Swift 中的 parse.com - 是否可以将检索到的 PFObject 转换为子类？

Question

我创建了 PFObject 的子类，基本上遵循parse.com docs 上的说明，并将对象固定在本地。解析文档似乎没有涉及检索 PFObject 子类，我想知道 - 是否可以将检索到的对象转换为 PFObject 子类。如果有，怎么做？

（我知道如果不可能，可能需要根据检索到的 PFObject 属性重新实例化子类。）

   let query = PFQuery(className:Armor.parseClassName())
    query.fromLocalDatastore()
    query.findObjectsInBackgroundWithBlock({
        (objects:[AnyObject]?, error: NSError?) in
        if let error = error {
            // There was an error
        } else {
            if let objects = objects as? [PFObject] {
                for object in objects {
                    //This println is outputting to the console:
                    println("PFObject object retrieved")
                    if let object = object as? Armor {
                          //This println is NOT outputting to the console:
                          println("PFObject object cast as Armor")
                    }
                }
            }
        }
    })

Answer 1

确保您已在 application:didFinishLaunchingWithOptions: 中注册了子类。就我而言，它不会将检索到的对象转换为 PFObject 子类。

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    Armor.registerSubclass()

    Parse.enableLocalDatastore()
    Parse.setApplicationId(..., clientKey: ...)

    return true
}

AppDelegate.swift

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    CatsObject.registerSubclass()

    Parse.enableLocalDatastore()
    Parse.setApplicationId("...", clientKey: "...")

    return true
}

CatsObject.swift

import Foundation

class CatsObject: PFObject, PFSubclassing {
    static func parseClassName() -> String {
        return "Cat"
    }
}

CatViewController.swift

override func viewDidLoad() {
    queryData()
}

func queryData() {
    let query = PFQuery(className: CatsObject.parseClassName())
    query.fromLocalDatastore()
    query.findObjectsInBackgroundWithBlock({
        (objects:[AnyObject]?, error: NSError?) in
        if let error = error {
            // There was an error
        } else {
            println("count local objects = \(objects?.count)")
            if let objects = objects as? [PFObject] {
                for object in objects {
                    println("PFObject object retrieved")
                    if object is CatsObject {
                        println("object is CatsObject subclass")
                    }

                    if let object = object as? CatsObject {
                        println("PFObject object cast as CatsObject")
                    }
                }
            }
        }
    })
}

控制台输出

count local objects = Optional(10)
PFObject object retrieved
object is CatsObject subclass
PFObject object cast as CatsObject