Swift closure as AnyObject

问题:

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'

回答1:

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
    )
)

回答2:

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
})

回答3:

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
}

回答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

回答5:

This has worked for me:

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

回答6:

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

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

 let block:Any? = aBlock

回答7:

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.