Incremental adding element to a SectionModel cause duplicate item issue

[ZZHHAANNGG]

I have a one section array. Whenever the user scrolls up the tableview, it loads the additional prefetched data from an API and adds the identical data to the end of the AnimatableSectionModelType Item. The section header is always an empty string. It crashes because there is a duplicate item at Indexpath(0,0).

Item CustomerJSON(UserId: Optional("016f0166-ead2-4719-88be-3f3bc45677c1"), UserName: Optional("13923715796"), CreateTime: Optional("2017/6/8 23:38:53"), GoodsCount: Optional(0), GoodsPrice: Optional(0.0)) has already been indexed at (0, 0)

What do I miss?

struct SectionOfCustomerJSON {
    var header: String
    var items: [Item]
}

extension SectionOfCustomerJSON: AnimatableSectionModelType {
    typealias Item = CustomerJSON
    
    var identity:String{
        return header
    }
    
    init(original: SectionOfCustomerJSON, items: [Item]) {
        self = original
        self.items = items
    }
}

let customerList = BehaviorRelay(value: Array<SectionOfCustomerJSON>())


/// add new elements logic
// previous array elements
let existedArray = self.customerList.value.last?.items ?? []

// new elements from the API
let newCustomerList:[CustomerJSON] = existedArray + customerList

// merge the array and create a new SectionModel instance
self.customerList.accept( [SectionOfCustomerJSON(header: "", items: newCustomerList)] )

The data looks this

OLD ARRAY:

[app.SectionOfCustomerJSON(header: "",
 items: [app.CustomerJSON(UserId: "016f0166-ead2-4719-88be-3f3bc45677c1,
 UserName: "13923715796,
 CreateTime: "2017/6/8 23:38:53,
 GoodsCount: 0),
 GoodsPrice: 0.0)),
 GoodsPrice: 13.0)),
 app.CustomerJSON(UserId: "7eba35d2-8f5c-405a-9e60-faf7559071c7,
 UserName: "13126887332,
 CreateTime: "2018/1/25 10:31:14,
 GoodsCount: 1),
 GoodsPrice: 18.0))])]


NEW ARRAY:

 [app.SectionOfCustomerJSON(header: "",
 items: [app.CustomerJSON(UserId: "016f0166-ead2-4719-88be-3f3bc45677c1,
 UserName: "13923715796,
 CreateTime: "2017/6/8 23:38:53,
 GoodsCount: 0),
 GoodsPrice: 0.0)),
 app.CustomerJSON(UserId: "7eba35d2-8f5c-405a-9e60-faf7559071c7,
 UserName: "13126887332,
 CreateTime: "2018/1/25 10:31:14,
 GoodsCount: 1),
 GoodsPrice: 18.0)),
 app.CustomerJSON(UserId: "00e0908c-0b08-403b-b72a-a199955054c8,
 UserName: "18112709797,
 CreateTime: "2017/8/19 14:01:06,
 GoodsCount: 26),
 GoodsPrice: 340.0))])]

[mkko]

What is a CustomerJSON? Is there a possibility that its identity is not unique?

[newPrimitives]

I have the same problem, almost identical code @ZZHHAANNGG did you manage to figure it out?

[460565420]

i have the same question, where can i set a different id ?

[buithuyen]

I have the same one.

[dfmarulanda]

Same

[mkko]

@ZZHHAANNGG, Can you paste the implementation details for CustomerJSON here? How does its implementation of IdentifiableType look like?

Anyone who's having issues, there's definitely a reason why the Differentiator thinks the item has been added and it is most likely to do with the item's identity. It has to be unique for each item.

[dfmarulanda]

import RxCocoa
import RxSwift
import RxKingfisher
import Differentiator

struct ItemExploreCellViewModel {
  let username: Driver<String>
  let userPic: Observable<URL?>
  let title: Driver<String>
  let description: Driver<String>
  let wishedCount: Driver<String>
  let imageURL: Driver<[String?]>
  let isWanted: Driver<Bool>
  let itemId: Int
  let isOwner: Driver<Bool>
  
  let item: ItemInfo
  init (item: ItemInfo, userId: Int) {
    self.item = item
    self.itemId = item.id
    self.username = Driver.just(item.swapperByOwnerId?.username ?? "")
    self.userPic = Observable.just(item.swapperByOwnerId?.profilePicture ?? "https://images.crowdswap.com/octavio.png").map { URL(string: $0) }
    self.title = Driver.just(item.name ?? "")
    self.description = Driver.just(item.description ?? "")
    self.wishedCount = Driver.just(item.countWants ?? "")
    self.imageURL = Driver.just(item.pictures ?? ["https://i0.wp.com/oij.org/wp-content/uploads/2016/05/placeholder.png"])
    self.isWanted = Driver.just(item.isWanted ?? false)
    self.isOwner = Driver.just(item.swapperByOwnerId?.id == userId)
  }
}

extension ItemExploreCellViewModel: IdentifiableType {
  typealias Identity = Int
  var identity: Int {
    return item.id
  }
}

extension ItemExploreCellViewModel: Equatable {
  static func == (lhs: ItemExploreCellViewModel, rhs: ItemExploreCellViewModel) -> Bool {
    return lhs.item.id == rhs.item.id  &&
      lhs.item.name == rhs.item.name &&
      lhs.item.description == rhs.item.description &&
      lhs.item.countWants == rhs.item.countWants &&
      lhs.item.pictures == rhs.item.pictures
  }
}

[dfmarulanda]

Did you find a workaround?