@convention 使用-在 Swift 中通過 perform(selector, withObject)傳遞閉包參數(shù)

最近在使用開發(fā)過程中碰到這樣一個問題：向一個修飾為 @objc 的方法中傳入一個閉包參數(shù),示例代碼如下：

class SomeClass: NSObject {
    @objc func foo() {
        print("foo...")
        let selectorName = "bar:"
        let selector = Selector(selectorName)
        if self.responds(to: selector) {
            let closure = { () in
                print("block")
            }
            self.perform(selector, with: closure) //this will take error
            //self.bar(block)
        }
    }

    @objc func bar(_ arg1:@escaping ()->()) {
        print("bar...")
        arg1()
    }
}

let someClass = SomeClass()
someClass.foo()

如果通過 self.perform(selector, with:block) 方法動態(tài)調(diào)用 bar 方法并傳遞closure 的話盛龄，會報錯饰迹。

error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=1, address=0x8).

但是如果直接通過 self.bar(block) 進行調(diào)用則不會有問題。

最終在
# How to pass closure as a parameter in perform(selector, withObject)
# How to pass block arguments through performSelector?

找到了原因：
Swift 中的 closure 閉包與 Objective-C 中的 block 并不相同余舶，因此不能在運行時階段作為id類型的參數(shù)傳遞給一個接收id類型參數(shù)的方法啊鸭。

This method is the same as perform(_:) except that you can supply an argument for aSelector. aSelector should identify a method that takes a single argument of type id.id is a pointer to an objective-c object. From Swift, you are going to be limited to passing objects that inherit from NSObject. A closure does not meet those requirements.

解決辦法兩種：

使用 @convention 對 Swift 中的閉包進行修飾

let closure = {
    print("block")
}
let block: @convention(block) () -> () = closure
self.perform(selector, with: block)

關(guān)于 @convention 說明可以參考 # 每周 Swift 社區(qū)問答：@convention

@convention特性是在 Swift 2.0 中引入的，用于修飾函數(shù)類型匿值，它指出了函數(shù)調(diào)用的約定莉掂。用在以下幾個地方：
修飾 Swift 中的函數(shù)類型，調(diào)用 C 的函數(shù)時候千扔，可以傳入修飾過@convention(c)的函數(shù)類型，匹配 C 函數(shù)參數(shù)中的函數(shù)指針库正。
修飾 Swift 中的函數(shù)類型曲楚，調(diào)用 Objective-C 的方法時候，可以傳入修飾過@convention(block)的函數(shù)類型褥符，匹配 Objective-C 方法參數(shù)中的 block 參數(shù)

2.自定義一個Block類對 Swift 中的閉包進行包裝

class Block: NSObject {
    let block: () -> ()
    init(block: @escaping () -> ()) {
        self.block = block
        super.init()
    }
}

class SomeClass: NSObject {
    @objc func foo() {
        print("foo...")
        let selectorName = "bar:"
        let selector = Selector(selectorName)
        if self.responds(to: selector) {
            let block = Block {
                print("block")
            }
            self.perform(selector, with: block)
        }
    }

    @objc func bar(_ arg1: Block) {
        print("bar...")
        arg1.block()
    }
}

let someClass = SomeClass()
someClass.foo()

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