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
现有的WeakContainer示例很有帮助，但它并不能真正帮助在现有的快速容器(如列表和字典)中使用弱引用。
如果您想使用List方法，如contains，那么WeakContainer将需要实现Equatable。因此，我添加了允许WeakContainer是相等的代码。
如果您想在字典中使用WeakContainer，我还将其设置为可哈希的，以便可以将其用作字典键。
我还将其重命名为WeakObject，以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事情，比如使用弱引用字典:
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)
}
其他回答
函数式样式包装器呢?
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在。
let isAlive = captured1() != nil
let theValue = captured1()!
你可以把闭包存储到一个数组中。
let array1 = Array<() -> (Class1?)>([captured1, captured2, captured3])
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() }))
实际上，你不需要一个函数来创建闭包。直接捕获一个对象。
let captured3 = { [weak obj3] in return obj3 }
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 }
}
}
下面是如何使@GoZoner的伟大的答案符合哈希，所以它可以在容器对象中索引:集，字典，数组等。
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
}
现有的WeakContainer示例很有帮助，但它并不能真正帮助在现有的快速容器(如列表和字典)中使用弱引用。
如果您想使用List方法，如contains，那么WeakContainer将需要实现Equatable。因此，我添加了允许WeakContainer是相等的代码。
如果您想在字典中使用WeakContainer，我还将其设置为可哈希的，以便可以将其用作字典键。
我还将其重命名为WeakObject，以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事情，比如使用弱引用字典:
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)
}
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
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