Ios 如何在Swift中存储属性，与我在Objective-C中的存储方式相同？

我正在将一个应用程序从Objective-C切换到Swift，我有几个类别，其中包含存储属性，例如：

@interface UIView (MyCategory)

- (void)alignToView:(UIView *)view
          alignment:(UIViewRelativeAlignment)alignment;
- (UIView *)clone;

@property (strong) PFObject *xo;
@property (nonatomic) BOOL isAnimating;

@end

由于Swift扩展不接受这样的存储属性，我不知道如何维护与Objc代码相同的结构。存储属性对我的应用程序来说非常重要，我相信苹果一定已经为用Swift实现这一点创造了一些解决方案

正如jou所说，我所寻找的实际上是使用关联对象，所以我（在另一个上下文中）这样做了：

但在执行以下操作时，我会获得EXC\u BAD\u访问权限：

class UIBubble : UIView {
    required init(coder aDecoder: NSCoder) {
        ...
        self.layer.shapeLayer = CAShapeLayer()
        ...
    }
}

---

有什么想法吗？

您不能用新存储定义类别（Swift扩展）；必须计算而不是存储任何其他属性。该语法适用于Objective C，因为类别中的

@property

本质上意味着“我将提供getter和setter”。在Swift中，您需要自己定义这些属性以获得计算属性；比如：

extension String {
    public var Foo : String {
        get
        {
            return "Foo"
        }

        set
        {
            // What do you want to do here?
        }
    }
}

---

应该行得通。请记住，您不能在setter中存储新值，只能使用现有的可用类状态。

对于Obj-c类别，您只能添加方法，不能添加实例变量

在您的示例中，您使用@property作为添加getter和setter方法声明的快捷方式。您仍然需要实现这些方法

---

类似地，在Swift中，您可以添加使用扩展来添加实例方法、计算属性等，但不能添加存储属性。

与Objective-C中一样，您不能将存储属性添加到现有类中。如果您要扩展Objective-C类（

UIView

肯定是其中之一），您仍然可以使用来模拟存储的属性：

extension UIButton {

    struct Keys {
        static fileprivate var color: UInt8 = 0
        static fileprivate var index: UInt8 = 0
    }

    var color: UIColor {
        get {
            return associated(to: self, key: &Keys.color) { .green }
        }
        set {
            associate(to: self, key: &Keys.color, value: newValue)
        }
    }

    var index: Int {
        get {
            return associated(to: self, key: &Keys.index) { -1 }
        }
        set {
            associate(to: self, key: &Keys.index, value: newValue)
        }
    }

}

    let button = UIButton()
    print(button.color) // UIExtendedSRGBColorSpace 0 1 0 1 == green
    button.color = .black
    print(button.color) // UIExtendedGrayColorSpace 0 1 == black

    print(button.index) // -1
    button.index = 3
    print(button.index) // 3

适用于Swift 1

import ObjectiveC

private var xoAssociationKey: UInt8 = 0

extension UIView {
    var xo: PFObject! {
        get {
            return objc_getAssociatedObject(self, &xoAssociationKey) as? PFObject
        }
        set(newValue) {
            objc_setAssociatedObject(self, &xoAssociationKey, newValue, objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN))
        }
    }
}

关联键是一个指针，它对于每个关联都应该是唯一的。为此，我们创建一个私有全局变量，并使用

&

运算符将其内存地址用作键。有关如何在Swift中处理指针的更多详细信息，请参见

为Swift 2和Swift 3更新

import ObjectiveC

private var xoAssociationKey: UInt8 = 0

extension UIView {
    var xo: PFObject! {
        get {
            return objc_getAssociatedObject(self, &xoAssociationKey) as? PFObject
        }
        set(newValue) {
            objc_setAssociatedObject(self, &xoAssociationKey, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
        }
    }
}

为Swift 4更新

import CoreLocation

extension CLLocation {

    private struct AssociatedKeys {
        static var originAddress = "originAddress"
        static var destinationAddress = "destinationAddress"
    }

    var originAddress: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.originAddress) as? String
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(
                    self,
                    &AssociatedKeys.originAddress,
                    newValue as NSString?,
                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC
                )
            }
        }
    }

    var destinationAddress: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.destinationAddress) as? String
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(
                    self,
                    &AssociatedKeys.destinationAddress,
                    newValue as NSString?,
                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC
                )
            }
        }
    }

}

在Swift 4中，它要简单得多。Holder结构将包含我们的计算属性将向世界公开的私有值，从而产生存储属性行为的假象

---

jou指出的解决方案不支持值类型， 这也适用于他们

包装器

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
    }
}

这确实是一个非常好的解决方案，我想添加另一个使用示例，其中包括非可选的结构和值。此外，还可以简化关联的键值

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)
        }
    }
}

---

我更喜欢用纯Swift编写代码，而不是依赖Objective-C传统。因此，我编写了具有两个优点和两个缺点的纯Swift解决方案

优势：

纯Swift码

用于类和补全，或更具体地用于

任何
对象

缺点：

代码应该调用方法willDeinit（）来释放链接到特定类实例的对象，以避免内存泄漏

对于这个确切的示例，您不能直接对UIView进行扩展，因为

var frame

是对UIView的扩展，而不是类的一部分

编辑：

---

因此，我认为我找到了一种比上述方法更简洁的方法，因为它不需要任何全局变量。我从这里得到的：

要点是使用如下结构：

extension UIViewController {
    private struct AssociatedKeys {
        static var DescriptiveName = "nsh_DescriptiveName"
    }

    var descriptiveName: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.DescriptiveName) as? String
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(
                    self,
                    &AssociatedKeys.DescriptiveName,
                    newValue as NSString?,
                    UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC)
                )
            }
        }
    }
}

Swift 2的更新

private struct AssociatedKeys {
    static var displayed = "displayed"
}

//this lets us check to see if the item is supposed to be displayed or not
var displayed : Bool {
    get {
        guard let number = objc_getAssociatedObject(self, &AssociatedKeys.displayed) as? NSNumber else {
            return true
        }
        return number.boolValue
    }

    set(value) {
        objc_setAssociatedObject(self,&AssociatedKeys.displayed,NSNumber(bool: value),objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    }
}

---

我的薪水是0.02美元。此代码是用Swift 2.0编写的

extension CALayer {
    private struct AssociatedKeys {
        static var shapeLayer:CAShapeLayer?
    }

    var shapeLayer: CAShapeLayer? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.shapeLayer) as? CAShapeLayer
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(self, &AssociatedKeys.shapeLayer, newValue as CAShapeLayer?, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            }
        }
    }
}

---

我尝试了许多解决方案，发现这是使用额外变量参数实际扩展类的唯一方法。

我还遇到了EXC\u BAD\u访问问题。

objc\u getAssociatedObject（）

和

objc\u setAssociatedObject（）

中的值应该是一个对象。

objc\u AssociationPolicy

应该与对象匹配。

我尝试使用这里的一些答案中提到的objc\u setassociated对象，但在失败了几次之后，我退了一步，意识到我没有理由需要它。借用这里的一些想法，我提出了这段代码，它简单地存储了一个数组，其中包含我的额外数据（在本例中为MyClass），这些数据由我想要关联的对象索引：

class MyClass {
    var a = 1
    init(a: Int)
    {
        self.a = a
    }
}

extension UIView
{
    static var extraData = [UIView: MyClass]()

    var myClassData: MyClass? {
        get {
            return UIView.extraData[self]
        }
        set(value) {
            UIView.extraData[self] = value
        }
    }
}

// Test Code: (Ran in a Swift Playground)
var view1 = UIView()
var view2 = UIView()

view1.myClassData = MyClass(a: 1)
view2.myClassData = MyClass(a: 2)
print(view1.myClassData?.a)
print(view2.myClassData?.a)

---

我试图使用objc_getAssociatedObject、objc_setAssociatedObject来存储属性，但没有任何运气。我的目标是为UITextField创建扩展，以验证文本输入字符的长度。 下面的代码对我来说很好。希望这能帮助别人

private var _min: Int?
private var _max: Int?

extension UITextField {    
    @IBInspectable var minLength: Int {
        get {
            return _min ?? 0
        }
        set {
            _min = newValue
        }
    }

    @IBInspectable var maxLength: Int {
        get {
            return _max ?? 1000
        }
        set {
            _max = newValue
        }
    }

    func validation() -> (valid: Bool, error: String) {
        var valid: Bool = true
        var error: String = ""
        guard let text = self.text else { return (true, "") }

        if text.characters.count < minLength {
            valid = false
            error = "Textfield should contain at least \(minLength) characters"
        }

        if text.characters.count > maxLength {
            valid = false
            error = "Textfield should not contain more then \(maxLength) characters"
        }

        if (text.characters.count < minLength) && (text.characters.count > maxLength) {
            valid = false
            error = "Textfield should contain at least \(minLength) characters\n"
            error = "Textfield should not contain more then \(maxLength) characters"
        }

        return (valid, error)
    }
}

private var\u min:Int？
私有变量max:Int？
扩展UITextField{
@IBInspectable变量minLength:Int{
得到{
返回最小值？？0
}
设置{
_最小值=新值
}
}
@IBInspectable变量maxLength:Int{
得到{
返回最大值为1000
}
设置{
_最大值=新值
}
}
func validation（）->（有效：Bool，错误：String）{
var-valid:Bool=true
变量错误：String=“”
guard let text=self.text else{return（true，“”）}
如果text.characters.count<最小长度{
有效=错误
error=“Textfield应至少包含\（minLength）个字符”
}
如果text.characters.count>maxLength{
有效=错误
error=“Textfield不应包含超过\（maxLength）个字符”
}
if（text.characters.countmaxLength）{
有效=错误
error=“Textfield应至少包含\（minLength）个字符\n”
error=“Textfield不应包含超过\（maxLength）个字符”
}
返回（有效，错误）
}
}

我发现这个解决方案更实用

更新为Swift 3

…然后在你的代码中

class gameController: UIViewController {

    @IBOutlet var game: gameClass!

    override func viewDidLoad() {
        self.view.backgroundColor = UIColor.graySpace

    }
}

这是simplif

extension UIColor {

    static let graySpace = UIColor.init(red: 50/255, green: 50/255, blue: 50/255, alpha: 1.0)
    static let redBlood = UIColor.init(red: 102/255, green: 0/255, blue: 0/255, alpha: 1.0)
    static let redOrange = UIColor.init(red: 204/255, green: 17/255, blue: 0/255, alpha: 1.0)

    func alpha(value : CGFloat) -> UIColor {
        var r = CGFloat(0), g = CGFloat(0), b = CGFloat(0), a = CGFloat(0)
        self.getRed(&r, green: &g, blue: &b, alpha: &a)
        return UIColor(red: r, green: g, blue: b, alpha: value)
    }

}

class gameController: UIViewController {

    @IBOutlet var game: gameClass!

    override func viewDidLoad() {
        self.view.backgroundColor = UIColor.graySpace

    }
}

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 associated<T>(to base: AnyObject,
                key: UnsafePointer<UInt8>,
                policy: objc_AssociationPolicy = .OBJC_ASSOCIATION_RETAIN,
                initialiser: () -> T) -> T {
    if let v = objc_getAssociatedObject(base, key) as? T {
        return v
    }

    if let v = objc_getAssociatedObject(base, key) as? Lifted<T> {
        return v.value
    }

    let lifted = Lifted(initialiser())
    objc_setAssociatedObject(base, key, lifted, policy)
    return lifted.value
}

func associate<T>(to base: AnyObject, key: UnsafePointer<UInt8>, value: T, policy: objc_AssociationPolicy = .OBJC_ASSOCIATION_RETAIN) {
    if let v: AnyObject = value as AnyObject? {
        objc_setAssociatedObject(base, key, v, policy)
    }
    else {
        objc_setAssociatedObject(base, key, lift(value), policy)
    }
}

extension UIButton {

    struct Keys {
        static fileprivate var color: UInt8 = 0
        static fileprivate var index: UInt8 = 0
    }

    var color: UIColor {
        get {
            return associated(to: self, key: &Keys.color) { .green }
        }
        set {
            associate(to: self, key: &Keys.color, value: newValue)
        }
    }

    var index: Int {
        get {
            return associated(to: self, key: &Keys.index) { -1 }
        }
        set {
            associate(to: self, key: &Keys.index, value: newValue)
        }
    }

}

    let button = UIButton()
    print(button.color) // UIExtendedSRGBColorSpace 0 1 0 1 == green
    button.color = .black
    print(button.color) // UIExtendedGrayColorSpace 0 1 == black

    print(button.index) // -1
    button.index = 3
    print(button.index) // 3

public final class ObjectAssociation<T: AnyObject> {

    private let policy: objc_AssociationPolicy

    /// - Parameter policy: An association policy that will be used when linking objects.
    public init(policy: objc_AssociationPolicy = .OBJC_ASSOCIATION_RETAIN_NONATOMIC) {

        self.policy = policy
    }

    /// Accesses associated object.
    /// - Parameter index: An object whose associated object is to be accessed.
    public subscript(index: AnyObject) -> T? {

        get { return objc_getAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque()) as! T? }
        set { objc_setAssociatedObject(index, Unmanaged.passUnretained(self).toOpaque(), newValue, policy) }
    }
}

extension SomeType {

    private static let association = ObjectAssociation<NSObject>()

    var simulatedProperty: NSObject? {

        get { return SomeType.association[self] }
        set { SomeType.association[self] = newValue }
    }
}

extension CALayer {

    private static let initialPathAssociation = ObjectAssociation<CGPath>()
    private static let shapeLayerAssociation = ObjectAssociation<CAShapeLayer>()

    var initialPath: CGPath! {
        get { return CALayer.initialPathAssociation[self] }
        set { CALayer.initialPathAssociation[self] = newValue }
    }

    var shapeLayer: CAShapeLayer? {
        get { return CALayer.shapeLayerAssociation[self] }
        set { CALayer.shapeLayerAssociation[self] = newValue }
    }
}

public final class Storage : AnyObject {

    var object:Any?

    public init(_ object:Any) {
        self.object = object
    }
}

extension Date {

    private static let associationMap = NSMapTable<NSString, AnyObject>()
    private struct Keys {
        static var Locale:NSString = "locale"
    }

    public var locale:Locale? {
        get {

            if let storage = Date.associationMap.object(forKey: Keys.Locale) {
                return (storage as! Storage).object as? Locale
            }
            return nil
        }
        set {
            if newValue != nil {
                Date.associationMap.setObject(Storage(newValue), forKey: Keys.Locale)
            }
        }
    }
}



var date = Date()
date.locale = Locale(identifier: "pt_BR")
print( date.locale )

import CoreLocation

extension CLLocation {

    private struct AssociatedKeys {
        static var originAddress = "originAddress"
        static var destinationAddress = "destinationAddress"
    }

    var originAddress: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.originAddress) as? String
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(
                    self,
                    &AssociatedKeys.originAddress,
                    newValue as NSString?,
                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC
                )
            }
        }
    }

    var destinationAddress: String? {
        get {
            return objc_getAssociatedObject(self, &AssociatedKeys.destinationAddress) as? String
        }
        set {
            if let newValue = newValue {
                objc_setAssociatedObject(
                    self,
                    &AssociatedKeys.destinationAddress,
                    newValue as NSString?,
                    .OBJC_ASSOCIATION_RETAIN_NONATOMIC
                )
            }
        }
    }

}

extension UIViewController {
    private static var _myComputedProperty = [String:Bool]()

    var myComputedProperty:Bool {
        get {
            let tmpAddress = String(format: "%p", unsafeBitCast(self, to: Int.self))
            return UIViewController._myComputedProperty[tmpAddress] ?? false
        }
        set(newValue) {
            let tmpAddress = String(format: "%p", unsafeBitCast(self, to: Int.self))
            UIViewController._myComputedProperty[tmpAddress] = newValue
        }
    }
}

extension UIView {

    func setStringValue(value: String, key: String) {
        layer.setValue(value, forKey: key)
    }

    func stringValueFor(key: String) -> String? {
        return layer.value(forKey: key) as? String
    }
}

let key = "COLOR"

let redView = UIView() 

// To set
redView.setStringAttribute(value: "Red", key: key)

// To read
print(redView.stringValueFor(key: key)) // Optional("Red")

extension UIView {
    
    struct Holder {
        static var _padding:[UIView:UIEdgeInsets] = [:]
    }
   
    var padding : UIEdgeInsets {
        get{ return UIView.Holder._padding[self] ?? .zero}
        set { UIView.Holder._padding[self] = newValue }
    }

}

import Foundation
import UIKit

extension CustomView {
    
    // can make private
    static let storedProperties = WeakDictionary<UIView, Properties>()
    
    struct Properties {
        var url: String = ""
        var status = false
        var desc: String { "url: \(url), status: \(status)" }
    }
    
    var properties: Properties {
        get {
            return CustomView.storedProperties.get(forKey: self) ?? Properties()
        }
        set {
            CustomView.storedProperties.set(forKey: self, object: newValue)
        }
    }
}

var view: CustomView? = CustomView()
print("1 print", view?.properties.desc ?? "nil")
view?.properties.url = "abc"
view?.properties.status = true
print("2 print", view?.properties.desc ?? "nil")
view = nil

import Foundation

private class WeakHolder<T: AnyObject>: Hashable {
    weak var object: T?
    let hash: Int

    init(object: T) {
        self.object = object
        hash = ObjectIdentifier(object).hashValue
    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(hash)
    }

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

class WeakDictionary<T1: AnyObject, T2> {
    private var dictionary = [WeakHolder<T1>: T2]()

    func set(forKey: T1, object: T2?) {
        dictionary[WeakHolder(object: forKey)] = object
    }

    func get(forKey: T1) -> T2? {
        let obj = dictionary[WeakHolder(object: forKey)]
        return obj
    }

    func forEach(_ handler: ((key: T1, value: T2)) -> Void) {
        dictionary.forEach {
            if let object = $0.key.object, let value = dictionary[$0.key] {
                handler((object, value))
            }
        }
    }
    
    func clean() {
        var removeList = [WeakHolder<T1>]()
        dictionary.forEach {
            if $0.key.object == nil {
                removeList.append($0.key)
            }
        }
        removeList.forEach {
            dictionary[$0] = nil
        }
    }
}