Swift 5 offre molti modi per ottenere un array di valori di proprietà da un array di oggetti simili. In base alle tue esigenze, puoi scegliere uno dei sei seguenti esempi di codice di Playground per risolvere il tuo problema.
1. Usando il map
metodo
Con Swift, i tipi conformi al Sequence
protocollo hanno un map(_:)
metodo. Il codice di esempio seguente mostra come utilizzarlo:
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. Utilizzo di for
loop
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. Utilizzo di while
loop
Nota che con Swift, dietro le quinte, un for
loop è solo un while
loop su un sequence
iteratore di (vedi IteratorProtocol per maggiori dettagli).
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. Utilizzo di un struct
che è conforme a IteratorProtocol
e Sequence
protocolli
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. Utilizzo Collection
dell'estensione del protocollo eAnyIterator
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. Utilizzo NSArray
del value(forKeyPath:)
metodo di KVC e
Nota che questo esempio richiede class Employee
di ereditare da 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]
}
map
fa: trasforma un array diEmployee
in un array diInt
, riempito con ilid
campo. Che equivale a dire "estrai il campo id da tutte le istanze diEmployee
e inseriscili in un array"