ios - 结构的深度复制 - 如何？

Question

我有以下结构，我想对其进行深层复制，以便我可以以不同的方式对待它们。

class NearbyStopsViewModel {
    var stopViewModels: [StopViewModel]
}

class StopViewModel {
    var stop: Stop
    var name: String
    var departures: [DepartureViewModel]?
}

class DepartureViewModel: NSObject {
    var departure: Departure
    var name: String
}

我很难全神贯注地制作这个结构的深拷贝，有什么想法吗？

Answer 1

要创建类实例的“深层”副本，您需要遵守这些相关类的 NSCopying，Structs 按值传递。我为缺失的结构添加了自己的实现。

import Foundation

struct Departure {
    var to: Stop
    var from: Stop
    
    init(from: Stop, to: Stop) {
        self.from = from
        self.to = to
    }
}

struct Stop {
    var name: String = ""
    
    init(named: String) {
        self.name = named
    }
}

class NearbyStopsViewModel: NSCopying {
    var stopViewModels: [StopViewModel]
    
    init(stops: [StopViewModel] = []) {
        self.stopViewModels = stops
    }
    
    func copy(with zone: NSZone? = nil) -> Any {
        
        var stops: [StopViewModel] = []
        self.stopViewModels.forEach { (stop) in
            stops.append(stop.copy() as! StopViewModel)
        }
        
        let nearbysvm = NearbyStopsViewModel.init(stops: stops)
        return nearbysvm
        
    }
}

class StopViewModel: NSCopying {
    
    var stop: Stop
    var name: String = ""
    var departures: [DepartureViewModel]
    
    init(stop: Stop, named: String, with departures: [DepartureViewModel] = [] ) {
        self.stop = stop
        self.name = named
        self.departures = departures
    }
    
    func copy(with zone: NSZone? = nil) -> Any {
        
        var departuresCopy: [DepartureViewModel] = []
        self.departures.forEach { (departure) in
            departuresCopy.append(departure.copy() as! DepartureViewModel)
        }
        
        let stopvm = StopViewModel.init(stop: self.stop, named: self.name, with: departuresCopy)
        return stopvm
    }
}


class DepartureViewModel: NSObject, NSCopying {
    
    var departure: Departure
    var name: String = ""
    
    init(name: String, departure: Departure) {
        self.name = name
        self.departure = departure
    }
    
    func copy(with zone: NSZone? = nil) -> Any {
        let departure = DepartureViewModel.init(name: self.name, departure: self.departure)
        return departure
    }
}


// Structs are passed by Value, making a 'minimal' copy of themselves as they move.
var pennStation = Stop(named: "Pennsylvania Station")
print(pennStation)
let copyByValue = pennStation
print(copyByValue) // "Pennsylvania Station"
pennStation.name = "Penn. Station"
print(copyByValue) // "Pennsylvania Station"

// Classes are passed by Reference
let clarkLake = Stop(named: "Clark and Lake")
let stateLake = Stop(named: "State and Lake")

let clarkToState = Departure(from: clarkLake, to: stateLake)

// DepartureViewModel is your lowest level class that conforms to NSCopying
let departure = DepartureViewModel(name: "clark to state", departure: clarkToState)
print(departure) // This Memory Address should never change.
let referenceDeparture = departure
departure.name = "Unexpected delay"
print(referenceDeparture.name)
print(referenceDeparture) // Same Address as departure.

let deepCopyOfDeparture = departure.copy() as! DepartureViewModel // Copy() and mutableCopy() will return a passed-by-value copy.
print(deepCopyOfDeparture) // Different Memory Address as departure


let stopvm = StopViewModel(stop: pennStation, named: "Penn. Station", with: [departure])
print("Stop View Model's Child Departure Instance(s): \(stopvm.departures)")
let copyOfSVM = stopvm.copy() as! StopViewModel
print("Copy of SVM Child Departure Instance(s): \(copyOfSVM.departures)")

输出:

Stop(name: "Pennsylvania Station")

Stop(name: "Pennsylvania Station")

Stop(name: "Pennsylvania Station")

<StackOverflow.DepartureViewModel: 0x149dc4de0>

Unexpected delay

<StackOverflow.DepartureViewModel: 0x149dc4de0>

<StackOverflow.DepartureViewModel: 0x149da89a0>

<Stop View Model's Child Departure Instance(s): <StackOverflow.DepartureViewModel: 0x149dc4de0>

<Copy of SVM Child Departure Instance(s): <StackOverflow.DepartureViewModel: 0x149dc7630>