购物车计数器按下时没有更新值，没有显示错误

Question

我的应用程序中有一个购物车计数器的小代码，当运行应用程序时，它不会在按下添加或删除按钮(+&-图标(时更新，尽管我为它们分配了功能，但没有显示任何错误，说明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),
),
);
}
}

这是我称之为Cart Counter类的代码，它还有一个运行良好的评级栏：

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,
);
}
}

Answer 1

您在buildOutlineButtonDefinition 中有一个小错误

您立即调用press函数，而不使用is作为回调；

来自

onPressed: press(),

至

onPressed: () => press(),

完整定义为

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),
),
);
}