how to use widget value from stateful into stateless - flutter

Question

I am having a stuck on transferring the value from the second page to the third page using the value pass from the first page. when I am trying to use the usual way that I am used to calling the data in the stateful widget, it returns an error on undefined.
class restaurantLISTVIEW extends StatefulWidget {
restaurantLISTVIEW({this.category});
final String category;
#override
_restaurantLISTVIEWState createState() => _restaurantLISTVIEWState();
}
within extends state:(working)
FloatingActionButton(
onPressed: (){
return showDialog(
context: context,
builder: (context){
return AlertDialog(
content: Text(
'${widget.category}'
),
);
},
);
},),
error on extends stateless widget, return null: (not working)
onTap: ()
{
Navigator.of(context).push(new MaterialPageRoute(builder: (BuildContext context)=> new SarapanPagi(list: list, index: i, category: category)));
}
within extends stateless:(not working)
FloatingActionButton(
onPressed: (){
return showDialog(
context: context,
builder: (context){
return AlertDialog(
content: Text(
'$category hellp'
),
);
},
);
},),
The whole code on the second page:
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'package:http/http.dart' as HTTP;
import 'breakfast.dart';
// ignore: camel_case_types
class restaurantLISTVIEW extends StatefulWidget {
restaurantLISTVIEW({this.category});
final String category;
#override
_restaurantLISTVIEWState createState() => _restaurantLISTVIEWState();
}
// ignore: camel_case_types
class _restaurantLISTVIEWState extends State<restaurantLISTVIEW> {
Future<List> getData() async{
var url = 'http://10.0.2.2/foodsystem/restaurantlist.php';
var data = {'product_type': 'xde pape ppon saje nk hantar value'};
var response = await http.post(url, body: json.encode(data));
//final response= await http.get("http://10.0.2.2/foodsystem/getdata.php");
return json.decode(response.body);}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
iconTheme: IconThemeData(color: Colors.black),
title: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
//Text("Restaurant's Owner Page"),
Text('${widget.category}', textAlign: TextAlign.center, style: TextStyle(fontSize: 25, fontWeight: FontWeight.w700), ),
],
),
centerTitle: false,
//automaticallyImplyLeading: false,
),
body:
Padding(
padding: const EdgeInsets.only(bottom: 20, left: 5, right: 5),
child: Column(
children: [
SizedBox(height: 30,),
Container(
//decoration: BoxDecoration(border: Border.all(color: Colors.black, width: 4), borderRadius: BorderRadius.circular(15)),
height: 600,
child: FutureBuilder<List>(
future: getData(),
builder: (context, snapshot){
if(snapshot.hasError) print(snapshot.error);
return snapshot.hasData ?
ItemList(list: snapshot.data,) :
Center(child: CircularProgressIndicator(),);
},
),
),
FloatingActionButton(
onPressed: (){
return showDialog(
context: context,
builder: (context){
return AlertDialog(
content: Text(
'${widget.category}'
),
);
},
);
},
),
SizedBox(height: 10,),
],
),
),
);
}
}
class ItemList extends StatelessWidget {
final List list;
final String category;
ItemList({this.list, this.category});
#override
Widget build(BuildContext context) {
return SingleChildScrollView(
child: Container(
//color: Colors.red.shade100,
height: 600,
child: ListView.builder(
itemCount: list==null ? 0 : list.length,
itemBuilder: (context, i){
return new Container(
height: 200,
child: new GestureDetector(
onTap: ()
{
if(widget.category == "Breakfast"){
Navigator.of(context).push(new MaterialPageRoute(builder: (BuildContext context)=> new SarapanPagi(list: list, index: i, category: category)));
}
},
child: new Card(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
children: [
Container(
constraints: BoxConstraints(minWidth: 180, maxWidth: 180),
child:
Column(
children: [
Text(list[i]["restaurant_name"], style: TextStyle(fontSize: 25, fontWeight: FontWeight.bold), textAlign: TextAlign.center,),
Text("Restaurant ID: ${list[i]["restaurant_id"]}", style: TextStyle(fontSize: 20,), textAlign: TextAlign.center,),
],
),
),
Padding(
padding: const EdgeInsets.only(left :20.0),
child: Container(
constraints: BoxConstraints(minWidth: 150, maxWidth: 300),
child:
SizedBox(
width: 50,
child: Column(
children: [
Text("SSM: ${list[i]["restaurant_ssm"]}", textAlign: TextAlign.center, style: TextStyle(fontSize: 15),),
Text("Phone: ${list[i]["restaurant_phone"]}", textAlign: TextAlign.center, style: TextStyle(fontSize: 15),),
Text("Address: ${list[i]["restaurant_address"]}", textAlign: TextAlign.center, style: TextStyle(fontSize: 15),),
],
),
),
),
),
],
),
Row(
children: [
],
),
],
),
),
),
);
},
),
),
);
The whole code on the third page:
import 'dart:convert';
import 'package:http/http.dart' as HTTP;
import 'package:flutter/material.dart';
//import 'globals.dart' as globals;
class SarapanPagi extends StatefulWidget {
final List list;
final int index;
final String category;
SarapanPagi({this.index,this.list,this.category});
#override
_SarapanPagiState createState() => _SarapanPagiState();
}
class _SarapanPagiState extends State<SarapanPagi> {
Future<List> getData() async{
var url = 'http://10.0.2.2/foodsystem/breakfastlist.php';
var data = {
'product_type': 'Breakfast',
'product_owner': widget.list[widget.index]['restaurant_id'],
};
var response = await http.post(url, body: json.encode(data));
//final response= await http.get("http://10.0.2.2/foodsystem/getdata.php");
return json.decode(response.body);}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
iconTheme: IconThemeData(color: Colors.black),
title: Row(
mainAxisAlignment: MainAxisAlignment.start,
children: [
//Text("Restaurant's Owner Page"),
Text(widget.list[widget.index]['restaurant_name'], textAlign: TextAlign.center, style: TextStyle(fontWeight: FontWeight.w700), ),
],
),
centerTitle: false,
//automaticallyImplyLeading: false,
),
body:
Padding(
padding: const EdgeInsets.only(bottom: 20, left: 5, right: 5),
child: Column(
children: [
SizedBox(height: 30,),
Container(
//decoration: BoxDecoration(border: Border.all(color: Colors.black, width: 4), borderRadius: BorderRadius.circular(15)),
height: 600,
child: FutureBuilder<List>(
future: getData(),
builder: (context, snapshot){
if(snapshot.hasError) print(snapshot.error);
return snapshot.hasData ?
ItemList(list: snapshot.data,) :
Center(child: CircularProgressIndicator(),);
},
),
),
SizedBox(height: 10,),
],
),
),
);
}
}
class ItemList extends StatelessWidget {
final List list;
ItemList({this.list});
#override
Widget build(BuildContext context) {
return SingleChildScrollView(
child: Container(
//color: Colors.red.shade100,
height: 600,
child: ListView.builder(
itemCount: list==null ? 0 : list.length,
itemBuilder: (context, i){
return new Container(
height: 200,
child: new GestureDetector(
onTap: (){},
child: new Card(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: Image.asset(
"images/${list[i]['image']}",
width: 150,
height: 150,
),
),
Padding(
padding: const EdgeInsets.only(left: 20.0, bottom: 0),
child:
Column(
children: [
Text(list[i]["product_name"], textAlign: TextAlign.center, style: TextStyle(fontSize: 30),),
Text("Price RM : ${list[i]["product_price"]}", textAlign: TextAlign.center, style: TextStyle(fontSize: 25),),
RaisedButton(
shape: RoundedRectangleBorder(borderRadius: new BorderRadius.circular(40.0)),
color: Colors.red.shade300,
child: Text("Add to Cart", style: TextStyle(fontWeight: FontWeight.bold),),
onPressed: (){},
)
],
),
),
],
),
/*ListTile(
title: Text(list[i]["product_name"], textAlign: TextAlign.center, style: TextStyle(fontSize: 30),),
leading:
Image.asset(
"images/${list[i]['image']}",
width: 100,
height: 100,
),
subtitle: Text("Price RM : ${list[i]["product_price"]}", textAlign: TextAlign.center, style: TextStyle(fontSize: 25),),
),*/
],
),
),
),
);
},
),
),
);
The

Answer 1

You are not using widget.category in restaurantLISTVIEW page but in ItemList widget, that's why you are getting that error.
Adjust your ItemList widget like this
class ItemList extends StatelessWidget {
final List list;
final String category;
ItemList({this.list, this.category});
}
So, your navigation line in ItemList must be
Navigator.of(context).push(new MaterialPageRoute(builder: (BuildContext context)=> new SarapanPagi(list: list, index: i, category: category)));
Also, in SarapanPagi page the variable type of category is not int by String

Answer 2

You are not using widget.category in restaurantLISTVIEW page but in ItemList widget,

Answer 3

The solution that I made is:
this code on the stateful widget class for the second page, needs to be improved by adding the value of the category.
ItemList(list: snapshot.data,)
improved code:
this code forwards the value store in the widget category to the second page from the stateful widget into stateless widget.
ItemList(list: snapshot.data,category: widget.category) :