product_list_screen.dart

import 'package:flutter/material.dart';

import '../blocs/cart_bloc.dart';
import '../models/cart.dart';

class ProductListScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("eCommerce"),
        actions: [
          IconButton(
            icon: Icon(Icons.shopping_cart),
            onPressed: () => Navigator.pushNamed(context, "/cart"),
          )
        ],
      ),
      body: buildProductList(),
    );
  }

  buildProductList() {
    return StreamBuilder(
      initialData: productBloc.getAll(),
      stream: productBloc.getStream,
      builder: (context, snapshot) {
        return snapshot.data.length > 0 //error
            ? buildProductListItems(snapshot)
            : Center(
                child: Text("No data"),
              );
      },
    );
  }

  buildProductListItems(AsyncSnapshot<Object?> snapshot) {
    return ListView.builder(
        itemCount: snapshot.data.length, //error
        itemBuilder: (BuildContext context, index) {
          var list = snapshot.data;
          return ListTile(
            title: Text(list[index].name), //error
            subtitle: Text(list[index].price.toString()), //error
            trailing: IconButton(
              icon: Icon(Icons.add_shopping_cart),
              onPressed: () {
                cartBloc.addToCart(Cart(List[index], 1)); //error
              },
            ),
          );
        });
  }
}

The property 'length' can't be unconditionally accessed because the receiver can be 'null'. (Documentation) Try making the access conditional (using '?.') or adding a null check to the target ('!').

I used '!' or '?' but its didn't work. Can you help me? Thanks.

CodePudding user response：

You can try using null aware operator :

snapshot.data?.length ?? 0

CodePudding user response：

Do not use StreamBuilder use FutureBuilder Example:

FutureBuilder<Object?>(
    future: _fetchNetworkCall, // async work
    builder: (BuildContext context, AsyncSnapshot<Object?>snapshot) {
       switch (snapshot.connectionState) {
         case ConnectionState.waiting: return Text('Loading....');
         default:
           if (snapshot.hasError)
              return Text('Error: ${snapshot.error}');
           else
          return Text('Result: ${snapshot.data}');
        }
      },
    )