有没有办法在Swift中设置关联的对象？
从目标C开始，你可以在两个对象之间调用函数objc_setAssociatedObject来让它们维护一个引用，如果在运行时你不希望一个对象被销毁直到它的引用被删除，那么这个引用可以很方便。 swift有没有类似的东西？
这是一个简单但完整的例子，来自jckarter的答案 。
它显示了如何添加一个新的属性到现有的类。 它通过在扩展块中定义一个计算属性来实现。 计算出的属性存储为关联的对象：
import ObjectiveC // Declare a global var to produce a unique address as the assoc object handle private var AssociatedObjectHandle: UInt8 = 0 extension MyClass { var stringProperty:String { get { return objc_getAssociatedObject(self, &AssociatedObjectHandle) as! String } set { objc_setAssociatedObject(self, &AssociatedObjectHandle, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC) } } }
编辑：
如果您需要支持获取未初始化属性的值，并避免unexpectedly found nil while unwrapping an Optional value错误，则可以像下面这样修改getter：
get { return objc_getAssociatedObject(self, &AssociatedObjectHandle) as? String ?? "" }
该解决scheme也支持所有的值types ，而不仅仅是那些自动桥接的值，比如String，Int，Double等。
包装
import ObjectiveC final class Lifted<T> { let value: T init(_ x: T) { value = x } } private func lift<T>(x: T) -> Lifted<T> { return Lifted(x) } func setAssociatedObject<T>(object: AnyObject, value: T, associativeKey: UnsafePointer<Void>, policy: objc_AssociationPolicy) { if let v: AnyObject = value as? AnyObject { objc_setAssociatedObject(object, associativeKey, v, policy) } else { objc_setAssociatedObject(object, associativeKey, lift(value), policy) } } func getAssociatedObject<T>(object: AnyObject, associativeKey: UnsafePointer<Void>) -> T? { if let v = objc_getAssociatedObject(object, associativeKey) as? T { return v } else if let v = objc_getAssociatedObject(object, associativeKey) as? Lifted<T> { return v.value } else { return nil } }
可能的类扩展 （使用示例）
extension UIView { private struct AssociatedKey { static var viewExtension = "viewExtension" } var referenceTransform: CGAffineTransform? { get { return getAssociatedObject(self, associativeKey: &AssociatedKey.viewExtension) } set { if let value = newValue { setAssociatedObject(self, value: value, associativeKey: &AssociatedKey.viewExtension, policy: objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC) } } } }
显然，这只适用于Objective-C对象。 在摆弄这一点之后，下面是如何在Swift中进行调用：
import ObjectiveC // Define a variable whose address we'll use as key. // "let" doesn't work here. var kSomeKey = "s" … func someFunc() { objc_setAssociatedObject(target, &kSomeKey, value, UInt(OBJC_ASSOCIATION_RETAIN)) let value : AnyObject! = objc_getAssociatedObject(target, &kSomeKey) }
在Swift 3.0中更新例如这是一个UITextField
import Foundation import UIKit import ObjectiveC // Declare a global var to produce a unique address as the assoc object handle var AssociatedObjectHandle: UInt8 = 0 extension UITextField { var nextTextField:UITextField { get { return objc_getAssociatedObject(self, &AssociatedObjectHandle) as! UITextField } set { objc_setAssociatedObject(self, &AssociatedObjectHandle, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC) } } }
Klaas的答案只是Swift 2.1：
import ObjectiveC let value = NSUUID().UUIDString var associationKey: UInt8 = 0 objc_setAssociatedObject(parentObject, &associationKey, value, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC) let fetchedValue = objc_getAssociatedObject(parentObject, &associationKey) as! String
只需在brindging头文件中添加#import <objc/runtime.h>即可访问swift代码下的objc_setAssociatedObject
上面的朋友已经回答了您的问题，但是如果与封闭属性有关，请注意：
“`
import UIKit public extension UICollectionView { typealias XYRearrangeNewDataBlock = (_ newData: [Any]) -> Void typealias XYRearrangeOriginaDataBlock = () -> [Any] // MARK:- associat key private struct xy_associatedKeys { static var originalDataBlockKey = "xy_originalDataBlockKey" static var newDataBlockKey = "xy_newDataBlockKey" } private class BlockContainer { var rearrangeNewDataBlock: XYRearrangeNewDataBlock? var rearrangeOriginaDataBlock: XYRearrangeOriginaDataBlock? } private var newDataBlock: BlockContainer? { get { if let newDataBlock = objc_getAssociatedObject(self, &xy_associatedKeys.newDataBlockKey) as? BlockContainer { return newDataBlock } return nil } set(newValue) { objc_setAssociatedObject(self, xy_associatedKeys.newDataBlockKey, newValue, .OBJC_ASSOCIATION_COPY_NONATOMIC) } } convenience init(collectionVewFlowLayout : UICollectionViewFlowLayout, originalDataBlock: @escaping XYRearrangeOriginaDataBlock, newDataBlock: @escaping XYRearrangeNewDataBlock) { self.init() let blockContainer: BlockContainer = BlockContainer() blockContainer.rearrangeNewDataBlock = newDataBlock blockContainer.rearrangeOriginaDataBlock = originalDataBlock self.newDataBlock = blockContainer }
“`
