ios - MVC - 没有 UIKit 的模型文件中的 NSFetchRequest

Question

在我的 ViewController 中，我有一个函数可以获取所有“headingNumbers”(实体“Vocabulary”的一个属性)。我知道这不是好的 MVC 实践。

所以我创建了一个新的 swift 文件。我没有导入 UIKit。 Youtube Stanford - Developing iOS 9 Apps with Swift - 2, 22:53:“切勿在模型文件中导入 UI KIT，因为该模型独立于 UI”
( https://www.youtube.com/watch?v=j50mPzDMWVQ )

但是，现在我收到这些消息，例如“使用未解析的标识符‘UIApplication’”。这是有道理的，因为我没有导入 UIKit。问题是:我现在如何在我的新 swift 文件中执行提取请求。
(你现在可能是这样，我是初学者)

import Foundation
import CoreData

class QueryData {

private var selectedHeadingNumber:String = "-123456789"
private var setOfHeadingNumbers:[String] = [String]()

func getHeadingNumbers2() -> [String] {


    if let managedObjectContext = (UIApplication.sharedApplication().delegate as? AppDelegate)?.managedObjectContext {

        // Create Fetch Request
        let fetchRequest = NSFetchRequest(entityName: "Vocabulary")

        // Add Sort Descriptor
        let sortDescriptor = NSSortDescriptor(key: "headingNumber", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]

        // Execute Fetch Request
        do {
            let result = try managedObjectContext.executeFetchRequest(fetchRequest)

            for managedObject in result {
                if let foundHeadingNumber = managedObject.valueForKey("headingNumber") {

                    if let result_number = foundHeadingNumber as? NSNumber
                    {
                        let result_string = "\(result_number)"

                        if !setOfHeadingNumbers.contains(result_string) {
                            print("Headingnumber: \(foundHeadingNumber) ")
                            setOfHeadingNumbers.append(result_string)

                            print("updated selectedHeadingNumber: ", selectedHeadingNumber)
                            selectedHeadingNumber = result_string

                            // set the default lessonnumber to the first lesson
                            if selectedHeadingNumber == "-123456789" {
                                selectedHeadingNumber = result_string
                                print("updated selectedHeadingNumber: ", selectedHeadingNumber)
                            }
                        }

                    }

                    //setOfHeadingNumbers.append(first)
                }
            }

        } catch {
            let fetchError = error as NSError
            print(fetchError)
        }

    } // end of if statement

    return setOfHeadingNumbers

} // end of func

} // end of class

Answer 1

你真正需要的是NSManagedObjectContex。将其作为参数传递给方法:

func getHeadingNumbers2(inContext context: NSManagedObjectContext) -> [String]
{
    ...
}

或者将它作为依赖注入(inject)到初始化器中

class QueryData
{
    let context: NSManagedObjectContext

    init(context: NSManagedObjectContext)
    {
        self.context = context
    }

    func getHeadingNumbers2() -> [String]
    {
        let fetchRequest = NSFetchRequest(entityName: "Vocabulary")
        let result = try self.context.executeFetchRequest(fetchRequest)
        ...
    }
}