CoreData初次实践(一)

dowhilenet

今天我们来通过创建一个小的Demo来实践我们的CoreDate 的学习。参考书籍Core_Data_by_Tutorials

初始项目

更多关于CoreDate的基础知识

创建Core Data Stack

主要一下几个步骤:

  1. NSManagedObjectModel

  2. NSPresistentStore

  3. NSPersistentStoreCoordinator

  4. NSManagedObjectContext
    在这里就不多说每一个都是什么了,可以参考上边给出的两篇博客

Show your code

import CoreData

class CoreDadaStack {
   /// model Name
   private let modelName = "Dog Walk"
   /// Document Directory URL
   private lazy var applicationDocumentsDirectory: NSURL = {
       let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
       return urls[urls.count - 1]
   }()
   
   /// Managed Object Model
   private lazy var managedObjectModel: NSManagedObjectModel = {
       let modelURL = NSBundle.mainBundle().URLForResource(self.modelName, withExtension: "momd")
       return NSManagedObjectModel(contentsOfURL: modelURL!)!
   }()
   /// Presistent Store Coordinator
   private lazy var psc: NSPersistentStoreCoordinator = {
       let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
       let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent(self.modelName)
       do {
           let options = [NSMigratePersistentStoresAutomaticallyOption:true]
           try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: options)
       }catch {
           print("添加持久化存储区错误")
       }
       return coordinator
   }()
   /// Managed Object Context
   lazy var context: NSManagedObjectContext = {
       var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
       managedObjectContext.persistentStoreCoordinator = self.psc
       return managedObjectContext
   }()
   /**
    Save Context Data
    */
   func saveContext() {
       if context.hasChanges {
           do {
               try context.save()
           } catch let error as NSError {
               print("错误 ❌ \(error.localizedDescription)")
               abort()
           }
       }
   }
}

选择ViewController.swift添加下边代码
import CoreData

添加属性:
var managedContext: NSManagedObjectContext!

然后打开AppDelegate.swift

import CoreData
添加属性:

lazy var coreDataStack = CoreDataStack()

application(_:didFinishLaunchingWithOptions:)添加下边代码

 func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    
    let navigationController = window?.rootViewController as! UINavigationController
    let viewcontroller = navigationController.topViewController as! ViewController
    viewcontroller.managedContext = coreDataStack.context
    return true
  }

最后我们在 UIApplicationDelegate的两个方法中调用存储方法

func applicationWillTerminate(application: UIApplication) {
        coreDataStack.saveContext()
    }
    
func applicationDidEnterBackground(application: UIApplication) {
        coreDataStack.saveContext()
    }

Modeling your data

打开Dog Walk

添加 Dog Entity ,添加属性 name 类型为 String

添加 Walk Entity, 添加属性 date 类型为 Date

接下来我们完成关系。

打开 Dog Entity ,添加relationship name 为 walks Set the destination to Walk
在属性版中修改Type类型,To Many ,勾选 Ordered

打开 Walk Entity , 添加relationship name 为 dog relationship 为 Dog Set the destination as dog and the inverse as walks.

Adding managed object subclasses

command + n 选择 NSManagedObject Subclass 选择 Dog Walk model 并且选中 Dog 和 Walk entities。 语言选择 Swift

我在生成的Walk.swiftDog.swift中都重写了父类的方法,为了在生成这两个类的时候有代码提示。

override init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?) {
        super.init(entity: entity, insertIntoManagedObjectContext: context)
    }

A walk down persistence lane

如果你上边的步骤都已经完成了,那么我们就可以开始存储数据了。

首先在ViewController.swift中添加一个属性 var currentDog: Dog! 然后我们在viewDidLoad()中来添加一些数据

//创建一个 Entity
let dogEntity = NSEntityDescription.entityForName("Dog", inManagedObjectContext: managedContext)
   let dogName = "Fido"
   //首先来检查在数据库中是否存在一个名为 Fido  的狗过
       let dogFetch = NSFetchRequest(entityName: "Dog")
   dogFetch.predicate = NSPredicate(format: "name == %@", dogName)
   do{
   //执行查询
       let results = try managedContext.executeFetchRequest(dogFetch) as! [Dog]
       //如果这个狗狗存在的话直接获取赋值给 currentDog
       if results.count > 0 {
           currentDog = results.first
       }else {
       //如果不存在 则实例化一个Dog
           currentDog = Dog(entity: dogEntity!, insertIntoManagedObjectContext: managedContext)
           currentDog.name = dogName
           try managedContext.save()
       }
   }catch let error as NSError{
       print("Error:\(error)" + "description:\(error.localizedDescription)")
   }

接下来我们来实现点击添加按钮之后添加新狗狗散步时间的功能。

  @IBAction func add(sender: AnyObject) {
   //添加一个新的 Walk Entity into Core Data
    let walkEntity = NSEntityDescription.entityForName("Walk", inManagedObjectContext: managedContext)
   let walk = Walk(entity: walkEntity!, insertIntoManagedObjectContext: managedContext)
   walk.date = NSDate.timeIntervalSinceReferenceDate()
   
   //insert the new walk into the dog's walks set
   let walks = currentDog.walks!.mutableCopy() as! NSMutableOrderedSet
   walks.addObject(walk)
   currentDog.walks = walks.copy() as? NSOrderedSet
   //save the managed object context
   do {
       try managedContext.save()
   }catch let error as NSError {
       print("Could not save:\(error)")
   }
   
   tableView.reloadData()
 }

现在你运行程序,点击➕就可以看到有新的数据在列表中显示。

Deleting objects from Core Data

我们接下来就是要把我们添加的数据删除。
我们来重写下边的方法

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        if editingStyle == .Delete {
           //选择要删除的walk
           let walkToRemove = currentDog.walks![indexPath.row] as! Walk
           //删除
           managedContext.deleteObject(walkToRemove)
           do {
               //保存操作
               try managedContext.save()
           }catch let error as NSError {
               print("Could not save: \(error)")
           }
           // 删除视图中的数据
           tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
       }
 }

运行你的app 来试试吧。

完成的项目

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