Storage Data

iOS有四種儲存的方式：NSUserDefaults、Sqlite、CoreData、讀寫File

NSUerDefaults：適合儲存單一使用者的基本設定，但是不適合儲存多個使用者的資訊。簡單使用。

• 儲存值
  • UserDefaults.standard.set(Any?, forKey: String)

• 讀取值

  • UserDefaults.standard.string(forKey: String)

    使用set不會馬上儲存，需要調用

CoreData：

• 出現filenames are used to distinguish private declarations with the same name的錯誤解法

  • Delete your CoreData subclasses
  • Delete your derived data folder
  • Clean your project (CMD+K)

  • Generate new CoreData subclasses, this time select

    Codegen: Manual/Noneand Module: Current Product Module

• 在未使用CoreData的現有專案內新增Core Data：
  • 先在 AppDelegate.swift 內新增 import CoreData
  • 再將下面程式碼取代 AppDelegate.swift 的原有內容

//  AppDelegate.swift
//  CoreDataDemo

import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
        // Saves changes in the application's managed object context before the application terminates.
        self.saveContext()
    }

    // MARK: - Core Data stack

    lazy var persistentContainer: NSPersistentContainer = {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
        */
        let container = NSPersistentContainer(name: "CoreDataDemo")
        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)")
            }
        })
        return container
    }()

    // MARK: - Core Data Saving support

    func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.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)")
            }
        }
    }
}

然後記得更改let container = NSPersistentContainer(name: "CoreDataDemo") 中的 name 參數成你的 Porject Name。

最後在 applicationWillTerminate 函式
內，新增 self.saveContext()。

• CoreData Autogen 檔案
  • 在CoreDataDemo.xcdatamodeld替Entity用Editor-> Create NSManagedObject Subclass時，自動產生的檔案EntityProperties.swift在build會錯誤時，需要更改Data Model Inspector的Module欄位為空白，Codegen為Manual/None
• Relationship delete rules
  • Deny: Destination至少有一筆資料的情況下，就不刪除Source
  • Nullify: 刪除Relationship但是不刪除objects (Destination or Source)
  • Cascade: 刪除Source的時候一併刪除Detination
  • No Action: 刪除Source的時候，什麼都不對Destinationy做