如何在Swift中声明一个弱引用数组？-Java 学习之路

160

我想在Swift中存储一组弱引用 . 数组本身不应该是弱引用 - 它的元素应该是 . 我认为Cocoa NSPointerArray 提供了非类型安全版本 .

15 回答

10
创建一个通用包装器：
```
class Weak<T: AnyObject> {
  weak var value : T?
  init (value: T) {
    self.value = value
  }
}
```
将此类的实例添加到您的数组 .
```
class Stuff {}
var weakly : [Weak<Stuff>] = [Weak(value: Stuff()), Weak(value: Stuff())]
```
定义 Weak 时，您可以使用 struct 或 class .

此外，为了帮助获取数组内容，您可以执行以下操作：
```
extension Array where Element:Weak<AnyObject> {
  mutating func reap () {
    self = self.filter { nil != $0.value }
  }
}
```
上面的 AnyObject 的使用应该用 T 替换 - 但我不认为当前的Swift语言允许扩展定义为这样 .
回复于 2024-04-24T10:48:58+08:00
9

您可以将NSHashTable与weakObjectsHashTable一起使用 . NSHashTable.weakObjectsHashTable()

对于Swift 3： NSHashTable.weakObjects()

NSHashTable Class Reference

在OS X v10.5及更高版本中可用 . 适用于iOS 6.0及更高版本 .

回复于 2024-04-24T10:48:58+08:00
134
This is not my solution. I found it on the Apple Developer Forums.

@GoZoner有一个很好的答案，但它崩溃了Swift编译器 .

这是一个弱对象容器的版本不会崩溃当前发布的编译器 .
```
struct WeakContainer<T where T: AnyObject> {
    weak var _value : T?

    init (value: T) {
        _value = value
    }

    func get() -> T? {
        return _value
    }
}
```
然后，您可以创建这些容器的数组：
```
let myArray: Array<WeakContainer<MyClass>> = [myObject1, myObject2]
```
回复于 2024-04-24T10:48:58+08:00

派对有点迟，但试试我的 . 我实现为Set而不是数组 .

WeakObjectSet

class WeakObject<T: AnyObject>: Equatable, Hashable {
    weak var object: T?
    init(object: T) {
        self.object = object
    }

    var hashValue: Int {
        if let object = self.object { return unsafeAddressOf(object).hashValue }
        else { return 0 }
    }
}

func == <T> (lhs: WeakObject<T>, rhs: WeakObject<T>) -> Bool {
    return lhs.object === rhs.object
}


class WeakObjectSet<T: AnyObject> {
    var objects: Set<WeakObject<T>>

    init() {
        self.objects = Set<WeakObject<T>>([])
    }

    init(objects: [T]) {
        self.objects = Set<WeakObject<T>>(objects.map { WeakObject(object: $0) })
    }

    var allObjects: [T] {
        return objects.flatMap { $0.object }
    }

    func contains(object: T) -> Bool {
        return self.objects.contains(WeakObject(object: object))
    }

    func addObject(object: T) {
        self.objects.unionInPlace([WeakObject(object: object)])
    }

    func addObjects(objects: [T]) {
        self.objects.unionInPlace(objects.map { WeakObject(object: $0) })
    }
}

用法

var alice: NSString? = "Alice"
var bob: NSString? = "Bob"
var cathline: NSString? = "Cathline"

var persons = WeakObjectSet<NSString>()
persons.addObject(bob!)
print(persons.allObjects) // [Bob]

persons.addObject(bob!)
print(persons.allObjects) // [Bob]

persons.addObjects([alice!, cathline!])
print(persons.allObjects) // [Alice, Cathline, Bob]

alice = nil
print(persons.allObjects) // [Cathline, Bob]

bob = nil
print(persons.allObjects) // [Cathline]

请注意WeakObjectSet不会采用String类型而是采用NSString . 因为，String类型不是AnyType . 我的快速版本是 Apple Swift version 2.2 (swiftlang-703.0.18.1 clang-703.0.29) .

代码可以从Gist中获取 . https://gist.github.com/codelynx/30d3c42a833321f17d39

**于2010年11月上市

我将代码更新为Swift 4

// Swift 4, Xcode Version 9.1 (9B55)

class WeakObject<T: AnyObject>: Equatable, Hashable {
    weak var object: T?
    init(object: T) {
        self.object = object
    }

    var hashValue: Int {
        if var object = object { return UnsafeMutablePointer<T>(&object).hashValue }
        return 0
    }

    static func == (lhs: WeakObject<T>, rhs: WeakObject<T>) -> Bool {
        return lhs.object === rhs.object
    }
}

class WeakObjectSet<T: AnyObject> {
    var objects: Set<WeakObject<T>>

    init() {
        self.objects = Set<WeakObject<T>>([])
    }

    init(objects: [T]) {
        self.objects = Set<WeakObject<T>>(objects.map { WeakObject(object: $0) })
    }

    var allObjects: [T] {
        return objects.flatMap { $0.object }
    }

    func contains(_ object: T) -> Bool {
        return self.objects.contains(WeakObject(object: object))
    }

    func addObject(_ object: T) {
        self.objects.formUnion([WeakObject(object: object)])
    }

    func addObjects(_ objects: [T]) {
        self.objects.formUnion(objects.map { WeakObject(object: $0) })
    }
}

正如gokeji所提到的，我发现NSString不会根据使用中的代码取消分配 . 我摸不着头脑，按照以下方式写了MyString类 .

// typealias MyString = NSString
class MyString: CustomStringConvertible {
    var string: String
    init(string: String) {
        self.string = string
    }
    deinit {
        print("relasing: \(string)")
    }
    var description: String {
        return self.string
    }
}

然后像这样用 MyString 替换 NSString . 然后奇怪地说它有效 .

var alice: MyString? = MyString(string: "Alice")
var bob: MyString? = MyString(string: "Bob")
var cathline: MyString? = MyString(string: "Cathline")

var persons = WeakObjectSet<MyString>()

persons.addObject(bob!)
print(persons.allObjects) // [Bob]

persons.addObject(bob!)
print(persons.allObjects) // [Bob]

persons.addObjects([alice!, cathline!])
print(persons.allObjects) // [Alice, Cathline, Bob]

alice = nil
print(persons.allObjects) // [Cathline, Bob]

bob = nil
print(persons.allObjects) // [Cathline]

然后我发现一个奇怪的页面可能与此问题有关 .

弱参考保留解除分配的NSString（仅限XC9 iOS Sim）

https://bugs.swift.org/browse/SR-5511

它说问题是 RESOLVED ，但我想知道这是否仍然与这个问题有关 . 无论如何，MyString或NSString之间的行为差异超出了这个范围，但如果有人想出这个问题，我将不胜感激 .

回复于 2024-04-24T10:48:58+08:00

您可以通过创建包装器对象来保存弱指针来完成此操作 .

struct WeakThing<T: AnyObject> {
  weak var value: T?
  init (value: T) {
    self.value = value
  }
}

然后在阵列中使用这些

var weakThings = WeakThing<Foo>[]()

回复于 2024-04-24T10:48:58+08:00

我有同样的想法用泛型创建弱容器 .
结果我为 NSHashTable 创建了包装器：

class WeakSet<ObjectType>: SequenceType {

    var count: Int {
        return weakStorage.count
    }

    private let weakStorage = NSHashTable.weakObjectsHashTable()

    func addObject(object: ObjectType) {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        weakStorage.addObject(object as? AnyObject)
    }

    func removeObject(object: ObjectType) {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        weakStorage.removeObject(object as? AnyObject)
    }

    func removeAllObjects() {
        weakStorage.removeAllObjects()
    }

    func containsObject(object: ObjectType) -> Bool {
        guard object is AnyObject else { fatalError("Object (\(object)) should be subclass of AnyObject") }
        return weakStorage.containsObject(object as? AnyObject)
    }

    func generate() -> AnyGenerator<ObjectType> {
        let enumerator = weakStorage.objectEnumerator()
        return anyGenerator {
            return enumerator.nextObject() as! ObjectType?
        }
    }
}

用法：

protocol MyDelegate : AnyObject {
    func doWork()
}

class MyClass: AnyObject, MyDelegate {
    fun doWork() {
        // Do delegated work.
    }
}

var delegates = WeakSet<MyDelegate>()
delegates.addObject(MyClass())

for delegate in delegates {
    delegate.doWork()
}

这不是最好的解决方案，因为 WeakSet 可以用任何类型初始化，如果这种类型不符合 AnyObject 协议，那么应用程序将崩溃，原因很详细 . 但我现在没有看到任何更好的解决方案 .

原始解决方案是以这种方式定义 WeakSet ：

class WeakSet<ObjectType: AnyObject>: SequenceType {}

但在这种情况下 WeakSet 无法使用协议进行初始化：

protocol MyDelegate : AnyObject {
    func doWork()
}

let weakSet = WeakSet<MyDelegate>()

目前上面的代码无法编译（Swift 2.1，Xcode 7.1） .
这就是为什么我放弃符合 AnyObject 并添加额外的警卫 fatalError() 断言 .

回复于 2024-04-24T10:48:58+08:00

功能样式包装怎么样？

class Class1 {}

func captureWeakly<T> (_ target:T) -> (() -> T?) where T: AnyObject {
    return { [weak target] in
        return target
    }
}

let obj1 = Class1()
let obj2 = Class1()
let obj3 = Class1()
let captured1 = captureWeakly(obj1)
let captured2 = captureWeakly(obj2)
let captured3 = captureWeakly(obj3)

只需调用返回的闭包来检查目标是否仍然存活 .

let isAlive = captured1() != nil
let theValue = captured1()!

您可以将此闭包存储到数组中 .

let array1 = Array<() -> (Class1?)>([captured1, captured2, captured3])

并且您可以通过映射调用闭包来检索弱捕获的值 .

let values = Array(array1.map({ $0() }))

回复于 2024-04-24T10:48:58+08:00

WeakContainer的现有示例很有用，但它并没有真正帮助在现有的swift容器（如Lists和Dictionaries）中使用弱引用 .

如果要使用List等方法，那么WeakContainer将需要实现Equatable . 所以我添加了代码以允许WeakContainer相等 .

如果你想在字典中使用WeakContainer，我也使它可以使用它，因此它可以用作字典键 .

我还将它重命名为WeakObject，强调这仅适用于类类型，并将其与WeakContainer示例区分开来：

struct WeakObject<TYPE where TYPE:AnyObject> : Equatable, Hashable
{
    weak var _value : TYPE?
    let _originalHashValue : Int

    init (value: TYPE)
    {
        _value = value

        // We keep around the original hash value so that we can return it to represent this
        // object even if the value became Nil out from under us because the object went away.
        _originalHashValue = ObjectIdentifier(value).hashValue
    }

    var value : TYPE?
    {
        return _value
    }

    var hashValue: Int
    {
        return _originalHashValue
    }
}

func ==<T>(lhs: WeakObject<T>, rhs: WeakObject<T>) -> Bool
{
    if lhs.value == nil  &&  rhs.value == nil {
        return true
    }
    else if lhs.value == nil  ||  rhs.value == nil {
        return false
    }

    // If the objects are the same, then we are good to go
    return lhs.value! === rhs.value!
}

这允许你做一些很酷的东西，比如使用弱引用词典：

private var m_observerDict : Dictionary<WeakObject<AnyObject>,FLObservationBlock> = Dictionary()

func addObserver( observer:AnyObject, block:FLObservationBlock )
{
    let weakObserver = WeakObject(value:observer)
    m_observerDict[weakObserver] = block
}


func removeObserver( observer:AnyObject )
{
    let weakObserver = WeakObject(value:observer)
    m_observerDict.removeValueForKey(weakObserver)
}

回复于 2024-04-24T10:48:58+08:00

这里's how to make @GoZoner'的答案很符合 Hashable ，因此它可以在Container对象中编入索引，例如： Set ， Dictionary ， Array 等 .

private class Weak<T: AnyObject>: Hashable {
    weak var value : T!
    init (value: T) {
       self.value = value
    }

    var hashValue : Int {
       // ObjectIdentifier creates a unique hashvalue for objects.
       return ObjectIdentifier(self.value).hashValue
    }
}

// Need to override so we can conform to Equitable.
private func == <T>(lhs: Weak<T>, rhs: Weak<T>) -> Bool {
    return lhs.hashValue == rhs.hashValue
}

回复于 2024-04-24T10:48:58+08:00

基于Kaz Yoshikawa的回答

详情

xCode 9.1，Swift 4

解决方案

WeakObject

import Foundation

protocol WeakObjectProtocol {
    associatedtype WeakObjectType
    var value: WeakObjectType? {get set}
    init(object: WeakObjectType)
}

class WeakObject<T: AnyObject>: WeakObjectProtocol {
    typealias WeakObjectType = T
    weak var value: WeakObjectType?

    required init(object: WeakObjectType) {
        self.value = object
    }

    var referenceCount: Int {
        return CFGetRetainCount(value)
    }
}

extension WeakObject: Equatable {
    static func == (lhs: WeakObject<T>, rhs: WeakObject<T>) -> Bool {
        return lhs.value === rhs.value
    }
}

extension WeakObject: Hashable {
    var hashValue: Int {
        if var value = value { return UnsafeMutablePointer<T>(&value).hashValue }
        return 0
    }
}

extension WeakObject: CustomStringConvertible {

    var description: String {
        if let value = value  {
            let className = String(describing: type(of: value.self))
            return "{class: \(className); referenceCount: \(referenceCount)}"
        }
        return "nil"
    }
}

扩展阵列

import Foundation

extension Array where Element: AnyObject  {

    var weak: Array<WeakObject<Element>> {
        var weakArray = [WeakObject<Element>]()
        for item in self {
            let obj = WeakObject(object: item)
            weakArray.append(obj)
        }
        return weakArray
    }
}

extension Array where Element: WeakObjectProtocol {

    typealias EnumeratedWeakObjectClosure = (_ index: Int, _ value: Element.WeakObjectType?)->()
    typealias WeakObjectClosure = (_ value: Element.WeakObjectType?)->()

    mutating func removeNils() {
        self = self.flatMap{ (element) -> Element? in
            if element.value == nil {
                return nil
            }
            return element
        }
    }

    mutating func append(weakValue: Element.WeakObjectType) {
        append(Element(object: weakValue))
    }

    subscript(index: Int) -> Element.WeakObjectType? {
        get {
            return self[index].value
        }
    }

    func `for` (closure: WeakObjectClosure){
        for item in self {
            closure(item.value)
        }
    }

    func forEnumerated (closure: EnumeratedWeakObjectClosure) {
        for (index,item) in self.enumerated() {
            closure(index, item.value)
        }
    }

    mutating func remove(index: Int, closure: EnumeratedWeakObjectClosure) {
        closure(index, self[index].value)
        remove(at: index)
    }

    mutating func remove(index: Int, closure: WeakObjectClosure) {
        closure(self[index].value)
        remove(at: index)
    }
}

用法

// Array of week objects
var weakArray = [WeakObject<UIView>]()

// Get array of week objects (transfom from [AnyObject])
// way 1
weakArray = view.subviews.weak
// way 2
weakArray = [view.subviews[0], view.subviews[1]].weak

// Add single element to the end of the array
weakArray.append(weakValue: UIView())

// For loop
weakArray.for { (element) in
    print("\(String(describing: element))")
}

// For loop with index (position number)
weakArray.forEnumerated { (index, element) in
    print("\(index) \(String(describing: element))")
}

完整样本

不要忘记在此处添加解决方案代码

ViewController

import UIKit

class ViewController: UIViewController {

    var weakArray = [WeakObject<UIView>]()
    override func viewDidLoad() {
        super.viewDidLoad()
        addSubviews()

        weakArray = view.subviews.weak
        weakArray.append(weakValue: generateView())
        weakArray.remove(index: 0) { item in
            item?.removeFromSuperview()
        }
        weakArray.for { (element) in
            print("\(String(describing: element))")
        }

    }

    func printArray(title: String) {

        print("=============================\n\(title)\ncount: \(weakArray.count)")
        weakArray.forEnumerated { (index,element) in
            print("\(index) \(String(describing: element))")
        }
    }
}

// Creating views

extension ViewController {

    func generateView() -> UIView {
        let randomValue: ()->(CGFloat) = { return CGFloat(rand[50, 300]) }
        let view = UIView(frame: CGRect(x: randomValue(), y: randomValue(), width: randomValue(), height: randomValue()))
        view.backgroundColor = .blue
        let randomColorComponent: ()->(CGFloat) = { return CGFloat(rand[0, 255])/CGFloat(255) }
        let color = UIColor(red: randomColorComponent(), green: randomColorComponent(), blue: randomColorComponent(), alpha: 1)
        view.backgroundColor = color
        self.view.addSubview(view)
        return view
    }

    func addSubviews() {

        _ = generateView()
        _ = generateView()

        addButtons()
    }
}

// Buttons

extension ViewController {

    func addButtons() {
        var button = UIButton(frame: CGRect(x: 10, y: 20, width: 40, height: 40))
        button.setTitle("Add", for: .normal)
        button.addTarget(self, action: #selector(addView), for: .touchUpInside)
        button.setTitleColor(.blue, for: .normal)
        view.addSubview(button)

        button = UIButton(frame: CGRect(x: 60, y: 20, width: 60, height: 40))
        button.setTitle("Delete", for: .normal)
        button.addTarget(self, action: #selector(deleteView), for: .touchUpInside)
        button.setTitleColor(.blue, for: .normal)
        view.addSubview(button)

        button = UIButton(frame: CGRect(x: 120, y: 20, width: 100, height: 40))
        button.setTitle("Remove nil", for: .normal)
        button.addTarget(self, action: #selector(removeNils), for: .touchUpInside)
        button.setTitleColor(.blue, for: .normal)
        view.addSubview(button)
    }

    @objc func deleteView() {
        view.subviews.filter { view -> Bool in
            return !(view is UIButton)
            }.first?.removeFromSuperview()

        DispatchQueue.main.async {
            self.view.layoutIfNeeded()
            self.printArray(title: "First view deleted")
        }
    }

    @objc func addView() {
        weakArray.append(weakValue: generateView())
        printArray(title: "View addded")
    }

    @objc func removeNils() {
        weakArray.removeNils()
        printArray(title: "Remove all nil elements in weakArray")
    }
}

兰德功能

class Random {

    subscript<T>(_ min: T, _ max: T) -> T where T : BinaryInteger {
        get {
            return rand(min-1, max+1)
        }
    }
}

let rand = Random()

func rand<T>(_ min: T, _ max: T) -> T where T : BinaryInteger {
    let _min = min + 1
    let difference = max - _min
    return T(arc4random_uniform(UInt32(difference))) + _min
}

结果

enter image description here

回复于 2024-04-24T10:48:58+08:00

其他答案涵盖了泛型角度 . 以为我会分享一些涵盖 nil 角度的简单代码 .

我想要一个当前存在于应用程序中的所有 Label 的静态数组（偶尔读取），但是我不想看到 nil 以前的旧数据库 .

没什么好看的，这是我的代码......

public struct WeakLabel {
    public weak var label : Label?
    public init(_ label: Label?) {
        self.label = label
    }
}

public class Label : UILabel {
    static var _allLabels = [WeakLabel]()
    public static var allLabels:[WeakLabel] {
        get {
            _allLabels = _allLabels.filter{$0.label != nil}
            return _allLabels.filter{$0.label != nil}.map{$0.label!}
        }
    }
    public required init?(coder: NSCoder) {
        super.init(coder: coder)
        Label._allLabels.append(WeakLabel(self))
    }
    public override init(frame: CGRect) {
        super.init(frame: frame)
        Label._allLabels.append(WeakLabel(self))
    }
}

回复于 2024-04-24T10:48:58+08:00

针对同一问题的又一个解决方案......这个问题的重点是存储对象的弱引用，但也允许存储结构 .

[我不确定它有多有用，但确实需要一段时间才能使语法正确]

class WeakWrapper : Equatable {
    var valueAny : Any?
    weak var value : AnyObject?

    init(value: Any) {
        if let valueObj = value as? AnyObject {
            self.value = valueObj
        } else {
            self.valueAny = value
        }
    }

    func recall() -> Any? {
        if let value = value {
            return value
        } else if let value = valueAny {
            return value
        }
        return nil
    }
}


func ==(lhs: WeakWrapper, rhs: WeakWrapper) -> Bool {
    return ObjectIdentifier(lhs) == ObjectIdentifier(rhs)
}



class Stuff {}
var weakArray : [WeakWrapper] = [WeakWrapper(value: Stuff()), WeakWrapper(value: CGRectZero)]

extension Array where Element : WeakWrapper  {

    mutating func removeObject(object: Element) {
        if let index = self.indexOf(object) {
            self.removeAtIndex(index)
        }
    }

    mutating func compress() {
        for obj in self {
            if obj.recall() == nil {
                self.removeObject(obj)
            }
        }
    }


}

weakArray[0].recall()
weakArray[1].recall() == nil
weakArray.compress()
weakArray.count

回复于 2024-04-24T10:48:58+08:00

1

你可以在 Array 周围创建包装器 . 或使用此库https://github.com/NickRybalko/WeakPointerArray let array = WeakPointerArray<AnyObject>() 这是类型安全的 .

回复于 2024-04-24T10:48:58+08:00

我基于@Eonil的工作，因为我喜欢闭包弱绑定策略，但我不想使用函数运算符来变量，因为它感觉非常反直觉

相反，我所做的如下：

class Weak<T> where T: AnyObject {
    fileprivate var storedWeakReference: ()->T? = { return nil }

    var value: T? {
        get {
            return storedWeakReference()
        }
    }

    init(_ object: T) {
        self.storedWeakReference = storeWeakReference(object)
    }

    fileprivate func storeWeakReference<T> (_ target:T) -> ()->T? where T: AnyObject {
        return { [weak target] in
            return target
        }
    }
}

通过这种方式，您可以执行以下操作：

var a: UIViewController? = UIViewController()
let b = Weak(a)
print(a) //prints Optional(<UIViewController: 0xSomeAddress>)
print(b.value) //prints Optional(<UIViewController: 0xSomeAddress>)
a = nil
print(a) //prints nil
print(b.value) //prints nil

回复于 2024-04-24T10:48:58+08:00

由于 NSPointerArray 已经自动处理了大部分内容，因此我通过为其设置类型安全包装来解决问题，这避免了其他答案中的许多样板：

class WeakArray<T: AnyObject> {
    private let pointers = NSPointerArray.weakObjects()

    init (_ elements: T...) {
        elements.forEach{self.pointers.addPointer(Unmanaged.passUnretained($0).toOpaque())}
    }

    func get (_ index: Int) -> T? {
        if index < self.pointers.count, let pointer = self.pointers.pointer(at: 0) {
            return Unmanaged<T>.fromOpaque(pointer).takeUnretainedValue()
        } else {
            return nil
        }
    }
    func append (_ element: T) {
        self.pointers.addPointer(Unmanaged.passUnretained(element).toOpaque())
    }
    func forEach (_ callback: (T) -> ()) {
        for i in 0..<self.pointers.count {
            if let element = self.get(i) {
                callback(element)
            }
        }
    }
    // implement other functionality as needed
}

用法示例：

class Foo {}
var foo: Foo? = Foo()
let array = WeakArray(foo!)
print(array.get(0)) // Optional(Foo)
foo = nil
DispatchQueue.main.async{print(array.get(0))} // nil

它预先做的更多，但在其余代码中的使用更加清晰IMO . 如果你想让它更像数组，你甚至可以实现下标，使它成为 SequenceType 等（但我的项目只需要 append 和 forEach 所以我手头没有确切的代码） .

回复于 2024-04-24T10:48:58+08:00

如何在Swift中声明一个弱引用数组？

15 回答

WeakObjectSet

用法

详情

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