[英]How to invoke a class method using performSelector() on AnyClass in Swift?
在ObjC中,您可以使用NSObject
的類方法簡單地調用類方法。
[Machine performSelector:@selector(calculate:) withObject:num];
但是你如何在Swift 2.2中做到這一點?
@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)
}
使用此代碼我收到以下編譯器錯誤:
錯誤:無法使用類型為'(Selector,withObject:NSNumber)'的參數列表調用'performSelector'
我在這里錯過了什么?
AnyClass
不符合開箱即用的NSObjectProtocol
。 我必須將aClass
為NSObjectProtocol
以使用performSelector
( performSelector:withObject:
作為NSObjectProtocol
上的方法橋接到Swift):
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"
}
}
}
Swift 2.x:
(aClass as! NSObjectProtocol).performSelector(sel, withObject: num) // Unmanaged<AnyObject>(_value: 42)
更安全一點:
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
返回一個Unmanaged
對象,這就是為什么需要takeUnretainedValue()
(或者如果你想傳輸內存所有權,可選擇takeRetainedValue()
)。
如果要在機器上執行計算,只需執行以下操作:
Machine.calculate(NSNumber(integer: 1337))
如果您需要調用執行選擇器,那么執行:
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)
}
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