Question

我在一个名为cloud的swift文件中有一个类我在项目中使用对class的引用来调用其两个方法。但我得到以下错误，应用程序崩溃;

NSForwarding：警告：“App.Cloud”类的对象0x7fc938717160   没有实现methodSignatureForSelector： - 提前麻烦

无法识别的选择器 - [App.Cloud persistentStoreWillChange]

（LLDB）

有谁知道我能解决这个问题以及为什么会这样？ PS：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没有出现，但是它不执行这些方法。

继承我的班级，

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)
}

}

View Controller中的类引用：

let iCloudSync = Cloud()

override func viewWillAppear(animated: Bool) {

    iCloudSync.addObsevers()

    loadData()

}

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

Answer 1

当您声明它时，需要从NSObject派生dynamic_cast，如下所示：

class Cloud

否则您的选择器对于Objective-C是不可见的。

Answer 2

嗯，你执行此操作，即在通知触发时在persistentStoreDidChange上致电self：

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

但是，您似乎未在persistentStoreDidChange内实施class Cloud。

所以要么删除那个观察者，要么实现该方法。

Answer 3

您的方法有参数，因此您必须在其名称中用“：”表示。更改的代码应如下所示：

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 4

您更改了代码但忘记更改方法声明

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

到

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

错误：使用类引用时无法识别的选择器

4 个答案: