About performSelector return value

Question

Everyone knows that ios making support for "performSelector" in swift2.0 I want to know how can get the performSelector return value?

let returnValue:Unmanaged<AnyObject> = (self.dataSource?.performSelector("myselector:", withObject: self))!
let value : Int? = returnValue.takeRetainedValue() as? Int

There is a crash at the last line, How can I get the value from "performSelector" in swift2.0?

Answer 1

I think currently the performSelector in Swift only supports return value conforming to AnyObject, in your case you have Int which does not. In this case, performSelector will return nil, and your code is explicitly unwrapping the Optional making the program crash.

So one way to work around this is to make a method that returns NSNumber.

You can try this code in playground:

@objc class B: NSObject {
  func myselector(arg: A) -> NSNumber {
    return 0
  }
}

@objc class A: NSObject {
  var dataSource: B? = B()
  func a() -> Int {
    let returnValue = self.dataSource?.performSelector("myselector:", withObject: self)
    let value = returnValue?.takeRetainedValue() as! NSNumber
    return value.integerValue
  }
}

A().a()

Answer 2

Use takeUnretainedValue:

let foo = Foo()
let value = foo.performSelector(Selector("bar")) //type of value is Unmanaged<AnyObject?>
let uvalue = value.takeUnretainedValue() //type of uvalue is now AnyObject?
let result = value as? String //type of result is now String

Updated for Swift 5:

also works with NSSelectorFromString: say you have a UIViewController called aViewController.

let value = aViewController.perform(NSSelectorFromString("view")) //type of value is Unmanaged<AnyObject?>
let uvalue = value.takeUnretainedValue() //type of uvalue is now AnyObject?
let myView = value as? UIView //type of result is now UIView