花了一些时间创建@Debounced属性包装器后，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的工作方式以及包装值和投影值的概念。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
}
}
}
属性包装器的用法如下:
@Debounced(delay: 0.4) var text: String? = nil
override func viewDidLoad() {
super.viewDidLoad()
self.$text = { text in
print(text)
}
}
它可以正常工作。每次设置text属性时，都会调用打印功能。如果在0.4秒内多次更新该值，则该函数将仅被调用一次。
但就简单性和可读性而言，我认为最好创建一个像这样的Debouncer类:https://github.com/webadnan/swift-debouncer。
你怎么看？有没有更好的方法来创建此属性包装器？
最佳答案
它可以正常工作……在这种情况下，只需使用它即可!
嗯...但是如何使用呢？实际上，它不是非常灵活，尤其是在编译器声明“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，建议您使用其他方法。
让我们尝试一些简约但可以正常工作的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: $model.text).font(.title)
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
您仍然可以根据需要多次订阅Publisher的
model.$debouncedText。而且，如果您希望使用自己的动作来执行操作，也没问题!model.$debouncedText
.sink { (s) in
doSomethingWithDebouncedValue(s)
}
示例应用程序用法
更新:，如果您不能使用Combine，但是您喜欢类似的语法...
首先定义protokol
protocol Debounce: class {
associatedtype Value: Hashable
var _value: Value { get set }
var _completions: [(Value)->Void] { get set}
var _delay: TimeInterval { get set }
var _dw: DispatchWorkItem! { get set }
func debounce(completion: @escaping (Value)->Void)
}
和默认实现的反跳功能。这个想法是，与在Combine上使用.publisher.sink()相同的方式来使用防抖动。 _debounce是反跳功能的“内部”实现。它比较当前值和“延迟”旧值，如果它们相等，则执行此操作。
extension Debounce {
func debounce(completion: @escaping (Value)->Void) {
_completions.append(completion)
}
func _debounce(newValue: Value, delay: TimeInterval, completions: [(Value)->Void]) {
if _dw != nil {
_dw.cancel()
}
var dw: DispatchWorkItem!
dw = DispatchWorkItem(block: { [weak self, newValue, completions] in
if let s = self, s._value == newValue {
for completion in completions {
completion(s._value)
}
}
dw = nil
})
_dw = dw
DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: dw)
}
}
现在，我们有了属性包装器的所有组件。
@propertyWrapper class Debounced<T: Hashable> {
final class Debouncer: Debounce {
typealias Value = T
var _completions: [(T) -> Void] = []
var _delay: TimeInterval
var _value: T {
willSet {
_debounce(newValue: newValue, delay: _delay, completions: _completions)
}
}
var _dw: DispatchWorkItem!
init(_value: T, _delay: TimeInterval) {
self._value = _value
self._delay = _delay
}
}
var wrappedValue: T {
get { projectedValue._value }
set { projectedValue._value = newValue }
}
var projectedValue: Debouncer
init(wrappedValue: T, delay: TimeInterval) {
projectedValue = Debouncer(_value: wrappedValue, _delay: delay)
}
deinit {
print("deinit")
}
}
让我们尝试一下
do {
struct S {
@Debounced(delay: 0.2) var value: Int = 0
}
let s = S()
print(Date(), s.value, "initial")
s.$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)
}
}
}
打印类似
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
关于ios - 防弹 wrapper ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/59896772/