Question

我正在使用KVO作为已在初始化期间注册的子类PFObject中的属性。

如果我使用1个物体，一切都很好。在第二个对象上我得到错误The class KVO_vs_PFObject.MyModel must be registered with registerSubclass before using Parse.我需要多个对象来观察属性。

我尝试使用属性observer(didSet)作为swift的替代方案，但编译器因为我使用托管属性而不会让我这么做。

有谁知道这段代码的用途是什么？

以下是我的代码：

import UIKit
import Parse

class MyModel : PFObject, PFSubclassing {
    static func parseClassName() -> String {
        return "MyModel"
    }
    override class func initialize() {
        var onceToken : dispatch_once_t = 0;
        dispatch_once(&onceToken) {
            self.registerSubclass()
        }
    }
    @NSManaged var property1 : String?
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        var myObject = MyModel()
        myObject.addObserver(self, forKeyPath: "property1", options: .New, context: nil)
        myObject.property1 = "Hello"
        myObject.removeObserver(self, forKeyPath: "property1")

        // If I comment these 4 lines. myObject is happy observing the property.
        var anotherObject = MyModel()
        anotherObject.addObserver(self, forKeyPath: "property1", options: .New, context: nil)
        anotherObject.property1 = "World"
        anotherObject.removeObserver(self, forKeyPath: "property1")
    }
    override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
        var n : AnyObject? = change["new"]
        switch keyPath {
        case "property1" :
            println("observed MyModel.property1 with value \(n)")
        default :
            break
        }
    }
}

Answer 1

我最终根据相关帖子使用了计算属性而不是存储属性。 Subclassing PFObject in Swift

//    @NSManaged var property1 : String?
    var property1: String? {
        get {
            return self["property1"] as? String
        }
        set {
            self["property1"] = newValue
            println("observed MyModel.property1 with value \(newValue)")
        }
    }

Answer 2

I have this in my AppDelegate in addition to the initialize(). There were some posts here that say that initialize() needs some kick-starting before getting invoked. Worth trying the following...

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


        // Override point for customization after application launc

        //-----------------Parse customizations------------------------------


        // Enable storing and querying data from Local Datastore.
        // Remove this line if you don't want to use Local Datastore features or want to use cachePolicy.
        Parse.enableLocalDatastore()

        // ****************************************************************************
        // Uncomment this line if you want to enable Crash Reporting
        // ParseCrashReporting.enable()
        //
        // Uncomment and fill in with your Parse credentials:

        //This one is for the MyAppName Parse App

        MyModel.registerSubclass()

        // Rest of the stuff...

在使用Parse之前，必须使用registerSubclass注册该类

2 个答案: