Extracting NSManagedObject attribute values from NSOrderedSet

Question

I have an initializer that takes an array of Strings as a parameter. Rather than re-write the class and risk breaking things, I'd prefer to feed the initializer what it wants.

I'm trying to extract NSStrings from NSManagedObjects stored in an NSOrderedSet .

Here's what I've tried:

    let soundsToPlay = sequenceToPlay.sounds as NSOrderedSet
    for element in soundsToPlay {
        // this prints out the object in console
        print("\(element)")
        // this, doesn't give me accessors for the sound object
        // print("\(element.fileName)")
    }

I'm missing something basic, but I'm not sure what. How would I enumerate the objects in an NSOrderedSet and extract the value of the attributes for the entities contained within the set?

Answer 1

I would suggest reading the documentation on KVC (Key Value Coding) as you can write this as one line of code:

let filenameArray = soundsToPlay.valueForKey("fileName").array()

The call to valueForKey will return an NSOrderedSet of the string and then you can convert that to an array with a call to array()

Answer 2

I figured it out. I was missing a step:

let soundsToPlay = sequenceToPlay.sounds as NSOrderedSet
for element in soundsToPlay {
    // I have to tell the compiler what type of thing my thing is
    let whatIWantToAccess = element as! MyObjectINeedAccessorsFor
    print("\(whatIWantToAccess.fileName)")
}

Answer 3

那可能是因为编译器认为“元素”是NSManagedObject的实例，并且它没有fileName，请尝试显式类型转换，类似

for element: YourClass in soundsToPlay