我想在Swift中存储一个弱引用数组。数组本身不应该是弱引用——它的元素应该是。我认为Cocoa NSPointerArray提供了一个非类型安全的版本。
当前回答
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 }
}
}
其他回答
我基于@Eonil的工作，因为我喜欢闭包弱绑定策略，但我不想为变量使用函数操作符，因为这感觉非常违反直觉
相反，我所做的是:
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
}
}
}
这样你可以做一些事情，比如:
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
你可以和weakObjectsHashTable一起使用NSHashTable。NSHashTable < ObjectType > .weakObjectsHashTable ()
对于Swift 3: NSHashTable<ObjectType>.weakObjects()
NSHashTable类引用
OS X v10.5及以上版本支持。 支持iOS 6.0及以上版本。
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 }
}
}
其他的回答涵盖了泛型的角度。我想分享一些涵盖nil角度的简单代码。
我想要一个静态数组(偶尔读)的所有标签，目前存在于应用程序，但不想看到nil的地方旧的曾经是。
没什么特别的，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))
}
}
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。
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