CoreData實踐（一）

      在客戶端的開發中，我們可能要輕量級的儲存一些資料，此時最方便的想法就是使用SQLite。而在iOS平臺下，我們可以使用蘋果提供的CoreData框架。如何在專案中著手使用CoreData呢?

（1）建立一個iOS專案，同時勾選Use Core Data選項。

（2）此時可以發現在專案目錄中比之前多了一個檔案：如圖：

。

（3）來到AppDelegate.swift中，可以發現生成了大量關於CoreData的程式碼：

// MARK: - Core Data stack

  lazy var applicationDocumentsDirectory: NSURL = {
      // The directory the application uses to store the Core Data store file. This code uses a directory named "com.chenyufengweb.UsingData" in the application's documents Application Support directory.
      let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
      return urls[urls.count-1] as! NSURL
  }()

  lazy var managedObjectModel: NSManagedObjectModel = {
      // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
      let modelURL = NSBundle.mainBundle().URLForResource("UsingData", withExtension: "momd")!
      return NSManagedObjectModel(contentsOfURL: modelURL)!
  }()

  lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator? = {
      // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added 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.
      // Create the coordinator and store
      var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
      let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("UsingData.sqlite")
      var error: NSError? = nil
      var failureReason = "There was an error creating or loading the application's saved data."
      if coordinator!.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil, error: &error) == nil {
          coordinator = nil
          // Report any error we got.
          var dict = [String: AnyObject]()
          dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
          dict[NSLocalizedFailureReasonErrorKey] = failureReason
          dict[NSUnderlyingErrorKey] = error
          error = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
          // Replace this with code to handle the error appropriately.
          // abort() 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.
          NSLog("Unresolved error \(error), \(error!.userInfo)")
          abort()
      }
      
      return coordinator
  }()

  lazy var managedObjectContext: NSManagedObjectContext? = {
      // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
      let coordinator = self.persistentStoreCoordinator
      if coordinator == nil {
          return nil
      }
      var managedObjectContext = NSManagedObjectContext()
      managedObjectContext.persistentStoreCoordinator = coordinator
      return managedObjectContext
  }()

  // MARK: - Core Data Saving support

  func saveContext () {
      if let moc = self.managedObjectContext {
          var error: NSError? = nil
          if moc.hasChanges && !moc.save(&error) {
              // Replace this implementation with code to handle the error appropriately.
              // abort() 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.
              NSLog("Unresolved error \(error), \(error!.userInfo)")
              abort()
          }
      }
  }

（4）那如何在程式碼中能夠訪問到呢？在ViewController中程式碼如下：

 var context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

此時就可以使用context來訪問CoreData的方法了。

github主頁：https://github.com/chenyufeng1991  。歡迎大家訪問！