SwiftUI 和函数 - 在范围内找不到“viewContext”

Question

我想将我的函数与 SwiftUI 视图分开。我有这个功能：

import Foundation
import CoreData

func deleteAll() {
    let fetchRequestItems: NSFetchRequest<NSFetchRequestResult> = Item.fetchRequest()
    let deleteRequestItems = NSBatchDeleteRequest(fetchRequest: fetchRequestItems)
    
    do {
        try viewContext.save()
        try viewContext.execute(deleteRequestItems)
        viewContext.reset()
    } catch let error as NSError {
        print(error)
    }
}

我在 viewContext 的 3 行上遇到错误：

在范围内找不到“viewContext”

当它在 SwiftUI 视图中时，同样的功能也可以工作。但是视图的 viewContext 是这样注入的：

ContentView()
.environment(\.managedObjectContext, persistenceController.container.viewContext)

所以问题是： 如何在单独的 Swift 文件中的函数内部注入/使用 Core Data Context (viewContext)？

编辑： Persistence.swift 来自 SwiftUI 2.0 模板，如下所示：

import CoreData

struct PersistenceController {
    static let shared = PersistenceController()

    static var preview: PersistenceController = {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        for _ in 0..<10 {
            let newItem = Item(context: viewContext)
            newItem.timestamp = Date()
        }
        
        do {
            try viewContext.save()
        } catch {
            // Replace this implementation with code to handle the error appropriately.
            // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return result
    }()

    let container: NSPersistentCloudKitContainer

    init(inMemory: Bool = false) {
        container = NSPersistentCloudKitContainer(name: "Moneto")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

                /*
                Typical reasons for an error here include:
                * The parent directory does not exist, cannot be created, or disallows writing.
                * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                * The device is out of space.
                * The store could not be migrated to the current model version.
                Check the error message to determine what the actual problem was.
                */
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
    }
}

Answer 1

您应该将托管上下文注入到您的函数中

func deleteAll(viewContext: NSManagedObjectContext) {
    //…
}

这还为您提供了一个优势，即如果您正在使用背景或子上下文，您可以选择从哪个上下文中删除

Answer 2

在你的视图中添加这个变量

@Environment(\.managedObjectContext) var viewContext