Error: Unrecognised Selector when using class reference

Question

我在名为 cloud 的 swift 文件中有一个 class 我在我的项目中使用对那个 class 的引用来调用它的两个方法。但是我收到以下错误并且应用程序崩溃了；

NSForwarding: warning: object 0x7fc938717160 of class 'App.Cloud' does not implement methodSignatureForSelector: -- trouble ahead

Unrecognized selector -[App.Cloud persistentStoreWillChange]

(lldb)

有谁知道我可以解决这个问题以及为什么会这样？ PS: 该错误仅在安装应用程序并首次启动时出现。如果我退出并重新启动它不会出现，但它不会执行这些方法。

这是我的 class,

class Cloud {

let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext

func persistentStoreWillChange (notification:NSNotification) {

    self.moc!.performBlock { () -> Void in
        if self.moc!.hasChanges {
            var error:NSError? = nil
            self.moc!.save(&error)
            if error != nil {
                println("Save error: \(error)")
            } else{
                // drop any manged object refrences
                self.moc!.reset()
            }

        }
    }
}

func persistentStoreDidChange () {
    println("Store Did Change")
}


//Refresh Data
func recieveChanges (notification:NSNotification){
    self.moc!.performBlock { () -> Void in
        self.moc!.mergeChangesFromContextDidSaveNotification(notification)
    }
}

//View Will Appear
func addObsevers() {

NSNotificationCenter.defaultCenter().addObserver(self, selector: "persistentStoreDidChange:", name: NSPersistentStoreCoordinatorStoresDidChangeNotification, object: nil)

 NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("persistentStoreWillChange:"), name:NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)

 NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("recieveICloudChanges:"), name:NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)

}

//View Will Dissapear
func removeObservers() {

 NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreCoordinatorStoresDidChangeNotification, object: nil)
 NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)
 NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)
}

}

Class 视图控制器中的引用：

let iCloudSync = Cloud()

override func viewWillAppear(animated: Bool) {

    iCloudSync.addObsevers()

    loadData()

}

override func viewWillDisappear(animated: Bool) {
    iCloudSync.removeObservers()
}

Answer 1

好吧，你这样做，它说当通知触发时在 self 上调用 persistentStoreDidChange：

NSNotificationCenter.defaultCenter().addObserver(self,
  selector: "persistentStoreDidChange",
  name: NSPersistentStoreCoordinatorStoresDidChangeNotification,
  object: nil)

但是你似乎没有在 class Cloud 中实现 persistentStoreDidChange。

所以要么删除那个观察者，要么实现这个方法。

Answer 2

您的方法有参数，因此您必须在名称中用“:”表示。更改后的代码应如下所示：

NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("persistentStoreWillChange:"), name: NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("recieveICloudChanges:"), name: NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)

Answer 3

声明时需要从 NSObject 派生 class Cloud，如下所示：

class Cloud : NSObject {

否则你的选择器对Objective-C是不可见的。

Answer 4

您更改了代码但忘记更改方法声明

func persistentStoreDidChange () {
    println("Store Did Change")
}

至

func persistentStoreDidChange (notification: NSNotification) {
    println("Store Did Change")
}

Error: Unrecognised Selector when using class reference

Error: Unrecognised Selector when using class reference

ios

swift

class

icloud

nsnotificationcenter