Update of @Published array does not update view

Seems to be one of the known issues of the current implementation of SwiftUI.

You may need to tell SwiftUI update views when `pictureController.images` has changed.

Though I cannot write any examples, as you have not shown enough code.

Thanks, I have also tried to extend the images array with this method:

var willChange = PassthroughSubject<Void, Never>()

@Published var images:[Picture] = []{
  willSet{
  willChange.send()
  }
  }

to make sure that a notification is sent but that also did not work.

Max

that also did not work.

So, I expect. It is not the right way under the current implementation of SwiftUI.

Can you maybe point me in a correct direction? 🙂

you have not shown enough code.

And code you shall get ... 🙂

• View
• Controller
• Picture class

import SwiftUI

struct PictureGalleryDemo: View {

  @ObservedObject private var pictureController: PictureController = PictureController()

    var body: some View {
  List(pictureController.images){ item in
  Text(item.bkey)
  }.onAppear{
  self.pictureController.fetchPicturesByTask(bkey_issue: "XYZ", completionHandler: { success in
  print(success)
  })
  }
    }
}

//
//

import Alamofire
import Combine
import Foundation
import SwiftUI
import SWXMLHash

final class PictureController: ObservableObject {
  var bkey_issue: String!
  var bkey: String!
  var statusMessage = ""
  var reference = ""
  var referenceType = ""
  var subProcess = ""
  var mode = ""
  var picture: Picture! = Picture()

  @Published var images: [Picture] = []

  var imageBuffer: [Picture] = []

  @Published var isLoading: Bool = false {
  willSet {
  self.willChange.send()
  }
  }

  @Published var statusCode: Int = 0 {
  willSet {
  willChange.send()
  }
  }

  @Published var loadError: Bool = false {
  willSet {
  self.willChange.send()
  }
  }

  var willChange = PassthroughSubject<Void, Never>()

  private let userSettings = UserSettings()

  init() {}

  public func fetchPicturesByTask(bkey_issue: String, completionHandler: @escaping (Bool) -> Void) {
  self.referenceType = ""
  self.reference = ""
  self.subProcess = "fetchPicturesByReference"
  self.bkey_issue = bkey_issue

  self.loadData(completionHandler: { success in
  if success {
  completionHandler(true)
  } else {
  completionHandler(false)
  }
  })
  }

  public func loadData(completionHandler: @escaping (Bool) -> Void) {
  let connectionPreCheck = ConnectionPreCheck()

  if !connectionPreCheck.validate() {
  self.statusMessage = connectionPreCheck.statusMessage
  self.loadError = true
  self.isLoading = false
  return
  }

  self.isLoading = true
  self.imageBuffer = []

  if self.bkey_issue == nil {
  self.bkey_issue = ""
  }

  let feedUrl = self.userSettings.host + ":\(self.userSettings.port!)/ws/kn-getOrderByClient-V1-VS/1.0/generic?userDomain=\(self.userSettings.userDomain!)&userID=\(self.userSettings.userID!)&token=\(self.userSettings.userToken!)&process=\(self.userSettings.process!)&subProcess=\(self.subProcess)&client=\(self.userSettings.client!)&depot=\(self.userSettings.depot!)&bkey_issue=\(self.bkey_issue!)&connection=\(self.userSettings.connectionKey!)"

  print(feedUrl)

  var request = URLRequest(url: URL(string: feedUrl)!)
  request.timeoutInterval = self.userSettings.timeout

  let urlSession = URLSession.shared
  let task = urlSession.dataTask(with: request, completionHandler: { (data, _, error) -> Void in
  guard let data = data else {
  if let error = error {
  // self.connectionErrorHandler(error: error as NSError)
  }
  return
  }

  let dataString = String(data: data, encoding: .utf8)
  // print(dataString)

  let xml = SWXMLHash.parse(dataString!)

  for elem in xml["DocumentXML"]["Message"]["Header"]["Pictures"]["Picture"].all {
  let item = Picture()
  item.bkey = elem["bkey"].element!.text
  item.imageType = elem["imageType"].element!.text
  self.imageBuffer.append(item)
  }

  DispatchQueue.main.async {
  self.images = self.imageBuffer
  completionHandler(true)
  }
  })

  task.resume()
  }
}

extension UIImage {
  func toBase64() -> String? {
  guard let imageData = self.pngData() else { return nil }
  return imageData.base64EncodedString(options: Data.Base64EncodingOptions.lineLength64Characters)
  }
}

import Foundation

class Picture: Codable, Identifiable, ObservableObject {

  var id = UUID()
  var bkey: String!
  var tmp_create: Date!
  var userDomain: String!
  var userID: String!
  var depot: String!
  var client: String!
  var process: String!
  var imageData: String!
  var imageType: String!
  var imageName: String!
  var reference: String!
  var referenceType: String!


  init() {

  }

}

Thanks for showing your code. But, sorry, it is not enough to check which workaround would fix the issue.

I needed to replace `loadData(completionHandler:)` with some dummy code, and the List in `PictureGalleryDemo` is updated as expected without any fixes.

I'm afraid `PictureGalleryDemo` is not the actual code causing the issue.

Ok, so I checked my actual complete code over and over again and the view where I called the PictureGallery from: turns out that that view had the variable

@Environment(\.presentationMode) var presentationMode

and once I commented that out, it works like a charme ...

I have no idea why that would make any difference ...

That may happen.

The reason I requested enough code, is that such subtle changes, which seem to be irrelevant to view updates, would change the behavior.

I do expect that SwiftUI 2, introduced in WWDC 2020 soon, would fix all such issues and we would not need any more do-not-know-why workarounds.

I have been debugging a similar issue (UI become out of sync) with my app, which involves no array. With additional debugging code, I found out that the SwiftUI attempts to update the UI when some values (in @ObservedObject) change, but the new value is not yet available at that time.

This is probably associated with a tricky update mechanism in SwiftUI, which uses Combine, which sends the notification before the value change.
https://developer.apple.com/forums/thread/128096

My code happened to have the following code and removing this line has solved this issue.

@Environment(\.presentationMode) var presentationMode

I faced a similar problem to the original issue.

I noticed,

• if you have any array of objects(class) : [ObjectA]
• as an @Published variable in a class: ClassA
• if you update any property of the objectA in the array [ObjectA], then the subscribers of @Published [ObjectA] will NOT trigger in ClassA

import Foundation
import Combine

class Object {
  var value: Int = 6

  init(value: Int) {
    self.value = value
  }
}

class MyClass {
  @Published var objects: [Object] = []
  var value: String = "Hello"
  var subscriptions = Set<AnyCancellable>()

  init(index: Int, value: String) {
    self.objects = [Object(value: index)]
    self.value = value

    $objects
      .sink {
        print($0.first?.value)
      }
      .store(in: &subscriptions)
  }
}


func changeMemberProperty(_ obj: MyClass) {
  if var first = obj.objects.first {
    print("Will change member property")
    first.value = Int.random(in: 100...400)
  }
  obj.value += "World"
}

var obj = MyClass(index: 1, value: "Hi")
changeMemberProperty(obj)
changeMemberProperty(obj)

func changeMember(_ obj: MyClass) {
  print("Will change member")
  obj.objects = [Object(value: Int.random(in: 100...400))]
}

changeMember(obj)
changeMember(obj)

Output:

Optional(1) /* Because of Print-command during initial setup */
Will change member property /* Didn't trigger Print-command */
Will change member property /* Didn't trigger Print-command */
Will change member
Optional(292) /* Due to triggered change: Print-command */
Will change member
Optional(259)  /* Due to triggered change: Print-command */