Swift 2.0中的关联属性

Question

I have written an extension in swift 2.0. I want to use associated property in my extension.

public typealias ShareCompletion = (result: AnyObject, error : NSError?) -> Void
private var ShareCompletionKey = "ShareCompletionKey"

extension UIViewController  {

var completionHandler : ShareCompletion? {
    get {
        return objc_getAssociatedObject(self, &ShareCompletionKey)
    }
    set {
        objc_setAssociatedObject(self, &ShareCompletionKey, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
 }
}

Unable to identify the error in the code

Following are the errors:

Cannot convert return expression of type 'AnyObject!' to return type 'ShareCompletion?'

enter code here Cannot convert value of type 'ShareCompletion?' to expected argument type 'AnyObject!'

Answer 1

there is more trouble in your code, but most important is, that AnyObject is a protocol to which all classes implicitly conform. your ShareCompletion is not a class at all

import Foundation
public typealias ShareCompletion = (result: AnyObject, error : NSError?) -> Void
private var ShareCompletionKey = "ShareCompletionKey"

let sc: ShareCompletion = { result, error in }
print(sc.dynamicType) // (AnyObject, Optional<NSError>) -> ()
sc is AnyObject // FALSE !!!!!