器不更新值，没有显示错误

【英文标题】：Shopping Cart Counter not updating value when pressed, no Error is shown for the matter

【发布时间】：2021-09-19 23:27:01

【问题描述】：

我的应用程序中有一个购物车计数器的小代码，在运行应用程序时，它不会在按下添加或删除按钮（+ 和 - 图标）时更新，尽管我为它们分配了功能，没有错误显示为什么会发生这种情况......

这是计数器的代码：

    import 'package:flutter/material.dart';

class CartCounter extends StatefulWidget 
  @override
  _CartCounterState createState() => _CartCounterState();


class _CartCounterState extends State<CartCounter> 
  int numOfItems = 0;

  @override
  Widget build(BuildContext context) 
    return Row(
      children: <Widget>[
        buildOutlineButton(
          icon: Icons.remove,
          press: () 
            if (numOfItems > 0) 
              setState(() 
                numOfItems--;
              );
            
          ,
        ),
        Padding(
          padding: const EdgeInsets.symmetric(horizontal: kDefaultPaddin / 2),
          child: Text(
            // if our item is less  then 10 then  it shows 01 02 like that
            numOfItems.toString().padLeft(2, "0"),
            style: Theme.of(context).textTheme.headline6,
          ),
        ),
        buildOutlineButton(
            icon: Icons.add,
            press: () 
              if (numOfItems < 10) 
                setState(() 
                  numOfItems++;
                );
              
            ),
      ],
    );
  

  SizedBox buildOutlineButton(
      required IconData icon, required Function press) 
    return SizedBox(
      width: 40,
      height: 32,
      child: OutlinedButton(
        style: OutlinedButton.styleFrom(
          padding: EdgeInsets.zero,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(13.0)),
        ),
        onPressed: press(),
        child: Icon(icon),
      ),
    );
  

这是我调用 Cart Counter 类的代码，它还有一个运行良好的评分栏：

    class CounterWithRateBar extends StatefulWidget 
  @override
  _CounterWithRateBarState createState() => _CounterWithRateBarState();


class _CounterWithRateBarState extends State<CounterWithRateBar> 
  // const CounterWithRateBar(
  //   Key? key,
  // ) : super(key: key);
  late double _rating;
  int _ratingBarMode = 1;
  double _initialRating = 2.0;
  IconData? _selectedIcon;

  @override
  void initState() 
    super.initState();
    _rating = _initialRating;
  
  @override
  Widget build(BuildContext context) 
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: <Widget>[
        CartCounter(),
        Column(
            crossAxisAlignment: CrossAxisAlignment.center,
            mainAxisSize: MainAxisSize.max,
            children:
            <Widget>[
              SizedBox(
                height: 10.0,
              ),
              _ratingBar(_ratingBarMode),
              SizedBox(height: 5.0),
              Text(
                'Rating: $_rating',
                style: TextStyle(fontWeight: FontWeight.bold),
              ),
            ]
        ),
      ],
    );
  

  Widget _ratingBar(int mode) 
    return RatingBar.builder(
      initialRating: _initialRating,
      minRating: 1,
      direction: Axis.horizontal,
      allowHalfRating: true,
      unratedColor: Colors.amber.withAlpha(50),
      itemCount: 5,
      itemSize: 25.0,
      itemPadding: EdgeInsets.symmetric(horizontal: 2.0),
      itemBuilder: (context, _) => Icon(
        _selectedIcon ?? Icons.star,
        color: Colors.amber,
      ),
      onRatingUpdate: (rating) 
        setState(() 
          _rating = rating;
        );
      ,
      updateOnDrag: true,
    );
  

【参考方案1】：

你在 buildOutlineButtonDefinition 中有一个小错误

你立即调用 press 函数而不是使用 is 作为回调；

来自

onPressed: press(),

到

onPressed: () => press(),

完整的定义是

SizedBox buildOutlineButton(
      required IconData icon, required Function press) 
    return SizedBox(
      width: 40,
      height: 32,
      child: OutlinedButton(
        style: OutlinedButton.styleFrom(
          padding: EdgeInsets.zero,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(13.0)),
        ),
        onPressed: () => press(),
        child: Icon(icon),
      ),
    );