购物车计数器在返回颤振时没有更新

Question

我正在购物车屏幕上将项目添加到购物车，但是当我返回产品以添加更多产品时，计数器没有在我的底部导航栏上更新，据我所知，该活动已经在堆栈中，因此它不刷新，我可以在本机android(java(的invalidateOptionMenu((函数上执行此操作，该函数刷新应用栏，但我不知道如何在 Flutter 中做到这一点，也不知道它的底部导航。

我已经在反压函数上尝试过这段代码

Navigator.of(context).push(
MaterialPageRoute(
builder: (BuildContext context){
return MainScreen();
},
),
);

在Willpopscope上， 任何帮助将不胜感激，下面是主屏幕

body: PageView(
physics: NeverScrollableScrollPhysics(),
controller: _pageController,
onPageChanged: onPageChanged,
children: <Widget>[
Home(),
FavoriteScreen(),
SearchScreen(),
CartScreen(),
Profile(),
],
),
bottomNavigationBar: BottomAppBar(
child: new Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
SizedBox(width:7),
IconButton(
icon: Icon(
Icons.home,
size: 24.0,
),
color: _page == 0
? Theme.of(context).accentColor
: Theme
.of(context)
.textTheme.caption.color,
onPressed: ()=>_pageController.jumpToPage(0),
),
IconButton(
icon:Icon(
Icons.favorite,
size: 24.0,
),
color: _page == 1
? Theme.of(context).accentColor
: Theme
.of(context)
.textTheme.caption.color,
onPressed: ()=>_pageController.jumpToPage(1),
),
IconButton(
icon: Icon(
Icons.search,
size: 24.0,
color: Theme.of(context).primaryColor,
),
color: _page == 2
? Theme.of(context).accentColor
: Theme
.of(context)
.textTheme.caption.color,
onPressed: ()=>_pageController.jumpToPage(2),
),
IconButton(
icon: IconBadge(
icon: Icons.shopping_cart,
size: 24.0,
),
color: _page == 3
? Theme.of(context).accentColor
: Theme
.of(context)
.textTheme.caption.color,
onPressed: ()=>_pageController.jumpToPage(3),
),
IconButton(
icon: Icon(
Icons.person,
size: 24.0,
),
color: _page == 4
? Theme.of(context).accentColor
: Theme
.of(context)
.textTheme.caption.color,
onPressed: ()=>_pageController.jumpToPage(4),
),
SizedBox(width:7),
],
),
color: Theme.of(context).primaryColor,
shape: CircularNotchedRectangle(),
),
floatingActionButtonAnimator: FloatingActionButtonAnimator.scaling,
floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
floatingActionButton: FloatingActionButton(
elevation: 4.0,
child: Icon(
Icons.search,
),
onPressed: ()=>_pageController.jumpToPage(2),
),
),
);

图标徽章

class IconBadge extends StatefulWidget {
final IconData icon;
final double size;
static int counteer;
IconBadge({Key key, @required this.icon, @required this.size})
: super(key: key);

@override
_IconBadgeState createState() => _IconBadgeState();
}
class _IconBadgeState extends State<IconBadge> {

//List _users;
static int count ; 
Future countForBadge() async{
var db = new DatabaseHelper();
count = await db.getCount();
print("Count: $count");
//print("khAN NNNN $counteer");
}
@override
void initState() {
// TODO: implement initState
super.initState();
countForBadge();
}

@override
Widget build(BuildContext context) {
if (count == null){
count = 0;
}
print("Count lande: $count");
return Stack(
children: <Widget>[
Icon(
widget.icon,
size: widget.size,
),
Positioned(
right: 0.0,
child: Container(
padding: EdgeInsets.all(1),
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(6),
),
constraints: BoxConstraints(
minWidth: 13,
minHeight: 13,
),
child: Padding(
padding: EdgeInsets.only(top: 1),
child:Text(
"$count",
style: TextStyle(
color: Colors.white,
fontSize: 8,
),
textAlign: TextAlign.center,
),
),
),
),
],
);
}
}

Answer 1

我已经用一个简单的Container()替换了一些屏幕。 如果我理解您的问题，这是使用VoidCallBack的解决方案：

主飞镖

import 'package:badges/badges.dart';
import 'package:flutter/material.dart';
import 'package:issue_counter_cart/cart_screen.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _page;
int _counter = 0;
PageController _pageController;
@override
void initState() {
super.initState();
_pageController = PageController();
}
@override
void dispose() {
_pageController.dispose();
super.dispose();
}
void _increaseCart() {
setState(() {
_counter++;
});
}
void _decreaseCart() {
setState(() {
_counter--;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: PageView(
physics: NeverScrollableScrollPhysics(),
controller: _pageController,
// onPageChanged: onPageChanged,
children: <Widget>[
Container(),
Container(),
Container(),
CartScreen(
increaseCart: () => _increaseCart(),
decreaseCart: () => _decreaseCart(),
),
Container(),
],
),
bottomNavigationBar: BottomAppBar(
child: new Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
SizedBox(width: 7),
IconButton(
icon: Icon(
Icons.home,
size: 24.0,
),
color: _page == 0
? Theme.of(context).accentColor
: Theme.of(context).textTheme.caption.color,
onPressed: () => _pageController.jumpToPage(0),
),
IconButton(
icon: Icon(
Icons.favorite,
size: 24.0,
),
color: _page == 1
? Theme.of(context).accentColor
: Theme.of(context).textTheme.caption.color,
onPressed: () => _pageController.jumpToPage(1),
),
IconButton(
icon: Icon(
Icons.search,
size: 24.0,
color: Theme.of(context).primaryColor,
),
color: _page == 2
? Theme.of(context).accentColor
: Theme.of(context).textTheme.caption.color,
onPressed: () => _pageController.jumpToPage(2),
),
IconButton(
icon: Badge(
badgeContent: Text(_counter.toString()),
child: Icon(Icons.shopping_cart),
),
color: _page == 3
? Theme.of(context).accentColor
: Theme.of(context).textTheme.caption.color,
onPressed: () => _pageController.jumpToPage(3),
),
IconButton(
icon: Icon(
Icons.person,
size: 24.0,
),
color: _page == 4
? Theme.of(context).accentColor
: Theme.of(context).textTheme.caption.color,
onPressed: () => _pageController.jumpToPage(4),
),
SizedBox(width: 7),
],
),
color: Theme.of(context).primaryColor,
shape: CircularNotchedRectangle(),
),
floatingActionButton: FloatingActionButton(
onPressed: () {},
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}

cart_screen.飞镖

import 'package:flutter/material.dart';
class CartScreen extends StatefulWidget {
final VoidCallback increaseCart;
final VoidCallback decreaseCart;
CartScreen({this.increaseCart, this.decreaseCart});
@override
_CartScreenState createState() => _CartScreenState();
}
class _CartScreenState extends State<CartScreen> {
@override
Widget build(BuildContext context) {
return Container(
child: Center(
child: Column(
children: <Widget>[
RaisedButton(
onPressed: widget.increaseCart,
child: Text('Increase cart'),
),
RaisedButton(
onPressed: widget.decreaseCart,
child: Text('Decrease cart'),
),
],
),
),
);
}
}

为了简化代码，我使用了 bagdes 包