无法共享CKRecord

Question

我写了下面的代码来共享一个CKRecord：

CKRecordZone *restaurantsZone = [[CKRecordZone alloc] initWithZoneName:@"RestaurantsZone"];
CKRecordID *recordID = [[CKRecordID alloc] initWithRecordName:self.recordName zoneID:restaurantsZone.zoneID];
CKRecord *record = [[CKRecord alloc] initWithRecordType:@"Restaurant" recordID:recordID];
[record setValue:self.restaurant forKey:@"name"];

UICloudSharingController *cloudSharingController = [[UICloudSharingController alloc] initWithPreparationHandler:^(UICloudSharingController * _Nonnull controller, void (^ _Nonnull preparationCompletionHandler)(CKShare * _Nullable, CKContainer * _Nullable, NSError * _Nullable)) {
    [self shareRootRecord:record name:self.restaurant completion:preparationCompletionHandler];
}];
cloudSharingController.delegate = self;
[self presentViewController:cloudSharingController animated:YES completion:nil];

和shareRootRecord函数：

- (void)shareRootRecord:(CKRecord *)rootRecord name:(NSString *)name completion:(void (^)(CKShare * _Nullable share, CKContainer * _Nullable container, NSError * _Nullable error))completion
{
    CKShare *shareRecord = [[CKShare alloc] initWithRootRecord:rootRecord];
    shareRecord[CKShareTitleKey] = name;
    NSArray *recordsToSave = @[rootRecord, shareRecord];
    CKContainer *container = [CKContainer defaultContainer];
    CKDatabase *privateDatabase = [container sharedCloudDatabase];

    CKModifyRecordsOperation *operation = [[CKModifyRecordsOperation alloc] initWithRecordsToSave:recordsToSave recordIDsToDelete:@[]];
    [operation setPerRecordCompletionBlock:^(CKRecord * _Nullable record, NSError * _Nullable error) {
        if (error) {
            NSLog(@"%@", [error localizedDescription]);
        }
    }];
    [operation setModifyRecordsCompletionBlock:^(NSArray<CKRecord *> * _Nullable savedRecords, NSArray<CKRecordID *> * _Nullable deletedRecordIDs, NSError * _Nullable error) {
        if (error) {
            NSLog(@"%@", [error localizedDescription]);
        }
        completion(shareRecord, container, error);
    }];

    [privateDatabase addOperation:operation];
}

现在，当我运行这段代码时，抛出了以下错误：Only shared zones can be accessed in the shared DB。不过，我似乎找不出原因。有什么想法吗？