Obtenir un tableau de valeurs de propriété à partir d'un tableau d'objets

Il y a une classe appelée Employee.

class Employee {

    var id: Int
    var firstName: String
    var lastName: String
    var dateOfBirth: NSDate?

    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }
}

Et j'ai une panoplie d' Employeeobjets. Ce dont j'ai maintenant besoin, c'est d'extraire le ids de tous ces objets de ce tableau dans un nouveau tableau.

J'ai également trouvé cette question similaire . Mais c'est en Objective-C donc il est utilisé valueForKeyPathpour accomplir cela.

Comment puis-je faire cela dans Swift?

Vous pouvez utiliser la mapméthode, qui transforme un tableau d'un certain type en un tableau d'un autre type - dans votre cas, du tableau de Employeeau tableau de Int:

var array = [Employee]()
array.append(Employee(id: 4, firstName: "", lastName: ""))
array.append(Employee(id: 2, firstName: "", lastName: ""))

let ids = array.map { $0.id }

Swift 5 offre de nombreuses façons d'obtenir un tableau de valeurs de propriété à partir d'un tableau d'objets similaires. Selon vos besoins, vous pouvez choisir l'un des six exemples de code Playground suivants pour résoudre votre problème.

1. Utilisation de la mapméthode

Avec Swift, les types conformes au Sequenceprotocole ont une map(_:)méthode. L'exemple de code suivant montre comment l'utiliser:

class Employee {
    
    let id: Int, firstName: String, lastName: String
    
    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }

}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]

let idArray = employeeArray.map({ (employee: Employee) -> Int in
    employee.id
})
// let idArray = employeeArray.map { $0.id } // also works
print(idArray) // prints [1, 2, 4]

2. Utilisation de la forboucle

class Employee {
    
    let id: Int, firstName: String, lastName: String

    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }

}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]

var idArray = [Int]()    
for employee in employeeArray {
    idArray.append(employee.id)
}
print(idArray) // prints [1, 2, 4]

3. Utilisation de la whileboucle

Notez qu'avec Swift, dans les coulisses, une forboucle n'est qu'une whileboucle sur sequencel'itérateur d'un (voir IteratorProtocol pour plus de détails).

class Employee {
    
    let id: Int, firstName: String, lastName: String
    
    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }

}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]

var idArray = [Int]()
var iterator = employeeArray.makeIterator()    
while let employee = iterator.next() {
    idArray.append(employee.id)
}
print(idArray) // prints [1, 2, 4]

4. Utilisation d'un structconforme aux protocoles IteratorProtocoletSequence

class Employee {
    
    let id: Int, firstName: String, lastName: String
    
    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }
    
}

struct EmployeeSequence: Sequence, IteratorProtocol {
    
    let employeeArray: [Employee]
    private var index = 0
    
    init(employeeArray: [Employee]) {
        self.employeeArray = employeeArray
    }
    
    mutating func next() -> Int? {
        guard index < employeeArray.count else { return nil }
        defer { index += 1 }
        return employeeArray[index].id
    }
    
}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]
let employeeSequence = EmployeeSequence(employeeArray: employeeArray)
let idArray = Array(employeeSequence)
print(idArray) // prints [1, 2, 4]

5. Utilisation de l' Collectionextension de protocole etAnyIterator

class Employee {
    
    let id: Int, firstName: String, lastName: String
    
    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }

}

extension Collection where Iterator.Element: Employee {
    
    func getIDs() -> Array<Int> {
        var index = startIndex
        let iterator: AnyIterator<Int> = AnyIterator {
            defer { index = self.index(index, offsetBy: 1) }
            return index != self.endIndex ? self[index].id : nil
        }
        return Array(iterator)
    }
    
}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]

let idArray = employeeArray.getIDs()
print(idArray) // prints [1, 2, 4]

6. Utilisation de NSArrayla value(forKeyPath:)méthode KVC et

Notez que cet exemple nécessite class Employeed'hériter de NSObject.

import Foundation

class Employee: NSObject {

    @objc let id: Int, firstName: String, lastName: String

    init(id: Int, firstName: String, lastName: String) {
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
    }

}

let employeeArray = [
    Employee(id: 1, firstName: "Jon", lastName: "Skeet"),
    Employee(id: 2, firstName: "Darin", lastName: "Dimitrov"),
    Employee(id: 4, firstName: "Hans", lastName: "Passant")
]

let employeeNSArray = employeeArray as NSArray
if let idArray = employeeNSArray.value(forKeyPath: #keyPath(Employee.id)) as? [Int] {
    print(idArray) // prints [1, 2, 4]
}