有一个名为Employee
的课程。
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
}
}
我有一组Employee
个对象。我现在需要的是将该数组中所有这些对象的id
提取到一个新数组中。
我也发现了类似的question。但是它在Objective-C中,所以它使用valueForKeyPath
来实现这一点。
如何在Swift中执行此操作?
答案 0 :(得分:193)
您可以使用map
方法,将某种类型的数组转换为另一种类型的数组 - 在您的情况下,从Employee
数组转换为Int
数组:
var array = [Employee]()
array.append(Employee(id: 4, firstName: "", lastName: ""))
array.append(Employee(id: 2, firstName: "", lastName: ""))
let ids = array.map { $0.id }
答案 1 :(得分:58)
Swift 3提供了许多方法来从类似对象的数组中获取属性值数组。根据您的需求和品味,您可以选择六个以下的Playground代码示例之一来解决您的问题。
map
方法 Swift为符合Sequence
协议(包括Array
)的类型提供map(_:)
方法。 (另见Transforming an Array)
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]
for
循环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]
while
循环注意,对于Swift,在幕后,for
循环只是while
迭代器上的sequence
循环(有关详细信息,请参阅IteratorProtocol)。
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]
struct
和IteratorProtocol
协议Sequence
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]
Collection
协议扩展和AnyIterator
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]
NSArray
的{{3}}方法请注意,此示例要求class Employee
继承NSObject
。
import Foundation
class Employee: NSObject {
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]
}
有关更多示例,请参阅GitHub的value(forKeyPath:)
。