【发布时间】：2022-01-17 22:01:10
【问题描述】：
我正在尝试通过按“处理订单”按钮导航到新屏幕，但我不断收到错误 [VERBOSE-2:ui_dart_state.cc(209)] 未处理的异常：空检查运算符用于空值。我不确定错误到底发生在哪里。
我已经为此苦苦挣扎了一段时间。这可能是什么问题？
class CartScreen extends StatefulWidget {
const CartScreen({
Key? key,
}) : super(key: key);
static const routeName = '/cart-screen';
@override
State<CartScreen> createState() => _CartScreenState();
}
class _CartScreenState extends State<CartScreen> {
final user = FirebaseAuth.instance.currentUser;
final TextEditingController deliveryNoteController = TextEditingController();
bool isLoading = false;
@override
Widget build(BuildContext context) {
final cart = Provider.of<Cart>(context);
return isLoading
? const LoadingSpinner()
: Scaffold(
appBar: AppBar(
automaticallyImplyLeading: false,
elevation: 0,
iconTheme: IconThemeData(color: Colors.blueGrey[900]),
title: const Text(
'Order Summary',
style: TextStyle(color: Colors.black),
),
),
body: cart.totalAmount <= 0
? const EmptyCartScreen()
: SingleChildScrollView(
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 15.0),
child: Column(
children: <Widget>[
StreamBuilder<DocumentSnapshot>(
stream: FirebaseFirestore.instance
.collection('users')
.doc(user!.uid)
.snapshots(),
builder: (context, snapshot) {
if (snapshot.hasError) {
return const Text(
'Oops, something went wrong.');
}
if (!snapshot.hasData) {
return const LoadingSpinner();
}
DocumentSnapshot? doc = snapshot.data;
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
ListView.builder(
physics:
const NeverScrollableScrollPhysics(),
shrinkWrap: true,
scrollDirection: Axis.vertical,
itemCount: cart.items.length,
itemBuilder: (context, i) => CartItem(
cart.items.values.toList()[i].id,
cart.items.keys.toList()[i],
cart.items.values.toList()[i].price,
cart.items.values.toList()[i].quantity,
cart.items.values
.toList()[i]
.title
.toString(),
),
),
Row(
children: [
const Text(
'Delivery Address',
style: TextStyle(
fontWeight: FontWeight.w600,
fontSize: 16.0,
),
),
const Spacer(),
TextButton(
child: const Text('Edit'),
onPressed: () {
showModalBottomSheet(
context: context,
builder: (context) =>
const Padding(
padding: EdgeInsets.symmetric(
horizontal: 20.0,
vertical: 30.0,
),
child: EditDeliveryInfoForm(),
),
);
},
),
],
),
Column(
children: [
ListTile(
horizontalTitleGap: 0.0,
visualDensity: const VisualDensity(
horizontal: 0, vertical: -4),
leading: const Icon(
Ionicons.location_outline),
title: Text(doc!['address']),
),
ListTile(
horizontalTitleGap: 0.0,
visualDensity: const VisualDensity(
horizontal: 0, vertical: -4),
leading: const Icon(
Ionicons.person_outline),
title: Text(doc['name']),
),
ListTile(
horizontalTitleGap: 0.0,
visualDensity: const VisualDensity(
horizontal: 0, vertical: -4),
leading:
const Icon(Ionicons.call_outline),
title: Text(doc['phoneNumber']),
),
const SizedBox(
height: 10.0,
),
TextField(
controller: deliveryNoteController,
decoration: InputDecoration(
hintText: 'Delivery note',
enabledBorder: OutlineInputBorder(
borderRadius:
BorderRadius.circular(8.0),
borderSide: BorderSide(
color: Colors.grey.shade400,
width: 1.6,
),
),
focusedBorder: OutlineInputBorder(
borderRadius:
BorderRadius.circular(8.0),
borderSide: BorderSide(
color: Colors
.lightBlueAccent.shade700,
width: 1.6,
),
),
),
),
const SizedBox(
height: 12.0,
),
],
),
const Divider(
thickness: 1.2,
),
Padding(
padding: const EdgeInsets.all(15.0),
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceBetween,
children: [
const Text(
'Total Due',
style: TextStyle(fontSize: 18),
),
Text(
'R${cart.totalAmount.toStringAsFixed(2)}',
style: const TextStyle(
fontSize: 22,
letterSpacing: 0.5,
fontWeight: FontWeight.bold),
),
],
),
),
ElevatedButton(
child: const Center(
child: Padding(
padding: EdgeInsets.symmetric(
vertical: 15.0),
child: Text(
'Process Order',
style: TextStyle(
color: Colors.white,
),
),
),
),
onPressed: () async {
try {
setState(() {
isLoading = true;
});
await FirebaseFirestore.instance
.collection('orders')
.add({
'date': DateTime.now(),
'order': cart.items.values
.map((prod) =>
'${prod.title}, ${prod.quantity}')
.join(";")
.toString(),
'total': cart.totalAmount
.toStringAsFixed(2),
});
Navigator.of(context)
.pushReplacementNamed(
OrderSuccess.routeName);
setState(() {
isLoading = false;
});
cart.clearCart();
} on FirebaseException catch (e) {
print(e.toString());
setState(() {
isLoading = false;
});
}
},
),
const SizedBox(
height: 20.0,
),
],
);
}),
],
),
),
),
);
}
}
【问题讨论】：
标签： flutter dart google-cloud-firestore dart-null-safety