Flutter riverpod使用通知程序递增状态

Question

在以前版本的Riverpod中，我可以很容易地通过copyWith来增加状态中的一些数据，但在该库的riverpod: ^1.0.3版本中，我无法做到这一点。例如：

/* click event to increment */
ref.read(orderStructureProvider.notifier).increment(breadId: id);

order通知程序：

final orderStructureProvider = StateNotifierProvider<OrderNotifier, OrderStructure>((ref) => OrderNotifier());
class OrderNotifier extends StateNotifier<OrderStructure> {
OrderNotifier() : super(_initial);
static const OrderStructure _initial = OrderStructure(
address: Address(
address: 'address',
province: {},
city: {},
neighbourhood: {},
),
breads: [],
baker: [],
paymentType: 1,
);
void resetOrder() => state = _initial;
int breadsCount() => state.breads.length;
void updateAddress(
String _address,
Map<String, dynamic> _province,
Map<String, dynamic> _city,
Map<String, dynamic> _neighbourhood,
) {
state = OrderStructure(
address: Address(
address: _address,
province: _province,
city: _city,
neighbourhood: _neighbourhood,
),
breads: [...state.breads],
baker: [],
paymentType: state.paymentType,
);
}
BreadStructure? getService(int breadId) {
final index = state.breads.indexWhere((bread) => bread.id == breadId);
return index >= 0 ? state.breads[index] : null;
}
void create(BreadStructure _bread) {
final newState = OrderStructure(
address: state.address,
breads: [...state.breads, _bread],
baker: [...state.baker],
paymentType: state.paymentType,
);
//newState.breads=[...state.breads,_bread];
state = newState;
}
bool breadExists(int breadId) => state.breads.indexWhere((bread) => bread.id == breadId) == -1;
void increment({required int breadId}) {
final newState = OrderStructure(
address: state.address,
breads: [...state.breads],
baker: [...state.baker],
paymentType: state.paymentType,
);
debugPrint(state.breads.toString());
final int index = newState.breads.indexWhere((element) => element.id == breadId);
newState.breads[index].copyWith(count: 44);
//debugPrint(newState.breads.toString());
state = newState;
}
void decrement(int breadId) {
final newState = OrderStructure(
address: state.address,
breads: [...state.breads],
baker: [...state.baker],
paymentType: state.paymentType,
);
final index = state.breads.indexWhere((element) => element.id == breadId);
BreadStructure bread = newState.breads[index];
if (index >= 0) {
if (bread.count <= 1) {
newState.breads.removeAt(index);
} else {
bread = bread.copyWith(count: bread.count - 1);
}
}
state = newState;
}
}
@freezed
abstract class OrderStructure with _$OrderStructure {
const factory OrderStructure({
required Address address,
required List<BreadStructure> breads,
required List<Map<String, dynamic>> baker,
required int paymentType,
}) = _OrderStructure;
factory OrderStructure.fromJson(Map<String, dynamic> json) => _$OrderStructureFromJson(json);
}
@freezed
abstract class Address with _$Address {
const factory Address({
required String address,
required Map<String, dynamic> province,
required Map<String, dynamic> city,
required Map<String, dynamic> neighbourhood,
}) = _Address;
factory Address.fromJson(Map<String, dynamic> json) => _$AddressFromJson(json);
}
@freezed
abstract class BreadStructure with _$BreadStructure {
const factory BreadStructure({
required int id,
required String name,
required int count,
}) = _BreadStructure;
factory BreadStructure.fromJson(Map<String, dynamic> json) => _$BreadStructureFromJson(json);
}

输出：

0
1
1
1
1
1
...

Answer 1

问题是

newState.breads[index].copyWith(count: 44);

copyWith()正在返回参数已修改的新实例，而不是编辑当前实例。

解决方案

void increment({required int breadId}) {
final int index = state.breads.indexWhere((bread) => bread.id == breadId);
final bread = state.breads[index];
final updatedBread = bread.copyWith(count: bread.count + 1);

/* save to state */
state = state.copyWith(
breads: List.from(state.breads)..[index] = updatedBread,
);
}