swift - Swift 中获取数组的 Element 类型(通过反射)

Question

假设我有以下代码

class Foo {
}

var fooArray : Array<Foo> = Array<Foo>()
// This is important because in my code I will get Any (vs Array<Foo)
var fooArrayAny : Any = foo

我希望能够从变量 fooArrayAny 中获取 Foo 类型。

如果我有 fooArray，我会做类似的事情:

let type = fooArray.dynamicType.Element().dynamicType

但是，这不适用于 fooArrayAny。它说它没有成员 Element()

Answer 1

如果将 NSObject 设置为 Foo 的基类，则可以使用以下代码:

class EVReflectionTests: XCTestCase {    
    func testArrayInstance() {
        let fooArray : Array<Foo> = Array<Foo>()
        let fooArrayAny : Any = fooArray
        if let arr = fooArray as? Array {
            let i = arr.getArrayTypeInstance(arr)
            print("i = \(i)")
        }
    }
}

class Foo: NSObject {
}



extension Array {
    public func getArrayTypeInstance<T>(arr:Array<T>) -> T {
        return arr.getTypeInstance()
    }

    public func getTypeInstance<T>() -> T {
        let nsobjectype : NSObject.Type = T.self as! NSObject.Type
        let nsobject: NSObject = nsobjectype.init()
        return nsobject as! T
    }
}

此代码是我的库 EVReflection 的片段

更新:

我注意到上面的代码中有一个错误。我使用 fooArray 而不是 fooArrayAny。当将其更改为 fooArrayAny 时，我得到与您相同的错误，编译器没有该元素。经过一番尝试后，我找到了一个可行的解决方案。它再次包含我的 EVReflection 的部分代码图书馆。

class EVReflectionTests: XCTestCase {    
    func testArrayInstance() {
        let fooArray : Array<Foo> = Array<Foo>()
        let fooArrayAny : Any = fooArray

        if let _ = fooArrayAny as? NSArray {
            var subtype: String = "\(Mirror(reflecting: fooArrayAny))"
            subtype = subtype.substringFromIndex((subtype.componentsSeparatedByString("<") [0] + "<").endIndex)
            subtype = subtype.substringToIndex(subtype.endIndex.predecessor())
            print("The type of the array elements = \(subtype)")
            if let instance = swiftClassFromString(subtype) {
                print("An instance of the array element = \(instance)")
                let type = instance.dynamicType
                print("An instance of the array element = \(type)")
            }
        }
    }

    // All code below is a copy from the EVReflection library.

    func swiftClassFromString(className: String) -> NSObject? {
        var result: NSObject? = nil
        if className == "NSObject" {
            return NSObject()
        }
        if let anyobjectype : AnyObject.Type = swiftClassTypeFromString(className) {
            if let nsobjectype : NSObject.Type = anyobjectype as? NSObject.Type {
                let nsobject: NSObject = nsobjectype.init()
                result = nsobject
            }
        }
        return result
    }

    func swiftClassTypeFromString(className: String) -> AnyClass! {
        if className.hasPrefix("_Tt") {
            return NSClassFromString(className)
        }
        var classStringName = className
        if className.rangeOfString(".", options: NSStringCompareOptions.CaseInsensitiveSearch) == nil {
            let appName = getCleanAppName()
            classStringName = "\(appName).\(className)"
        }
        return NSClassFromString(classStringName)
    }

    func getCleanAppName(forObject: NSObject? = nil)-> String {
        var bundle = NSBundle.mainBundle()
        if forObject != nil {
            bundle = NSBundle(forClass: forObject!.dynamicType)
        }

        var appName = bundle.infoDictionary?["CFBundleName"] as? String ?? ""
        if appName == "" {
            if bundle.bundleIdentifier == nil {
                bundle = NSBundle(forClass: EVReflection().dynamicType)
            }
        appName = (bundle.bundleIdentifier!).characters.split(isSeparator: {$0 == "."}).map({ String($0) }).last ?? ""
        }
        let cleanAppName = appName
            .stringByReplacingOccurrencesOfString(" ", withString: "_", options: NSStringCompareOptions.CaseInsensitiveSearch, range: nil)
            .stringByReplacingOccurrencesOfString("-", withString: "_", options: NSStringCompareOptions.CaseInsensitiveSearch, range: nil)
        return cleanAppName
    }
}

class Foo: NSObject {
}

此代码的输出将是:

The type of the array elements = Foo
An instance of the array element = <EVReflection_iOS_Tests.Foo: 0x7fd6c20173d0>
An instance of the array element = Foo