setValue:forKey 在 swift 中总是崩溃

Question

I have below use case:

class Foo: NSObject {
    var bar = ""
}

let foo = Foo()
foo.setValue("A name", forKey: "bar") //throws exception: this class is not key value coding-compliant for the key bar.
print("Foo.bar: \(foo.bar)")

Apple documentation ( here ) sais that in Swift each class subclasing NSObject becomes by default key value compliant. If so why am I getting not key value compliant exception?

Swift objects that inherit from NSObject or one of its subclasses are key-value coding compliant for their properties by default.

Am I missing something? Dose any one know which could be the problem?

Note: I tried to make the "bar" property NSString but i got the same exception.

Answer 1

To implement KVC(Key-Value Coding) support for a property. you need the @objc annotation on your property, Since the current implementation of KVC is written in Objective-C, After adding @objc , Objective-c can see it.

class Foo: NSObject {
    @objc var bar = ""
}
let foo = Foo()
foo.setValue("A name", forKey: "bar")
print("Foo.bar: \(foo.bar)")