Swift 4.2 responds to Selector returns false, how to check if property exists?

Question

In the following example I expect the x.responds(to: Selector(name)) to return true. However it doesn't.

x.value(forKeyPath: name) throws a signal SIGABRT error.

The same code worked in Swift 3.

My question: how do I check for properties in a class (that extends from NSObject) and retrieve them based on a string.

import UIKit

class Test: NSObject {
    var test = "test"
}

func property(_ object: Any, _ name: String) -> Bool? {
    let x = object as? NSObject

//    x?.value(forKeyPath: name)

    return x?.responds(to: Selector(name))
}

property(Test(), "test")

(code for a playground in Swift 4.2)

https://stackoverflow.com/q/30795117/1187415 – `@objc var ...` — Martin R, Jan 16 '19 at 15:50
Possibly Related (?): https://stackoverflow.com/questions/33479301/cannot-access-swift-var-from-objective-c-view-controller-ios — Ahmad F, Jan 16 '19 at 15:54
Can you just use native [`Swift 4` `KeyPath`s](https://www.klundberg.com/blog/swift-4-keypaths-and-you/)? — user28434'mstep, Jan 16 '19 at 15:55
Thanks @user28434 didn't know about KeyPaths, might use it in the future! — user3703155, Jan 17 '19 at 16:09

score 3 · Answer 1 · answered Jan 16 '19 at 15:52

Placing @objc in front of var test fixed the issues.

import UIKit

class Test: NSObject {
    @objc var test = "test"
}

func property(_ object: Any, _ name: String) -> Bool? {
    let x = object as? NSObject

    x?.value(forKeyPath: name)

    return x?.responds(to: Selector(name))
}

property(Test(), "test")

Swift 4.2 responds to Selector returns false, how to check if property exists?

1 Answers1