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
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")
}
}
其他回答
我有同样的想法来创建带有泛型的弱容器。 因此，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可以初始化为任何类型，如果这种类型不符合AnyObject协议，那么应用程序将崩溃，并给出详细的原因。但我现在找不到更好的解决办法。
最初的解决方案是这样定义WeakSet:
class WeakSet<ObjectType: AnyObject>: SequenceType {}
但是在这种情况下，WeakSet不能用协议初始化:
protocol MyDelegate : AnyObject {
func doWork()
}
let weakSet = WeakSet<MyDelegate>()
目前以上代码无法编译(Swift 2.1, Xcode 7.1)。 这就是为什么我放弃符合AnyObject并使用fatalError()断言添加额外的保护。
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。
现在参加派对有点晚了，但试试我的吧。我实现为一个集合而不是数组。
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) })
}
}
使用
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]
注意WeakObjectSet不会接受String类型，而是接受NSString类型。因为，String类型不是AnyType。我的swift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2017年11月添加
我把代码更新为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提到的，我算出NSString不会被释放基于代码在使用。 我抓了抓头，写了MyString类，如下所示。
// 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。那么说它有效就很奇怪了。
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]
然后我发现了一个奇怪的页面可能与这个问题有关。
弱引用保留已释放的NSString(仅限XC9 + iOS Sim)
https://bugs.swift.org/browse/SR-5511
上面说问题已经解决了，但我想知道这是否和这个问题有关。 无论如何，MyString或NSString之间的行为差异超出了这个上下文，但如果有人能解决这个问题，我会很感激。
可以通过创建包装器对象来保存弱指针来实现这一点。
struct WeakThing<T: AnyObject> {
weak var value: T?
init (value: T) {
self.value = value
}
}
然后在数组中使用这些
var weakThings = WeakThing<Foo>[]()
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)。
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