ios - 如何在 Swift 中的 AnyClass 上使用 performSelector() 调用类方法？

Question

在 ObjC 中，您可以简单地使用NSObject.

[Machine performSelector:@selector(calculate:) withObject:num];

但是你如何在 Swift 2.2 中做到这一点？

@objc(Machine) // put it here, so you can simply copy/paste into Playground
class Machine: NSObject {
    static func calculate(param: NSNumber) -> String {
        if param.integerValue > 5 {
            return "42"
        }
        return "42" // there is only 1 answer to all the questions :D
    }
}

if let aClass = NSClassFromString("Machine") {
    let sel = #selector(Machine.calculate(_:))
    let num = NSNumber(integer: 1337)
    let answer = aClass.performSelector(sel, withObject: num) // compiler error
    // let answer = aClass.calculate(num)                     // <-- this works
    print(answer)
}

使用此代码，我收到以下编译器错误：

错误：无法使用类型为“（Selector，withObject：NSNumber）”的参数列表调用“performSelector”

我在这里想念什么？

Answer 1

AnyClass不符合NSObjectProtocol开箱即用。我必须转换aClass为NSObjectProtocol使用performSelector（performSelector:withObject:作为方法桥接到 Swift NSObjectProtocol）：

斯威夫特 3：

if let aClass = NSClassFromString("Machine") {
    let sel = #selector(Machine.calculate(param:))
    let num = NSNumber(value: 1337)

    if let myClass = aClass as? NSObjectProtocol {
        if myClass.responds(to: sel) {
            let answer = myClass.perform(sel, with: num).takeRetainedValue() // this returns AnyObject, you may want to downcast to your desired type
            print(answer) // "42\n"
        }
    }
}

斯威夫特 2.x：

(aClass as! NSObjectProtocol).performSelector(sel, withObject: num) // Unmanaged<AnyObject>(_value: 42) 

更安全一点：

if let aClass = NSClassFromString("Machine") {
    let sel = #selector(Machine.calculate(_:))
    let num = NSNumber(integer: 1337)

    if let myClass = aClass as? NSObjectProtocol {
        if myClass.respondsToSelector(sel) {
            let answer = myClass.performSelector(sel, withObject: num).takeUnretainedValue()
            print(answer) // "42\n"
        }
    }
}

performSelector返回一个Unmanaged对象，这就是为什么需要（或者如果你想转移内存所有权takeUnretainedValue()可选）。takeRetainedValue()

Answer 2

如果您想在机器上执行计算，只需执行以下操作：

Machine.calculate(NSNumber(integer: 1337))

如果您需要调用执行选择器，请执行以下操作：

if let aClass = NSClassFromString("Machine") as? AnyObject
{
    let sel = #selector(Machine.calculate(_:))
    let num = NSNumber(integer: 1337)
    let answer = aClass.performSelector(sel, withObject: num)
    print(answer)
}