函数式编程方法

不需要额外的课程。

简单地定义一个闭包数组()-> Foo?并使用[weak foo]将foo实例捕获为弱实例。

let foo = Foo()

var foos = [() -> Foo?]()
foos.append({ [weak foo] in return foo })

foos.forEach { $0()?.doSomething() }

细节

Swift 5.1, Xcode 11.3.1

解决方案

struct WeakObject<Object: AnyObject> { weak var object: Object? }

选项1

@propertyWrapper
struct WeakElements<Collect, Element> where Collect: RangeReplaceableCollection, Collect.Element == Optional<Element>, Element: AnyObject {
    private var weakObjects = [WeakObject<Element>]()

    init(wrappedValue value: Collect) { save(collection: value) }

    private mutating func save(collection: Collect) {
        weakObjects = collection.map { WeakObject(object: $0) }
    }

    var wrappedValue: Collect {
        get { Collect(weakObjects.map { $0.object }) }
        set (newValues) { save(collection: newValues) }
    }
}

选项1用法

class Class1 { // or struct
    @WeakElements var weakObjectsArray = [UIView?]() // Use like regular array. With any objects

    func test() {
        weakObjectsArray.append(UIView())
        weakObjectsArray.forEach { print($0) }
    }
}

选项2

struct WeakObjectsArray<Object> where Object: AnyObject {
    private var weakObjects = [WeakObject<Object>]()
}

extension WeakObjectsArray {
    typealias SubSequence = WeakObjectsArray<Object>
    typealias Element = Optional<Object>
    typealias Index = Int
    var startIndex: Index { weakObjects.startIndex }
    var endIndex: Index { weakObjects.endIndex }
    func index(after i: Index) -> Index { weakObjects.index(after: i) }
    subscript(position: Index) -> Element {
        get { weakObjects[position].object }
        set (newValue) { weakObjects[position] = WeakObject(object: newValue) }
    }
    var count: Int { return weakObjects.count }
    var isEmpty: Bool { return weakObjects.isEmpty }
}

extension WeakObjectsArray: RangeReplaceableCollection {
    mutating func replaceSubrange<C : Collection>( _ subrange: Range<Index>, with newElements: C) where Element == C.Element {
        weakObjects.replaceSubrange(subrange, with: newElements.map { WeakObject(object: $0) })
    }
}

选项2使用

class Class2 { // or struct
    var weakObjectsArray = WeakObjectsArray<UIView>() // Use like regular array. With any objects

    func test() {
        weakObjectsArray.append(UIView())
        weakObjectsArray.forEach { print($0) }
    }
}

完整的样品

不要忘记粘贴解决方案代码

import UIKit

class ViewController: UIViewController {

    @WeakElements var weakObjectsArray = [UIView?]()
    //var weakObjectsArray = WeakObjectsArray<UIView>()

    override func viewDidLoad() {
        super.viewDidLoad()
        addSubviews()
    }

    private func printArray(title: String) {
        DispatchQueue.main.async {
            print("=============================\n\(title)\ncount: \(self.weakObjectsArray.count)")
            self.weakObjectsArray.enumerated().forEach { print("\($0) \(String(describing: $1))") }
        }
    }
}

extension ViewController {

    private func createRandomRectangleAndAdd(to parentView: UIView) -> UIView {
        let view = UIView(frame: CGRect(x: Int.random(in: 0...200),
                                        y: Int.random(in: 60...200),
                                        width: Int.random(in: 0...200),
                                        height: Int.random(in: 0...200)))
        let color = UIColor(red: CGFloat.random(in: 0...255)/255,
                            green: CGFloat.random(in: 0...255)/255,
                            blue: CGFloat.random(in: 0...255)/255,
                            alpha: 1)
        view.backgroundColor = color
        parentView.addSubview(view)
        return view
    }

    private func addSubviews() {
        (0...1).forEach { _ in addView() }
        addButtons()
    }

    private func createButton(title: String, frame: CGRect, action: Selector) -> UIButton {
        let button = UIButton(frame: frame)
        button.setTitle(title, for: .normal)
        button.addTarget(self, action: action, for: .touchUpInside)
        button.setTitleColor(.blue, for: .normal)
        return button
    }

    private func addButtons() {
        view.addSubview(createButton(title: "Add",
                                     frame: CGRect(x: 10, y: 20, width: 40, height: 40),
                                     action: #selector(addView)))

        view.addSubview(createButton(title: "Delete",
                                     frame: CGRect(x: 60, y: 20, width: 60, height: 40),
                                     action: #selector(deleteView)))

        view.addSubview(createButton(title: "Remove nils",
                                     frame: CGRect(x: 120, y: 20, width: 100, height: 40),
                                     action: #selector(removeNils)))
    }

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

        printArray(title: "First view deleted")
    }

    @objc func addView() {
        weakObjectsArray.append(createRandomRectangleAndAdd(to: view))
        printArray(title: "View addded")
    }

    @objc func removeNils() {
        weakObjectsArray = weakObjectsArray.filter { $0 != nil }
        printArray(title: "Remove all nil elements in weakArray")
    }
}

由于NSPointerArray已经自动处理了大部分问题，我通过为它做一个类型安全的包装来解决这个问题，这避免了其他答案中的大量样板:

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: index) {
            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
}

使用示例:

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

它在前面做了更多的工作，但在你的代码的其余部分的使用是更干净的我。如果你想让它更像数组，你甚至可以实现下标，使它成为一个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)。

创建一个通用包装器，如下:

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

将该类的实例添加到数组中。

class Stuff {}
var weakly : [Weak<Stuff>] = [Weak(value: Stuff()), Weak(value: Stuff())]

定义Weak时，可以使用struct或class。

同样，为了帮助获取数组内容，你可以做一些如下的事情:

extension Array where Element:Weak<AnyObject> {
  mutating func reap () {
    self = self.filter { nil != $0.value }
  }
}

上面使用的AnyObject应该替换为T -但我不认为当前的Swift语言允许这样定义扩展。

这是一个类型安全的集合，用于保存弱对象的容器。当它被访问时，它也会自动移除nil容器/包装器。

例子:

protocol SomeDelegate: class {
    func doSomething()
}

class SomeViewController: UIViewController {
    var delegates: WeakCollection<SomeDelegate> = []

    func someFunction(delegate: SomeDelegate) {
        delegates.append(delegate)
    }

    func runDelegates() {
        delegates.forEach { $0.doSomething() }
    }
}

自定义集合https://gist.github.com/djk12587/46d85017fb3fad6946046925f36cefdc

import Foundation

/**
 Creates an array of weak reference objects.
 - Important:
    Because this is an array of weak objects, the objects in the array can be removed at any time.
    The collection itself will handle removing nil objects (garbage collection) via the private function cleanUpNilContainers()
 */

class WeakCollection<T>: RangeReplaceableCollection, ExpressibleByArrayLiteral {
    typealias Index = Int
    typealias Element = T
    typealias Iterator = IndexingIterator<[Element]>

    private var weakContainers: [WeakReferenceContainer]

    required convenience init(arrayLiteral: Element...) {
        self.init()
        self.weakContainers = WeakCollection.createWeakContainers(from: arrayLiteral)
    }

    required init() {
        weakContainers = []
    }

    required init<S>(_ elements: S) where S: Sequence, WeakCollection.Element == S.Element {
        self.weakContainers = WeakCollection.createWeakContainers(from: elements)
    }

    static private func createWeakContainers<S>(from weakCollection: S) -> [WeakReferenceContainer] where S: Sequence,
        WeakCollection.Element == S.Element {
            return weakCollection.compactMap { WeakReferenceContainer(value: $0 as AnyObject) }
    }

    func append<S>(contentsOf newElements: S) where S: Sequence, WeakCollection.Element == S.Element {
        self.weakContainers.append(contentsOf: WeakCollection.createWeakContainers(from: newElements))
    }

    var startIndex: Index {
        return references.startIndex
    }

    var endIndex: Index {
        return references.endIndex
    }

    func replaceSubrange<C, R>(_ subrange: R, with newElements: C) where
        C: Collection, R: RangeExpression, WeakCollection.Element == C.Element, WeakCollection.Index == R.Bound {
            weakContainers.replaceSubrange(subrange, with: WeakCollection.createWeakContainers(from: newElements))
    }

    func index(after i: Int) -> Int {
        return references.index(after: i)
    }

    func makeIterator() -> IndexingIterator<[Element]> {
        return references.makeIterator()
    }

    subscript(index: Int) -> Element {
        get {
            return references[index]
        }
        set {
            weakContainers[index] = WeakReferenceContainer(value: newValue as AnyObject)
        }
    }
}

extension WeakCollection {
    private class WeakReferenceContainer {
        private(set) weak var value: AnyObject?

        init(value: AnyObject?) {
            self.value = value
        }
    }

    private func cleanUpNilContainers() {
        weakContainers = weakContainers.compactMap { $0.value == nil ? nil : $0 }
    }

    private var references: [Element] {
        cleanUpNilContainers()
        return weakContainers.compactMap { $0.value as? T }
    }
}

在很多情况下，返回一个可取消的选项会更简洁。这允许调用站点决定何时显式地销毁值(以及通过解压缩隐式地销毁值):

public protocol Cancellable {
    func cancel()
}

private struct MyValue: Identifiable {
    let id: String
    // ...
}

private class CancellationHandler: Cancellable {
    let handler: () -> ()
    init(handler: @escaping () -> ()) { self.handler = handler }
    func cancel() { handler() }
    deinit { handler() }
}

public class Container {
    private var array = [MyType]()

    public func add() -> Cancellable {
        let value = MyValue(...)
        array.append(value)
        return CancellationHandler {
            array.removeFirst(where: { $0.id == value.id })
        }
    }
}

let cancellable = container.add()

// Both cancellable.cancel() and the cancellable descoping 
// will call the `cancel` function, removing the value from array.