Build apps that share data through CloudKit and Core Data

5:20 - Add shared store description

let privateStoreDescription = container.persistentStoreDescriptions.first!
let storesURL = privateStoreDescription.url!.deletingLastPathComponent()
privateStoreDescription.url = storesURL.appendingPathComponent("private.sqlite")
privateStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
privateStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)

let sharedStoreURL = storesURL.appendingPathComponent("shared.sqlite")
let sharedStoreDescription = privateStoreDescription.copy()
sharedStoreDescription.url = sharedStoreURL

let containerIdentifier = privateStoreDescription.cloudKitContainerOptions!.containerIdentifier
let sharedStoreOptions = NSPersistentCloudKitContainerOptions(containerIdentifier: containerIdentifier)
sharedStoreOptions.databaseScope = .shared
sharedStoreDescription.cloudKitContainerOptions = sharedStoreOptions
container.persistentStoreDescriptions.append(sharedStoreDescription)

6:00 - shareNoteAction, DetailViewController.swift

@IBAction func shareNoteAction(_ sender: Any) {
  guard let barButtonItem = sender as? UIBarButtonItem else {
    fatalError("Not a UI Bar Button item??")
  }

  guard let post = self.post else {
    fatalError("Can't share without a post")
  }

  let container = AppDelegate.sharedAppDelegate.coreDataStack.persistentContainer
  let cloudSharingController = UICloudSharingController {
    (controller, completion: @escaping (CKShare?, CKContainer?, Error?) -> Void) in
    container.share([post], to: nil) { objectIDs, share, container, error in
			if let actualShare = share {
				post.managedObjectContext?.performAndWait {
					actualShare[CKShare.SystemFieldKey.title] = post.title
				}
			}
			completion(share, container, error)
		}
  }
  cloudSharingController.delegate = self

  if let popover = cloudSharingController.popoverPresentationController {
    popover.barButtonItem = barButtonItem
  }
  present(cloudSharingController, animated: true) {}
}

17:06 - SharingProvider

protocol SharingProvider {
  func isShared(object: NSManagedObject) -> Bool
  func isShared(objectID: NSManagedObjectID) -> Bool
  func participants(for object: NSManagedObject) -> [RenderableShareParticipant]
  func shares(matching objectIDs: [NSManagedObjectID]) throws -> [NSManagedObjectID: RenderableShare]
  func canEdit(object: NSManagedObject) -> Bool
  func canDelete(object: NSManagedObject) -> Bool
}

17:58 - Decorate table cells for shared posts, MainViewController.swift

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    guard let cell = tableView.dequeueReusableCell(withIdentifier: "PostCell", for: indexPath) as? PostCell else {
        fatalError("###\(#function): Failed to dequeue a PostCell. Check the cell reusable identifier in Main.storyboard.")
    }
    let post = dataProvider.fetchedResultsController.object(at: indexPath)
    cell.title.text = post.title
    cell.post = post
    cell.collectionView.reloadData()
    cell.collectionView.invalidateIntrinsicContentSize()
    
    if let attachments = post.attachments, attachments.allObjects.isEmpty {
        cell.hasAttachmentLabel.isHidden = true
    } else {
        cell.hasAttachmentLabel.isHidden = false
    }
    
    if sharingProvider.isShared(object: post) {
        let attachment = NSTextAttachment(image: UIImage(systemName: "person.circle")!)
        let attributedString = NSMutableAttributedString(attachment: attachment)
        attributedString.append(NSAttributedString(string: " " + (post.title ?? "")))
        cell.title.text = nil
        cell.title.attributedText = attributedString
    }
    return cell
}

18:44 - Testing the MainViewController's table view, TestMainViewController.swift

func testSharedPostsGetDisclosure() {
    var sharedObjectIDs: Set<NSManagedObjectID> = Set()
    let context = coreDataStack.persistentContainer.viewContext
    self.generatePosts(in: context, postSaveBlock: { posts in
        for (index, post) in posts.enumerated() where (index % 4) == 0 {
            sharedObjectIDs.insert(post.objectID)
        }
    })
    
    let provider = BlockBasedShareProvider(stack: coreDataStack)
    provider.isSharedBlock = sharedObjectIDs.contains
    mainViewController.sharingProvider = provider
    
    do {
        try mainViewController.dataProvider.fetchedResultsController.performFetch()
    } catch let error {
        XCTFail("Error while fetching \(error)")
    }
    
    reloadTableView()
    let rowCount = mainViewController.tableView(mainViewController.tableView,
                                                    numberOfRowsInSection: 0)
    XCTAssertEqual(100, rowCount)
    guard let expectedSharedImage = UIImage(systemName: "person.circle") else {
        XCTFail("Failed to get the person system image.")
        return
    }
    
    for index in 0..<rowCount {
        let indexPath = IndexPath(row: index, section: 0)
        let post = mainViewController.dataProvider.fetchedResultsController.object(at: indexPath)
        guard let title = post.title else {
            XCTFail("All posts should have been given a title.")
            return
        }
        
        guard let cell = mainViewController.tableView(mainViewController.tableView,
                                                           cellForRowAt: indexPath) as? PostCell else {
            XCTFail("Encountered an unexpected cell type in the main view controller's table view.")
            return
        }
        
        if sharedObjectIDs.contains(post.objectID) {
            guard let attributedText = cell.title.attributedText else {
                XCTFail("Failed to get the attributed text of \(cell). Was it not set?")
                return
            }
            
            guard let attachment = attributedText.attributes(at: 0, effectiveRange: nil)[.attachment] as? NSTextAttachment else {
                XCTFail("Expected an image attachment at the first character.")
                return
            }
            
            XCTAssertEqual(expectedSharedImage, attachment.image)
        } else {
            XCTAssertEqual(cell.title.text, title)
        }
    }
}

class BlockBasedShareProvider: SharingProvider {
    var coreDataStack: CoreDataStack
    init(stack: CoreDataStack) {
        coreDataStack = stack
    }
    
    func isShared(object: NSManagedObject) -> Bool {
        return isShared(objectID: object.objectID)
    }
    
    public var isSharedBlock: ((_ object: NSManagedObjectID) -> Bool)? = nil
    func isShared(objectID: NSManagedObjectID) -> Bool {
        guard let block = isSharedBlock else {
            return coreDataStack.isShared(objectID: objectID)
        }
        return block(objectID)
    }
    
    public var participantsBlock: ((_ object: NSManagedObject) -> [RenderableShareParticipant])? = nil
    func participants(for object: NSManagedObject) -> [RenderableShareParticipant] {
        guard let block = participantsBlock else {
            return coreDataStack.participants(for: object)
        }
        return block(object)
    }
    
    public var sharesBlock: ((_ objectIDs: [NSManagedObjectID]) -> [NSManagedObjectID: RenderableShare])? = nil
    func shares(matching objectIDs: [NSManagedObjectID]) throws -> [NSManagedObjectID: RenderableShare] {
        guard let block = sharesBlock else {
            return try coreDataStack.shares(matching: objectIDs)
        }
        return block(objectIDs)
    }
    
    public var canEditBlock: ((_ object: NSManagedObject) -> Bool)? = nil
    func canEdit(object: NSManagedObject) -> Bool {
        guard let block = canEditBlock else {
            return coreDataStack.canEdit(object: object)
        }
        return block(object)
    }
    
    public var canDeleteBlock: ((_ object: NSManagedObject) -> Bool)? = nil
    func canDelete(object: NSManagedObject) -> Bool {
        guard let block = canDeleteBlock else {
            return coreDataStack.canDelete(object: object)
        }
        return block(object)
    }
}

20:01 - CoreDataStack + Sharing, CoreDataStack.swift

extension CoreDataStack: SharingProvider {
    func isShared(object: NSManagedObject) -> Bool {
        return isShared(objectID: object.objectID)
    }

    func isShared(objectID: NSManagedObjectID) -> Bool {
        var isShared = false
        if let persistentStore = objectID.persistentStore {
            if persistentStore == sharedPersistentStore {
                isShared = true
            } else {
                let container = persistentContainer
                do {
                    let shares = try container.fetchShares(matching: [objectID])
                    if nil != shares.first {
                        isShared = true
                    }
                } catch let error {
                    print("Failed to fetch share for \(objectID): \(error)")
                }
            }
        }
        return isShared
    }
    
    func participants(for object: NSManagedObject) -> [RenderableShareParticipant] {
        var participants = [CKShare.Participant]()
        do {
            let container = persistentContainer
            let shares = try container.fetchShares(matching: [object.objectID])
            if let share = shares[object.objectID] {
                participants = share.participants
            }
        } catch let error {
            print("Failed to fetch share for \(object): \(error)")
        }
        return participants
    }
    
    func shares(matching objectIDs: [NSManagedObjectID]) throws -> [NSManagedObjectID: RenderableShare] {
        return try persistentContainer.fetchShares(matching: objectIDs)
    }
    
    func canEdit(object: NSManagedObject) -> Bool {
        return persistentContainer.canUpdateRecord(forManagedObjectWith: object.objectID)
    }
        
    func canDelete(object: NSManagedObject) -> Bool {
        return persistentContainer.canDeleteRecord(forManagedObjectWith: object.objectID)
    }
}