在聚焦中展示 app 数据

2:40 - Creating a NSCoreDataCoreSpotlightDelegate

let spotlightDelegate = NSCoreDataCoreSpotlightDelegate(forStoreWith: description,
                                                        coordinator: coordinator)
spotlightDelegate.startSpotlightIndexing()

5:24 - Adding a NSCoreDataCoreSpotlightDelegate to a CoreDataStack

import Foundation
import CoreData

class CoreDataStack {
    private (set) var spotlightIndexer: TagsSpotlightDelegate?
    
    lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "Tags")

        guard let description = container.persistentStoreDescriptions.first else {
            fatalError("###\(#function): Failed to retrieve a persistent store description.")
        }

        description.type = NSSQLiteStoreType
        description.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
        description.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
                
        container.loadPersistentStores(completionHandler: { (_, error) in
            guard let error = error as NSError? else { return }
            fatalError("###\(#function): Failed to load persistent stores:\(error)")
        })
        
        spotlightIndexer = TagsSpotlightDelegate(forStoreWith: description,
                                                 coordinator: container.persistentStoreCoordinator)

        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        
        container.viewContext.automaticallyMergesChangesFromParent = true
        do {
            try container.viewContext.setQueryGenerationFrom(.current)
        } catch {
            fatalError("###\(#function): Failed to pin viewContext to the current generation:\(error)")
        }
        
        return container
    }()
}

6:24 - Creating TagsSpotlightDelegate

class TagsSpotlightDelegate: NSCoreDataCoreSpotlightDelegate {
    override func domainIdentifier() -> String {
        return "com.example.apple-samplecode.tags"
    }

    override func indexName() -> String? {
        return "tags-index"
    }
  
    override func attributeSet(for object: NSManagedObject) -> CSSearchableItemAttributeSet? {
        if let photo = object as? Photo {
            let attributeSet = CSSearchableItemAttributeSet(contentType: .image)
            attributeSet.identifier = photo.uniqueName
            attributeSet.displayName = photo.userSpecifiedName
            attributeSet.thumbnailData = photo.thumbnail?.data
            for case let tag as Tag in photo.tags ?? [] {
                if let name = tag.name {
                    if attributeSet.keywords != nil {
                        attributeSet.keywords?.append(name)
                    } else {
                        attributeSet.keywords = [name]
                    }
                }
            }
            return attributeSet
        } else if let object as? Tag {
            let attributeSet = CSSearchableItemAttributeSet(contentType: .text)
            attributeSet.displayName = tag.name
            return attributeSet
        }
        return nil
    }
}

9:51 - Customizing PhotosViewController with Spotlight delegate functionality

class PhotosViewController: UICollectionViewController {
    @IBOutlet var generateDefaultPhotosItem: UIBarButtonItem!
    @IBOutlet var deleteSpotlightIndexItem: UIBarButtonItem!
    @IBOutlet var startStopIndexingItem: UIBarButtonItem!
    
    private var isTagging = false
    private var spotlightFoundItems = [CSSearchableItem]()
    private static let defaultSectionNumber = 0
    private var searchQuery: CSSearchQuery?
    var spotlightUpdateObserver: NSObjectProtocol?

    private lazy var spotlightIndexer: TagsSpotlightDelegate = {
        let appDelegate = UIApplication.shared.delegate as? AppDelegate
        return appDelegate!.coreDataStack.spotlightIndexer!
    }()
  
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // ...

        toggleSpotlightIndexing(enabled: true)
    }
  
    @IBAction func deleteSpotlightIndex(_ sender: Any) {
        toggleSpotlightIndexing(enabled: false)

        spotlightIndexer.deleteSpotlightIndex(completionHandler: { (error) in
            if let err = error {
                print("Encountered error while deleting Spotlight index data, \(err.localizedDescription)")
            } else {
                print("Finished deleting Spotlight index data.")
            }
        })
    }

    @IBAction func toggleSpotlightIndexingEnabled(_ sender: Any) {
        if spotlightIndexer.isIndexingEnabled == true {
            toggleSpotlightIndexing(enabled: false)
        } else {
            toggleSpotlightIndexing(enabled: true)
        }
    }

    private func toggleSpotlightIndexing(enabled: Bool) {
        if enabled {
            spotlightIndexer.startSpotlightIndexing()
            startStopIndexingItem.image = UIImage(systemName: "pause")
        } else {
            spotlightIndexer.stopSpotlightIndexing()
            startStopIndexingItem.image = UIImage(systemName: "play")
        }

        let center = NotificationCenter.default
        if spotlightIndexer.isIndexingEnabled && spotlightUpdateObserver == nil {
            let queue = OperationQueue.main
            spotlightUpdateObserver = center.addObserver(forName: NSCoreDataCoreSpotlightDelegate.indexDidUpdateNotification,
                                                         object: nil,
                                                         queue: queue) { (notification) in
                let userInfo = notification.userInfo
                let storeID = userInfo?[NSStoreUUIDKey] as? String
                let token = userInfo?[NSPersistentHistoryTokenKey] as? NSPersistentHistoryToken
                if let storeID = storeID, let token = token {
                    print("Store with identifier \(storeID) has completed ",
                          "indexing and has processed history token up through \(String(describing: token)).")
                }
            }
        } else {
            if spotlightUpdateObserver == nil {
                return
            }
            center.removeObserver(spotlightUpdateObserver as Any)
        }
    }
}

13:13 - Adding full-text search to PhotosViewController

extension PhotosViewController: UISearchResultsUpdating {
    func updateSearchResults(for searchController: UISearchController) {
        guard let userInput = searchController.searchBar.text, !userInput.isEmpty else {
            dataProvider.performFetch(predicate: nil)
            reloadCollectionView()
            return
        }
        
        let escapedString = userInput.replacingOccurrences(of: "\\", with: "\\\\").replacingOccurrences(of: "\"", with: "\\\"")
        let queryString = "(keywords == \"" + escapedString + "*\"cwdt)"
        
        searchQuery = CSSearchQuery(queryString: queryString, attributes: ["displayName", "keywords"])

        // Set a handler for results. This will be a called 0 or more times.
        searchQuery?.foundItemsHandler = { items in
            DispatchQueue.main.async {
                self.spotlightFoundItems += items
            }
        }
        
        // Set a completion handler. This will be called once.
        searchQuery?.completionHandler = { error in
            guard error == nil else {
                print("CSSearchQuery completed with error: \(error!).")
                return
            }

            DispatchQueue.main.async {
                self.dataProvider.performFetch(searchableItems: self.spotlightFoundItems)
                self.reloadCollectionView()
                self.spotlightFoundItems.removeAll()
            }
        }

        // Start the query.
        searchQuery?.start()
    }
}