Flutter: Updating UI from outside of a StatefulWidget - flutter

Question

I am new to flutter, and working on a shopping cart project. i don't know how exatly i am suppose to ask this question but, here is what i wanted.
I am trying to update my UI when the cart item and prices changes, which means to display sum amount of products from ListView (Stateful widget) to main OrderPage Stateful widget. I know about setState() method, but i think i should use some callback methods here, dont know exactly.
I have explained in short in Image - see below img
What i have done: when user modify cart products, I have saved the value (price/product/count) in to constant value , i calculate the value and save in constant value, and later use that const var in Main widget (Main Ui), which does update when i close and reopen the page, but could not able to update when button pressed (product +/-buttons)
What i want to do is,
Update my total value when +/- buttons are pressed.
Here is my full code:
class cartConstant{
static int packageCount;
static List<int> list;
}
class OrderPage extends StatefulWidget {
#override
_OrderPageState createState() => _OrderPageState();
}
class _OrderPageState extends State<OrderPage> {
int data = 3;
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
automaticallyImplyLeading: true,
iconTheme: IconThemeData(
color: Colors.black54, //change your color here
),
backgroundColor: Colors.white,
elevation: 1,
title: Text("Your order Summery",style: TextStyle(color: Colors.black54),),
centerTitle: true,
),
body: Container(
child:
FutureBuilder(
builder: (context, snapshot){
// var datas = snapshot.data;
return
ListView.builder(
physics: ClampingScrollPhysics(),
shrinkWrap: true,
itemCount: data,
itemBuilder: (BuildContext context, int index){
// Cart cart = datas[index];
return CartListView();
},
padding: EdgeInsets.symmetric(horizontal: 10.0),
scrollDirection: Axis.vertical,
);
},
),
),
bottomNavigationBar: _buildTotalContainer(),
);
}
Widget _buildTotalContainer() {
return Container(
height: 220.0,
padding: EdgeInsets.only(
left: 10.0,
right: 10.0,
),
child: Column(
children: <Widget>[
SizedBox(
height: 10.0,
),
Padding(
padding: const EdgeInsets.only(top: 10),
child: Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Subtotal",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
cartConstant.packageCount.toString(),
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
),
SizedBox(
height: 15,
),
Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Discount",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
"0.0",
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
SizedBox(
height: 10.0,
),
Divider(
height: 2.0,
),
SizedBox(
height: 20.0,
),
Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Cart Total",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
cartConstant.packageCount.toString(),
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
SizedBox(
height: 20.0,
),
GestureDetector(
onTap: () {
// Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) => SignInPage()));
},
child: Container(
height: 50.0,
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(35.0),
),
child: Center(
child: Text(
"Proceed To Checkout",
style: TextStyle(
color: Colors.white,
fontSize: 18.0,
fontWeight: FontWeight.bold,
),
),
),
),
),
SizedBox(
height: 20.0,
),
],
),
);
}
}
class CartListView extends StatefulWidget {
#override
_CartListViewState createState() => _CartListViewState();
}
class _CartListViewState extends State<CartListView> {
int _counter = 1;
int getPrice(int i,int priceC){
cartConstant.packageCount = i*priceC;
return cartConstant.packageCount;
}
#override
Widget build(BuildContext context) {
return Card(
child: Padding(
padding: EdgeInsets.symmetric(horizontal: 15.0, vertical: 15.0),
child: Row(
mainAxisSize: MainAxisSize.max,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Container(
decoration: BoxDecoration(
border: Border.all(color: Color(0xFFD3D3D3), width: 2.0),
borderRadius: BorderRadius.circular(10.0),
),
child: Padding(
padding: EdgeInsets.symmetric(
horizontal: 10.0,
),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
InkWell(
onTap: (){
setState(() {
_counter++;
if (_counter > 20) {
_counter = 20;
}
});
},
child: Icon(Icons.add, color: Color(0xFFD3D3D3))),
Text(
"$_counter",
style: TextStyle(fontSize: 18.0, color: Colors.grey),
),
InkWell(
onTap:(){
setState(() {
_counter--;
if (_counter < 2) {
_counter = 1;
}
});
},
child: Icon(Icons.remove, color: Color(0xFFD3D3D3))),
],
),
),
),
SizedBox(
width: 20.0,
),
Container(
height: 70.0,
width: 70.0,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage("assets/images/food.jpg"),
fit: BoxFit.cover),
borderRadius: BorderRadius.circular(35.0),
boxShadow: [
BoxShadow(
color: Colors.black54,
blurRadius: 5.0,
offset: Offset(0.0, 2.0))
]),
),
SizedBox(
width: 20.0,
),
Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
"Employee Package",
style: TextStyle(fontSize: 16.0, fontWeight: FontWeight.bold),
),
SizedBox(height: 5.0),
SizedBox(height: 5.0),
Container(
height: 25.0,
width: 120.0,
child: ListView(
scrollDirection: Axis.horizontal,
children: <Widget>[
Row(
children: <Widget>[
Text("Price",
style: TextStyle(
color: Color(0xFFD3D3D3),
fontWeight: FontWeight.bold)),
SizedBox(
width: 5.0,
),
InkWell(
onTap: () {},
child: Text(
getPrice(_counter, 2000).toString(),
style: TextStyle(
fontWeight: FontWeight.bold,
color: Colors.red,
),
),
),
SizedBox(
width: 10.0,
),
],
),
],
),
),
],
),
Spacer(),
GestureDetector(
onTap: () {
},
child: Icon(
Icons.cancel,
color: Colors.grey,
),
),
],
),
),
);
}
}
you can also check from my cart screen shot below:

Answer 1

You can copy paste run full code below
You can use callback refresh() and pass callback to CartListView
code snippet
class _OrderPageState extends State<OrderPage> {
int data = 3;
void refresh() {
setState(() {});
}
...
itemBuilder: (BuildContext context, int index) {
// Cart cart = datas[index];
return CartListView(refresh);
},
...
class CartListView extends StatefulWidget {
VoidCallback callback;
CartListView(this.callback);
...
InkWell(
onTap: () {
setState(() {
_counter++;
if (_counter > 20) {
_counter = 20;
}
});
widget.callback();
},
working demo
full code
import 'package:flutter/material.dart';
class cartConstant {
static int packageCount;
static List<int> list;
}
class OrderPage extends StatefulWidget {
#override
_OrderPageState createState() => _OrderPageState();
}
class _OrderPageState extends State<OrderPage> {
int data = 3;
void refresh() {
setState(() {});
}
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Colors.white,
appBar: AppBar(
automaticallyImplyLeading: true,
iconTheme: IconThemeData(
color: Colors.black54, //change your color here
),
backgroundColor: Colors.white,
elevation: 1,
title: Text(
"Your order Summery",
style: TextStyle(color: Colors.black54),
),
centerTitle: true,
),
body: Container(
child: FutureBuilder(
builder: (context, snapshot) {
// var datas = snapshot.data;
return ListView.builder(
physics: ClampingScrollPhysics(),
shrinkWrap: true,
itemCount: data,
itemBuilder: (BuildContext context, int index) {
// Cart cart = datas[index];
return CartListView(refresh);
},
padding: EdgeInsets.symmetric(horizontal: 10.0),
scrollDirection: Axis.vertical,
);
},
),
),
bottomNavigationBar: _buildTotalContainer(),
);
}
Widget _buildTotalContainer() {
return Container(
height: 220.0,
padding: EdgeInsets.only(
left: 10.0,
right: 10.0,
),
child: Column(
children: <Widget>[
SizedBox(
height: 10.0,
),
Padding(
padding: const EdgeInsets.only(top: 10),
child: Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Subtotal",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
cartConstant.packageCount.toString(),
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
),
SizedBox(
height: 15,
),
Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Discount",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
"0.0",
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
SizedBox(
height: 10.0,
),
Divider(
height: 2.0,
),
SizedBox(
height: 20.0,
),
Row(
mainAxisSize: MainAxisSize.max,
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
"Cart Total",
style: TextStyle(
color: Color(0xFF9BA7C6),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
Text(
"8000",
style: TextStyle(
color: Color(0xFF6C6D6D),
fontSize: 16.0,
fontWeight: FontWeight.bold),
),
],
),
SizedBox(
height: 20.0,
),
GestureDetector(
onTap: () {
// Navigator.of(context).push(MaterialPageRoute(builder: (BuildContext context) => SignInPage()));
},
child: Container(
height: 50.0,
decoration: BoxDecoration(
color: Colors.red,
borderRadius: BorderRadius.circular(35.0),
),
child: Center(
child: Text(
"Proceed To Checkout",
style: TextStyle(
color: Colors.white,
fontSize: 18.0,
fontWeight: FontWeight.bold,
),
),
),
),
),
SizedBox(
height: 20.0,
),
],
),
);
}
}
class CartListView extends StatefulWidget {
VoidCallback callback;
CartListView(this.callback);
#override
_CartListViewState createState() => _CartListViewState();
}
class _CartListViewState extends State<CartListView> {
int _counter = 1;
int getPrice(int i, int priceC) {
cartConstant.packageCount = i * priceC;
return cartConstant.packageCount;
}
#override
Widget build(BuildContext context) {
return Card(
child: Padding(
padding: EdgeInsets.symmetric(horizontal: 15.0, vertical: 15.0),
child: Row(
mainAxisSize: MainAxisSize.max,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Container(
decoration: BoxDecoration(
border: Border.all(color: Color(0xFFD3D3D3), width: 2.0),
borderRadius: BorderRadius.circular(10.0),
),
child: Padding(
padding: EdgeInsets.symmetric(
horizontal: 10.0,
),
child: Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
InkWell(
onTap: () {
setState(() {
_counter++;
if (_counter > 20) {
_counter = 20;
}
});
widget.callback();
},
child: Icon(Icons.add, color: Color(0xFFD3D3D3))),
Text(
"$_counter",
style: TextStyle(fontSize: 18.0, color: Colors.grey),
),
InkWell(
onTap: () {
setState(() {
_counter--;
if (_counter < 2) {
_counter = 1;
}
});
widget.callback();
},
child: Icon(Icons.remove, color: Color(0xFFD3D3D3))),
],
),
),
),
SizedBox(
width: 20.0,
),
Container(
height: 70.0,
width: 70.0,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage("assets/images/food.jpg"),
fit: BoxFit.cover),
borderRadius: BorderRadius.circular(35.0),
boxShadow: [
BoxShadow(
color: Colors.black54,
blurRadius: 5.0,
offset: Offset(0.0, 2.0))
]),
),
SizedBox(
width: 20.0,
),
Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
"Employee Package",
style: TextStyle(fontSize: 16.0, fontWeight: FontWeight.bold),
),
SizedBox(height: 5.0),
SizedBox(height: 5.0),
Container(
height: 25.0,
width: 120.0,
child: ListView(
scrollDirection: Axis.horizontal,
children: <Widget>[
Row(
children: <Widget>[
Text("Price",
style: TextStyle(
color: Color(0xFFD3D3D3),
fontWeight: FontWeight.bold)),
SizedBox(
width: 5.0,
),
InkWell(
onTap: () {},
child: Text(
getPrice(_counter, 2000).toString(),
style: TextStyle(
fontWeight: FontWeight.bold,
color: Colors.red,
),
),
),
SizedBox(
width: 10.0,
),
],
),
],
),
),
],
),
Spacer(),
GestureDetector(
onTap: () {},
child: Icon(
Icons.cancel,
color: Colors.grey,
),
),
],
),
),
);
}
}
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: OrderPage(),
);
}
}

Answer 2

When the button is tapped, you just need to update the Subtotal amount and cart total.
Step 1 : Replace the harcoded value by a variable. So, something like :
Row(
children: <Widget>[
Text(
"Subtotal",
style: ...
),
Text(
"$subTotal",
style: ....
),
],
),
Step 2 : Now, add a code to calcualte subTotal and cartTotal. You already have code which increments and decrements the variable _counter. You just need to tweak that part like :
setState( (){
_counter++;
// So, the quantity is increased. Just get the price of current item and add in the sub total.
subTotal += priceC;
cartTotal = subTotal - discount;
} );