Swift closure as AnyObject

Question

Im trying to use this method: class_addMethod() which in Obj-c is used like this:

class_addMethod([self class], @selector(eventHandler), imp_implementationWithBlock(handler), "v@:");

And Im using it like this in Swift:

class_addMethod(NSClassFromString("UIBarButtonItem"), "handler", imp_implementationWithBlock(handler), "v@:")

It is an extension for UIBarButtonItem as you might have figured out.

imp_implementationWithBlock takes a parameter of type AnyObject!

How can I cast ()->() into AnyObject ?

I've tried to cast it like this: handler as AnyObject but it gives me an error saying: ()->() does not conform to protocol 'AnyObject'

Did you try using `reinterpretCast()`? – Romain Jan 29 '15 at 10:38 — Romain, Jan 29 '15 at 10:38

score 11 · Accepted Answer · answered Jan 29 '15 at 10:49

11

How can I cast ()->() into AnyObject ?

Warning: This answer includes undocumented and unsafe feature in Swift. I doubt this passes AppStore review.

let f: ()->() = {
    println("test")
}

let imp = imp_implementationWithBlock(
    unsafeBitCast(
        f as @objc_block ()->(),
        AnyObject.self
    )
)

answered Jan 29 '15 at 10:49

rintaro

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What is 'f' ? Is it the closure? – Arbitur Jan 29 '15 at 10:51
So why has Apple a `func imp_implementationWithBlock(_ block: AnyObject!) -> IMP` in the lib reference if you need that code you posted? Bug? – qwerty_so Jan 29 '15 at 10:57
Obj-C code can passes Blocks to Swift `AnyObject` type parameter. – rintaro Jan 29 '15 at 11:06
If you want to add this as an extension you are free to use it: `extension UIBarButtonItem { convenience init(title: String?, style: UIBarButtonItemStyle, handler: ()->()) { let imp = imp_implementationWithBlock(unsafeBitCast(handler as @objc_block ()->(), AnyObject.self)) class_addMethod(UIBarButtonItem.self, "handler", imp, "v@:") self.init(title: title, style: style, target: nil, action: "handler") self.target = self } }` – Arbitur Jan 29 '15 at 11:12
I'm not sure this extension does work as you expected. As far as I know, Method is class wide property, not instance local. So I think this results every instance shares same handler, no? – rintaro Jan 29 '15 at 11:17
Hmm maybe the method will be created for every but only the ones I add the handler to will try to call it. But I will test it further. – Arbitur Jan 29 '15 at 11:20
1

Should use `@convention` instead of `@objc_block` – onmyway133 Jan 16 '16 at 09:46

score 8 · Answer 2 · edited Feb 18 '16 at 09:50

8

You could write a wrapper, then pass it to the function

class ObjectWrapper<T> {
    let value :T
    init(value:T) {
       self.value = value
    }
}

let action = ObjectWarpper(value: {()->() in    
    // something
})

edited Feb 18 '16 at 09:50

Rudolf Adamkovič

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answered Sep 08 '15 at 09:55

leavez

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score 6 · Answer 3 · answered Jan 16 '16 at 09:54

In Swift 2, you should use @convention instead of @objc_block. See Type Attribute

func swizzle(type: AnyClass, original: Selector, methodType: MethodType, block: () -> Void) {
    let originalMethod = method(type, original: original, methodType: methodType)

    let castedBlock: AnyObject = unsafeBitCast(block as @convention(block) () -> Void, AnyObject.self)

    let swizzledImplementation = imp_implementationWithBlock(castedBlock)
    // More code goes here
}

score 4 · Answer 4 · answered Jan 29 '15 at 10:34

4

You can't. You can only cast it to Any.

AnyObject can represent an instance of any class type.
Any can represent an instance of any type at all, including function types.

Apple Inc. „The Swift Programming Language.“ iBooks. https://itun.es/de/jEUH0.l

answered Jan 29 '15 at 10:34

qwerty_so

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But is there another way of doing this in any way? – Arbitur Jan 29 '15 at 10:41
Have you tried to pass `Selector("handler")`? Can you show the signature of `imp_implementationWithBlock `? – qwerty_so Jan 29 '15 at 10:42
The error isnt the selector part, its the imp_implementationWithBlock() that is causing confuson – Arbitur Jan 29 '15 at 10:45
imp_implementationWithBlock(block: AnyObject!) takes only an AnyObject as parameter and returns an IMP – Arbitur Jan 29 '15 at 10:47
Its found in Objective-C Runtime references – Arbitur Jan 29 '15 at 10:47

score 2 · Answer 5 · answered Aug 15 '15 at 00:31

2

This has worked for me:

let myBlock: @objc_block () -> Void = { 
}
var mf : AnyObject = unsafeBitCast(myBlock, AnyObject.self)

answered Aug 15 '15 at 00:31

EPage_Ed

1,173
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score 1 · Answer 6 · answered Sep 28 '18 at 06:36

In Swift 4.x (I think works in 3.x too), simply declaring the closure as @convention(block) should be enough to address compatibility thing:

// define the new implementation
let handler: @convention(block) (UIBarButtonItem) -> Void = { _ in }

// inject it into the class
class_addMethod(NSClassFromString("UIBarButtonItem"), sel_registerName("handler"), imp_implementationWithBlock(handler), "v@:")

Though, starting with Swift 3, AnyObject was converted to Any if the reference comes from Objective-C, so the code will compile even without the @convention(block) part, however it will crash at runtime as the compiler will not convert the Swift closure to an Objective-C block.

score 0 · Answer 7 · answered Apr 27 '16 at 11:57

0

Use Any object (The protocol to which all types implicitly conform)

 let aBlock: (view: View) -> Void = { view in /**/ }

 let block:Any? = aBlock

answered Apr 27 '16 at 11:57

odemolliens

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Swift closure as AnyObject

7 Answers7

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