how to change ui inside a build ? flutter?

Issue

i am creating a app in which i need to show total price of the cart items: so i am getting data in json and returning that data in futurebuilder and accesing it like;

list[index]['price']

and intialize a variable for total :

double totalPrice = 0;

and adding values as follows:

FutureBuilder(
                future: myFuture,
builder: (context, AsyncSnapshot snapshot) {
if (!snapshot.hasData) {
// still waiting for data to come
return Center(
child: CircularProgressIndicator(),
);
} else if (snapshot.hasData &&
snapshot.data.isEmpty) {
return Center(child: Text("No Products"));
;
} else {
if (snapshot.hasError) print(snapshot.error);
return snapshot.hasData
? ListView.builder(

                   itemCount: snapshot.data!.length,
                    itemBuilder: (BuildContext context, index) {
  //below the code of adding price
  List list = snapshot.data;
  totalPrice = totalPrice + list[index]['price'];
    print("this is the total:$totalPrice");


                      return Container(..My Ui..
                ):Center(child: Text("no data"));
            }
            },  //futurebuilder ends here
                ), 
           Padding(
              padding: const EdgeInsets.all(16.0),
              child: Text(
                'Total :₹ $totalPrice',  // showing total price here
                style: TextStyle(
                    fontSize: 20,
                    color: darkGrey,
                    fontWeight: FontWeight.bold),
              ),
            ),
 

but this totalPrice always show 0

can someone tell me how to update this variable inside a build? Thanks in advance <3

Solution

Not try to do like this. Use these method..

FutureBuilder(builder: (context, snapshot) {
      if(snapshot.hasData){
        //Only run when you get data
        final list = snapshot.data;
        var totalPrice = list.map((e) => e[price]).toList()
            .reduce((value, element) => value + element);
    return ReturnYourWidget();
      }
      //Until you get data show the loader
      return Center(child: CircularProgressIndicator(),);
    },);

Answered By - Vishal_VE