ios – 使用Swift 3在Xcode 8中寻找关于修订的NSPersistentContainer的清晰教程

我查看了Apple的：

Xcode 8发行说明：
https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Introduction.html

从Swift 2.2迁移到Swift 2.3或Swift 3
https://swift.org/migration-guide/

在macOS 10.12,iOS 10.0,tvOS 10.0和watchOS 3.0https://developer.apple.com/library/content/releasenotes/General/WhatNewCoreData2016/ReleaseNotes.html#//apple_ref/doc/uid/TP40017342-CH1-DontLinkElementID_1中的核心数据有什么新功能

还有很多其他……但是,核心数据编程指南Apple应该提供的一个文档尚未从Swift 2.https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/CoreData/FetchingObjects.html#//apple_ref/doc/uid/TP40001075-CH6-SW1更新

理想情况下,我正在寻找类似的东西,但对于Swift 3.
https://www.raywenderlich.com/115695/getting-started-with-core-data-tutorial

任何线索都会非常感激.

每个汤姆的评论(下面)我错过了什么步骤？

1)创建一个新项目“测试”

2)选择使用CoreDate(这会创建Test.xcdatamodeld)

这将使用以下内容自动填充AppDelegate(删除默认注释)：

func applicationWillTerminate(_ application: UIApplication) {
self.saveContext()
}
lazy var persistentContainer: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "Test")
    container.loadPersistentStores(completionHandler: { (storeDescription,error) in
        if let error = error as NSError? {
            fatalError("Unresolved error \(error),\(error.userInfo)")
        }
    })
    return container
}()
func saveContext () {
    let context = persistentContainer.viewContext
    if context.hasChanges {
        do {
            try context.save()
        } catch {
            let nserror = error as NSError
            fatalError("Unresolved error \(nserror),\(nserror.userInfo)")
        }
    }
}

3)创建实体“Foo”

4)添加属性“bar”类型String

5)在ViewController.swift下添加以下内容(这是从Apple复制的,我只是将“… use”替换为“print”)

func findAnimals() {
    let request: NSFetchRequest<Foo> = Foo.fetchRequest
    do {
        let searchResults = try context.fetch(request)
        print(searchResults)
    } catch {
        print("Error with request: \(error)")
    }
}

6)在override func viewDidLoad()下添加findAnimals().

但是这有错误：

> NSFetchRequest<使用未声明类型'NSFetchRequest'
> context<使用未解析的标识符“上下文”
7)所以你回过头来向viewController下的函数添加一些东西以使容器可访问(这不是示例形式的Apple).

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

很好,我们清除了2错误中的1,但错误“使用未声明的类型’NSFetchRequest’”仍然存在.

这就是我被困住的地方.即使在审查了所有Apple发布的材料后,我也找不到完整的例子.

解决方法

@Aaron再次感谢视频链接,让我走上正轨.下面是使用Xcode 8中的Swift 3从核心数据中获取,添加和清除所需的最低限度的快速浏览.

>新项目> iOS单一视图应用程序
>产品名称：“样品”
>使用核心数据(已选中)
>保存
>打开Sample.xcdatamodeld
>添加和实体：“SampleEntity”
>使用数据模型检查器将Codegen(在Class下)设置为“Class DeFinition”
>在新实体下创建一个属性：“sampleAttribute”
>打开ViewController.swift
>在“import UIKit”下添加“import CoreData”
>在Class ViewController下添加以下内容：

let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

// Get data from he attribute
func getSample() {
    let request: NSFetchRequest = SampleEntity.fetchRequest()
    request.resultType = NSFetchRequestResultType.dictionaryResultType
    do {
        let searchResults = try context.fetch(request as! NSFetchRequest<NSFetchRequestResult>) as! [NSDictionary]
        let searchResultsArray = searchResults.map { $0["sampleAttribute"] as! String}
        print("searchResultsArray",searchResultsArray)
    } catch {
        print("Error with request: \(error)")
    }
}

// Save to the attribute
func setSample() {
    let saveSample = SampleEntity(context: context)
    saveSample.sampleAttribute = "Save a new string."
    do {
        try context.save()
    } catch {
         print("Error with save: \(error)")
    }
}

// clear the attribute
func resetSample() {
    let clearSample: NSFetchRequest = SampleEntity.fetchRequest()
    let deleteResults = NSBatchDeleteRequest(fetchRequest: clearSample as! NSFetchRequest<NSFetchRequestResult>)
    do {
        try context.execute(deleteResults)
        try context.save()
    } catch {
        print("Error with save: \(error)")
    }
}

>在override func viewDidLoad()下添加以下内容：

getSample()
setSample()
getSample()
resetSample()
getSample()

>运行,您将在调试区域中看到以下内容：

searchResultsArray []                       // Initially the attribute is empty
searchResultsArray ["Save new string."]     // The attribute Now contains the string 
searchResultsArray []                       // This attribute has been cleared