BindableObjects SwiftUI 数组答案

【问题标题】：Array of BindableObjects SwiftUIBindableObjects SwiftUI 数组
【发布时间】：2019-11-15 04:54:12
【问题描述】：

所以我正在尝试使用 SwiftUI 设置 CoreData，并且 CoreData 模型和 SwiftUI 视图都可以正常工作。我需要做的就是连接它们。我能够传递离散数量的 BindableObjects，但我需要传递一个数组。这是设置：

let peristence = PersistenceManager()
var model = [Entry]() // Entry Conforms to NSManagedObject and BindableObject
let request = Entry.createFetchRequest()
let sort = NSSortDescriptor(key: "callsign", ascending: true)
request.sortDescriptors = [sort]
do {
    model = try peristence.persistenceContainer.viewContext.fetch(request)
} catch {
    fatalError(error.localizedDescription)
}

if let windowScene = scene as? UIWindowScene {
    let window = UIWindow(windowScene: windowScene)
    window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(model))

这会产生以下错误：

实例方法'environmentObject'要求'[Entry]'符合'BindableObject'

如何使[Entry] 符合要求？

【问题讨论】：

标签： swift core-data protocols swiftui

【解决方案1】：

您可以使用实现 BindableObject 协议的 NSFetchedResultsControllerDelegate 并将更改转发到 NSFetchedResultsController

class BindableFetchedResults<ResultType>: NSObject, BindableObject, NSFetchedResultsControllerDelegate where ResultType : NSFetchRequestResult {

    let controller: NSFetchedResultsController<ResultType>
    var results: [ResultType]? {
        controller.fetchedObjects
    }
    let didChange = PassthroughSubject<Void, Never>()

    init?(fetchRequest: NSFetchRequest<ResultType>, managedObjectContext context: NSManagedObjectContext) {
        self.controller = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
        super.init()
        self.controller.delegate = self
        do {
            try controller.performFetch()
        } catch {
            return nil
        }
    }

    func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
        didChange.send()
    }
}

在代码中是这样的：


let persistence = PersistenceManager()
let request = Entry.createFetchRequest()
let sort = NSSortDescriptor(key: "callsign", ascending: true)
request.sortDescriptors = [sort]

guard let model =  BindableFetchedResults(fetchRequest: request, managedObjectContext: persistence.persistenceContainer.viewContext) else {
    fatalError()
}

if let windowScene = scene as? UIWindowScene {
    let window = UIWindow(windowScene: windowScene)
    window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(model))

然后你就可以访问model.results上的实体了

【讨论】：