有没有办法使用 value(forKeyPath:) 访问 KVC 中的数组元素？答案

【问题标题】：Is there a way to access an array element in KVC using value(forKeyPath:)?有没有办法使用 value(forKeyPath:) 访问 KVC 中的数组元素？
【发布时间】：2018-10-10 21:29:37
【问题描述】：

假设我有一些类似于以下的符合 KVC 的对象：

class Person : NSObject {
   var office: Office
   var firstName: String
   var lastName: String
   var reports: [Report]

   init( office: Office, 
         firstName: String,
         lastName: String,
         reports: [Report] ) {

      ...

   }
}

class Office : NSObject {
   var building: String
   var room: Int

   init( building: String, 
         room: Int ) {

      ...

   }

}

class Report : NSObject {
   var title: String
   var contents: String 

   init( title: String, 
         contents: String ) {

      ...

   }
}

我创建了一个实例，人

let person = Person(
                office: Office( 
                    building: "Main",
                    room: 2 ),
                firstName: "Bob",
                lastName: "Roberts",
                reports: [
                    Report( title: "Today's weather", contents: "..." ),
                    Report( title: "Traffic", contents: "..." ),
                    Report( title: "Stocks", contents: "..." )
                ] )

我可以使用 person.value(forKeyPath:) 来访问 person 的属性和嵌套属性，如下所示：

person.value(forKeyPath: "firstName") // "Bob"
person.value(forKeyPath: "office.room" ) // 2

但是，KVC 中有没有办法从第二个报告中获取标题？

类似

person.value(forKeyPath: "reports[1].title" ) // "Traffic"

【问题讨论】：

标签： swift kvc

【解决方案1】：

Swift 的原生 KVC 甚至可以使用结构体，不需要 ObjC 运行时

struct Person {
    var office: Office
    var firstName: String
    var lastName: String
    var reports: [Report]
}

struct Office {
    var building: String
    var room: Int
}

struct Report {
    var title: String
    var contents: String
}

let person = Person(office: Office(building: "Main", room: 2 ),
                    firstName: "Bob", lastName: "Roberts",
                    reports: [
                        Report( title: "Today's weather", contents: "..." ),
                        Report( title: "Traffic", contents: "..." ),
                        Report( title: "Stocks", contents: "..." )
    ])


let keyPath = \Person.reports[1].title
let title = person[keyPath: keyPath] // "Traffic"

【讨论】：

【解决方案2】：

这里澄清一下：您不需要将 NSObject 类更改为 struct。甚至一堂课也可以工作。我认为这是一个答案。

class Person : NSObject {
    var office: Office!
    @objc var firstName: String!
    var lastName: String!
    @objc var reports: [Report]!

    init( office: Office,
          firstName: String,
          lastName: String,
          reports: [Report] ) {
        super.init()
        self.office = office
        self.firstName = firstName
        self.lastName = lastName
        self.reports = reports
    }
}

class Office : NSObject {
    var building: String!
    var room: Int!

    init( building: String,
          room: Int ) {
        self.building = building
        self.room = room
    }
}

class Report : NSObject {
    var title: String!
    var contents: String!

    init( title: String,
          contents: String ) {
        self.title =  title
        self.contents = contents
    }
}

let person = Person(
    office: Office(
        building: "Main",
        room: 2 ),
    firstName: "Bob",
    lastName: "Roberts",
    reports: [
        Report( title: "Today's weather", contents: "..." ),
        Report( title: "Traffic", contents: "..." ),
        Report( title: "Stocks", contents: "..." )
    ] )


person[keyPath: \Person.reports[1].title]

【讨论】：