iOS 11 NSPredicate search on Swift array crashing - NSUnknownKeyException - ios

Question

I am using NSPredicate to filter an array in Swift. The problem is after updating to iOS 11 (Xcode 9 /w Swift 4), I keep getting a crash on the filter line. Here is the crash log:
Terminating app due to uncaught exception 'NSUnknownKeyException', reason: >'[ valueForUndefinedKey:]: this class is not key >value coding-compliant for the key name.'
Here is an example of the class that I have an array of:
final class Model: NSObject {
let name: String
init(name: String) {
self.name = name
}
}
Here is the code that is crashing:
let myArray = [Model(name: "Jason"), Model(name: "Brian")]
let predicate = NSPredicate(format: "name == 'Jason'")
let filteredArray = myArray.filter { predicate.evaluate(with: $0)}
Question is why is this crashing now that I updated to iOS 11?

Answer 1

After fighting with this for a while, I finally came across the answer!
A subtlety of updating to Swift 4 is that classes that are subclasses of NSObject are no longer implicitly exposed to objective-c like they were before. Because of this, you need to explicitly annotate classes/functions with #objc. The compiler will notify you of places where the annotation is needed, but not in this case.
Ultimately because of this, the key-value lookup was no longer implicitly exposed to objective-c, which is needed to filter with NSPredicate. The code below fixes the crash!
Solution 1
extension Model {
#objc override func value(forKey key: String) -> Any? {
switch key {
case "name":
return name
default:
return nil
}
}
}
Solution 2
Alternative thanks to Uros19: Instead of implementing the above function, you could annotate the property directly with #objc (e.g., #objc let name: String). You lose a little bit of clarity as to why you are annotating the property with #objc, but this is only a small consideration.
I hope this saves some people time and frustration :)