Ios 从对象数组中获取属性值数组

有一个叫做

Employee

的类

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
    }
}

我有一个

Employee

对象数组。我现在需要的是将该数组中所有对象的

id

s提取到一个新数组中

我也发现了类似的情况。但是它在Objective-C中，所以它使用

valueForKeyPath

来实现这一点

---

如何在Swift中实现这一点？

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-在您的例子中，从

员工数组转换为
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 }

Swift 5提供了许多从类似对象数组中获取属性值数组的方法。根据您的需要，您可以从以下六个游戏场代码示例中选择一个来解决您的问题


1.使用
map
方法
使用Swift，符合
序列
协议的类型有一个方法。以下示例代码显示了如何使用它：

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.将
用于
循环

3.使用
while
循环
请注意，对于Swift，幕后的
for
循环只是
，而
在
序列的迭代器上循环（有关更多详细信息，请参阅）


4.使用符合
迭代协议
和
序列
协议的
结构

6.使用KVC和
NSArray
的方法
请注意，此示例要求
类Employee
从
NSObject
继承

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]
}

这就是
map
的作用-它将
Employee
数组转换为
Int
数组，并填充
id
字段。这相当于说“从
Employee
的所有实例中提取id字段并将它们放入数组”@Isuru，这个答案正是您想要的。它创建一个名为
id
的新数组，该数组包含
Employee
s数组中的所有
id
值。注意，它保留了原始数组的完整性。在Swift 2 beta中，正确的语法应该是
array.map（{$0.id}）
如果您使用的是可选的，请确保！信息技术花了我几个小时。@Chris强制展开通常是一种不好的做法，因为如果为零，它将导致应用程序崩溃。只有在严格要求时才使用它，并且更喜欢可选绑定（或任何其他“软”展开）而不是。。。据我所知，这是完整的可能方法列表
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]

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]

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]

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]
}