Ios 去公告属性包装器

在花了一些时间创建@Debounced属性包装器之后，我对代码的可读性不满意。要了解发生了什么，您确实需要了解属性包装器是如何工作的，以及wrappedvalue和projectedvalue的概念。这是属性包装器：

    @propertyWrapper
    class Debounced<Input: Hashable> {

    private var delay: Double
    private var _value: Input
    private var function: ((Input) -> Void)?
    private weak var timer: Timer?

    public init(wrappedValue: Input, delay: Double) {
        self.delay = delay
        self._value = wrappedValue
    }

    public var wrappedValue: Input {
        get {
            return _value
        }
        set(newValue) {
            timer?.invalidate()
            timer = Timer.scheduledTimer(withTimeInterval: delay, repeats: false, block: { [weak self] _ in
                self?._value = newValue
                self?.timer?.invalidate()
                self?.function?(newValue)
            })
        }
    }

    public var projectedValue: ((Input) -> Void)? {
        get {
            return function
        }
        set(newValue) {
            function = newValue
        }
    }
}

这是它应该做的。每次设置text属性时，都会调用print函数。如果该值在0.4秒内更新多次，则该函数将只调用一次

但就简单性和可读性而言，我认为创建这样的Debouncer类更好：

---

你觉得怎么样？有没有更好的方法来创建此属性包装器？

它可以正常工作。。。那样的话，就用它吧

嗯。。。但是如何使用它呢？实际上，它不是很灵活，尤其是在编译器声称“不支持多个属性包装器”之前：-）

如果您的目标是在UIKit或SwiftUI应用程序中使用它，我建议您使用不同的方法

让我们尝试一些极简的，但完全工作的SwiftUI示例

//
//  ContentView.swift
//  tmp031
//
//  Created by Ivo Vacek on 26/01/2020.
//  Copyright © 2020 Ivo Vacek. NO rights reserved.
//

import SwiftUI
import Combine

class S: ObservableObject {
    @Published var text: String = ""
    @Published var debouncedText: String = ""

    private var store = Set<AnyCancellable>()
    init(delay: Double) {
        $text
            .debounce(for: .seconds(delay), scheduler: RunLoop.main)
            .sink { [weak self] (s) in
            self?.debouncedText = s
        }.store(in: &store)
    }
}

struct ContentView: View {
    @ObservedObject var model = S(delay: 2)
    var body: some View {
        List {
            Color.clear
            Section(header: Text("Direct")) {
                Text(model.text).font(.title)
            }
            Section(header: Text("Debounced")) {
                Text(model.debouncedText).font(.title)
            }
            Section(header: Text("Source")) {
                TextField("type here", text: $model.text).font(.title)
            }

        }
    }
}


struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

应用程序使用示例

更新：如果您不能使用Combine，但您喜欢类似的语法。。。 首先定义protokol

protocol Debounce: class {
    associatedtype Value: Hashable
    var _value: Value { get set }
    var _completions: [(Value)->Void] { get set}
    var _delay: TimeInterval { get set }
    var _dw: DispatchWorkItem! { get set }
    func debounce(completion: @escaping (Value)->Void)
}

和默认的去盎司函数实现。其思想是，使用与联合收割机上的.publisher.sink（）相同的方法进行去噪_去抖动是去抖动功能的“内部”实现。它比较当前值和“延迟”旧值，如果它们相等，则执行此操作

extension Debounce {
    func debounce(completion: @escaping (Value)->Void) {
        _completions.append(completion)
    }
    func _debounce(newValue: Value, delay: TimeInterval, completions:  [(Value)->Void]) {
        if _dw != nil {
            _dw.cancel()
        }
        var dw: DispatchWorkItem!
        dw = DispatchWorkItem(block: { [weak self, newValue, completions] in
            if let s = self, s._value == newValue {
                for completion in completions {
                    completion(s._value)
                }
            }
            dw = nil
        })
        _dw = dw
        DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: dw)
    }
}

现在我们有了属性包装器的所有组件

@propertyWrapper class Debounced<T: Hashable> {

    final class Debouncer: Debounce {
        typealias Value = T

        var _completions: [(T) -> Void] = []
        var _delay: TimeInterval
        var _value: T {
            willSet {
                _debounce(newValue: newValue, delay: _delay, completions: _completions)
            }
        }
        var _dw: DispatchWorkItem!
        init(_value: T, _delay: TimeInterval) {
            self._value = _value
            self._delay = _delay
        }
    }

    var wrappedValue: T {
        get { projectedValue._value }
        set { projectedValue._value = newValue }
    }

    var projectedValue: Debouncer

    init(wrappedValue: T, delay: TimeInterval) {
        projectedValue = Debouncer(_value: wrappedValue, _delay: delay)
    }
    deinit {
        print("deinit")
    }
}

上面印的是

2020-02-04 09:53:11 +0000 0 initial
0 0.46608517831539165
2020-02-04 09:53:12 +0000 0 debounced A
2020-02-04 09:53:12 +0000 0 debounced B
1 0.97078412234771
2 1.1756938500918692
3 1.236562020385944
4 1.4076127046937024
2020-02-04 09:53:13 +0000 4 debounced A
2020-02-04 09:53:13 +0000 4 debounced B
5 1.9313412744029004
6 2.1617775513150366
2020-02-04 09:53:14 +0000 6 debounced A
2020-02-04 09:53:14 +0000 6 debounced B
7 2.6665465865810205
8 2.9287734023206418
deinit

---

这是一个主观性很强的上下文问题。首先要问一个问题：你到底想做什么？这个方法100%解决这个问题吗？谢谢你的回答！使用swiftUI和Combine的唯一问题是，该解决方案需要支持低于iOS的版本iOS13@MagnusT更新了一些如何更灵活地执行的想法。。。无联合收割机

@propertyWrapper class Debounced<T: Hashable> {

    final class Debouncer: Debounce {
        typealias Value = T

        var _completions: [(T) -> Void] = []
        var _delay: TimeInterval
        var _value: T {
            willSet {
                _debounce(newValue: newValue, delay: _delay, completions: _completions)
            }
        }
        var _dw: DispatchWorkItem!
        init(_value: T, _delay: TimeInterval) {
            self._value = _value
            self._delay = _delay
        }
    }

    var wrappedValue: T {
        get { projectedValue._value }
        set { projectedValue._value = newValue }
    }

    var projectedValue: Debouncer

    init(wrappedValue: T, delay: TimeInterval) {
        projectedValue = Debouncer(_value: wrappedValue, _delay: delay)
    }
    deinit {
        print("deinit")
    }
}

do {
    struct S {
        @Debounced(delay: 0.2) var value: Int = 0
    }

    let s = S()
    print(Date(), s.value, "initial")

    s.$value.debounce { (i) in
        print(Date(), i, "debounced A")
    }

    s.$value.debounce { (i) in
        print(Date(), i, "debounced B")
    }

    var t = 0.0
    (0 ... 8).forEach { (i) in
        let dt = Double.random(in: 0.0 ... 0.6)
        t += dt
        DispatchQueue.main.asyncAfter(deadline: .now() + t) { [t] in
            s.value = i
            print(s.value, t)
        }
    }
}

2020-02-04 09:53:11 +0000 0 initial
0 0.46608517831539165
2020-02-04 09:53:12 +0000 0 debounced A
2020-02-04 09:53:12 +0000 0 debounced B
1 0.97078412234771
2 1.1756938500918692
3 1.236562020385944
4 1.4076127046937024
2020-02-04 09:53:13 +0000 4 debounced A
2020-02-04 09:53:13 +0000 4 debounced B
5 1.9313412744029004
6 2.1617775513150366
2020-02-04 09:53:14 +0000 6 debounced A
2020-02-04 09:53:14 +0000 6 debounced B
7 2.6665465865810205
8 2.9287734023206418
deinit