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
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。
其他回答
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")
}
}
同样的问题还有另一种解决方案……它的重点是存储对对象的弱引用,但也允许存储结构。
[我不确定它有多有用,但它确实花了一段时间来纠正语法]
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
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>[]()
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。
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.
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