列出一个类的所有子类

Question

我可以返回一个类的所有子类的列表吗？例如:

class Mother {

}

class ChildFoo: Mother {

}

class ChildBar: Mother {

}

let motherSubclasses = ... // TODO
print(motherSubclasses) // should to return [ChildFoo.self, ChildBar.self]

Answer 1

令人惊讶的是,Objective-C运行时函数与Swift类一样工作,即使它们不是子类NSObject.此外,Swift中的所有类似乎都源自SwiftObject.SwiftObject本身没有超类.

首先,一个处理ObjC运行时函数的包装器结构:

import Foundation

struct ClassInfo : CustomStringConvertible, Equatable {
    let classObject: AnyClass
    let className: String

    init?(_ classObject: AnyClass?) {
        guard classObject != nil else { return nil }

        self.classObject = classObject!

        let cName = class_getName(classObject)!
        self.className = String(cString: cName)
    }

    var superclassInfo: ClassInfo? {
        let superclassObject: AnyClass? = class_getSuperclass(self.classObject)
        return ClassInfo(superclassObject)
    }

    var description: String {
        return self.className
    }

    static func ==(lhs: ClassInfo, rhs: ClassInfo) -> Bool {
        return lhs.className == rhs.className
    }
}

以下是如何使用它:

class Mother { }
class ChildFoo: Mother { }
class ChildBar: Mother { }

class AnIrrelevantClass { }

let motherClassInfo = ClassInfo(Mother.self)!
var subclassList = [ClassInfo]()

var count = UInt32(0)
let classList = objc_copyClassList(&count)!

for i in 0..<Int(count) {
    if let classInfo = ClassInfo(classList[i]),
        let superclassInfo = classInfo.superclassInfo,
        superclassInfo == motherClassInfo
    {
        subclassList.append(classInfo)
    }
}

print(subclassList)

这只是执行浅层搜索,所以它不会扫除孙子类,但你明白了.

Answer 2

Jean Le Moignan 代码的优化版本

    static func subclasses<T>(of theClass: T) -> [T] {
        var count: UInt32 = 0, result: [T] = []
        let allClasses = objc_copyClassList(&count)!
        let classPtr = address(of: theClass)

        for n in 0 ..< count {
            let someClass: AnyClass = allClasses[Int(n)]
            guard let someSuperClass = class_getSuperclass(someClass), address(of: someSuperClass) == classPtr else { continue }
            result.append(someClass as! T)
        }

        return result
    }

public func address(of object: Any?) -> UnsafeMutableRawPointer{
    return Unmanaged.passUnretained(object as AnyObject).toOpaque()
}

对于每种类型，运行时只有一个元类实例，因此，它们上的指针是唯一的。由于某种原因===，AnyClass 不允许使用运算符，但我们可以直接比较指针

性能测试：

        let start = CFAbsoluteTimeGetCurrent()
        let found = RuntimeUtils.subclasses(of:UIViewController.self)
        let diff = CFAbsoluteTimeGetCurrent() - start
        print("Took \(diff) seconds, \(found.count) found")

输出：

字符串（描述：theClass）： Took 1.0465459823608398 seconds, 174 found

地址(of: theClass): Took 0.2642860412597656 seconds, 174 found