Swift: "This class is not key value coding-compliant..." for Double values

Question

I have a scenario in which I have a simple data object in Swift, containing multiple property variables. They are a mix of String? and Double? value types. I'm trying to retrieve the values for each property using valueForKey. My code looks something like this...

let myDataObj = ...
let stringKeyName = "myStringProperty"
let doubleKeyName = "myDoubleProperty"

guard let stringPropertyValue = myDataObj.valueForKey(stringKeyName) else {
    return
}
guard let doublePropertyValue = myDataObj.valueForKey(doubleKeyName) else {
    return
}

The first call to get stringPropertyValue works fine, and I am able to retrieve the value as expected. However, the second call to retrieve doublePropertyValue fails with an exception saying, "this class is not key value coding-compliant for the key myDoubleProperty.'"

I know that the property name is correct, and I also know that a value is set for this property. Why is it that valueForKey works on String objects, but not Double objects?

So, your data object is a subclass of NSObject? KVC is not native for swift — Anton Tyutin, Jan 14 '16 at 15:52
I've tried to do the same way. It worked for "Double", "NSNumber?", but not for "Double?". seems like native swift types can not be converted to Objective-C when they are optionals. — Anton Tyutin, Jan 14 '16 at 15:59
`Double?` type has no equevelent in Objective c. and that is the problem. — Ismail, Jan 14 '16 at 16:06

score 7 · Accepted Answer · answered Jan 14 '16 at 17:00

Correct, you can only do key value coding for types that can be represented in Objective-C. Unfortunately, those types that are represented as primitive data types in Objective-C (e.g. Swift's Int and Double are represented as NSInteger and double in Objective-C, respectively) can not be presented as such if they are optionals. In Objective-C, optionals only make sense with class types, not fundamental data types.

Swift: "This class is not key value coding-compliant..." for Double values

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