jou指出的解决方案不支持值类型，这也适用于它们
包装纸
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)
}
}
}
}
这真的是一个很棒的解决方案，我想添加另一个使用示例，其中包括不是可选的结构和值。此外，可以简化 AssociatedKey 值。
struct Crate {
var name: String
}
class Box {
var name: String
init(name: String) {
self.name = name
}
}
extension UIViewController {
private struct AssociatedKey {
static var displayed: UInt8 = 0
static var box: UInt8 = 0
static var crate: UInt8 = 0
}
var displayed: Bool? {
get {
return getAssociatedObject(self, associativeKey: &AssociatedKey.displayed)
}
set {
if let value = newValue {
setAssociatedObject(self, value: value, associativeKey: &AssociatedKey.displayed, policy: objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
}
var box: Box {
get {
if let result:Box = getAssociatedObject(self, associativeKey: &AssociatedKey.box) {
return result
} else {
let result = Box(name: "")
self.box = result
return result
}
}
set {
setAssociatedObject(self, value: newValue, associativeKey: &AssociatedKey.box, policy: objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
var crate: Crate {
get {
if let result:Crate = getAssociatedObject(self, associativeKey: &AssociatedKey.crate) {
return result
} else {
let result = Crate(name: "")
self.crate = result
return result
}
}
set {
setAssociatedObject(self, value: newValue, associativeKey: &AssociatedKey.crate, policy: objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
}
}