Question

在ObjC中，您只需使用NSObject中的类方法调用类方法。

[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：无法调用＆＃39; performSelector＆＃39;使用类型＆＃39;（Selector，withObject：NSNumber）＆＃39;
的参数列表

我在这里缺少什么？

Answer 1

userId不符合开箱即用的AnyClass。我必须将NSObjectProtocol转换为aClass才能使用NSObjectProtocol（performSelector作为performSelector:withObject:上的方法桥接到Swift：

斯威夫特3：

NSObjectProtocol

Swift 2.x：

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"
        }
    }
}

更安全一点：

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

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" } } }会返回performSelector个对象，这就是为什么Unmanaged（或者如果你想转移内存所有权，可选takeUnretainedValue()）的原因。

Answer 2

如果您想在机器上执行计算，请执行以下操作：

Machine.calculate(NSNumber(integer: 1337))

如果您需要调用执行选择器，请执行：

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)
}

如何在Swift的AnyClass上使用performSelector（）调用类方法？

2 个答案: