ios - 从 Swift 中的父类(super class)访问子类属性

Question

我是编程新手，需要一些有关 Swift 继承的帮助。我正在创建一个购物车类型的应用程序，用于在我的业务中创建报价。我有一个产品类，其中包含特定产品类型的子类，因此我可以为它们提供自定义属性。我有一个购物车类，我可以在其中传递产品类别和所需数量。

我的问题是，一旦我创建了产品并将其传递到购物车中，我想访问我的子类中的一个属性，但我不知道如何实现它。请帮助？这是我的代码。

我的产品类别

class ProductItem: NSObject {

var productCode:String!
var productDescription:String!
var manufacturerListPrice:Double!
}

产品子类

class DigitalHandset: ProductItem {

var digitalPortsRequired:Int!

init(productCode: String, listPrice: Double){
    super.init()
    super.productCode = productCode
    super.manufacturerListPrice = listPrice
    super.productDescription = ""

    self.digitalPortsRequired = 1
    }
}

购物车类

public class bomItems: NSObject {

    var quantity:Int
    var productItem:ProductItem

    init(product: ProductItem, quantity: Int) {
        self.productItem = product
        self.quantity = quantity
    }
}

测试类

class testModelCode{
    var system = MasterSystem() // This class holds my array of cart items (BOM or Bill Of Materials) 
    var bomItem1 = bomItems(product: DigitalHandset(productCode: "NEC999", listPrice: 899), quantity: 8)

func addToSystem() {
    system.billOfMaterials.append(bomItem1) //I have a system class that holds an array for the cart items.
    //At this point I want to access a property of the Digital Handset class but it appears that I can not. 
    //Can anyone point me in the right direction to allow this. 
    //The following is what is not working. 
    bomItem2.DigitalHandset.digitalPortsRequired
}

Answer 1

如果 bomItem2 是 ProductItem 类型，您需要将其向下转换为类型 DigitalHandset 才能访问 DigitalHandset 的属性。执行此操作的安全方法是使用条件向下转换 as? 以及可选的绑定(bind) if let 语法:

if let digitalHandset = bomItem2 as? DigitalHandset {
    // if we get here, bomItem2 is indeed a DigitalHandset
    let portsRequired = digitalHandset.portsRequired
} else {
    // bomItem2 is something other than a DigitalHandset
}

如果您要检查很多类，switch 语句会派上用场:

switch bomItem2 {
case digitalHandset as DigitalHandset:
    println("portsRequired is \(digitalHandset.portsRequired)")
case appleWatch as AppleWatch:
    println("type of Apple Watch is \(appleWatch.type)")
default:
    println("hmmm, some other type")
}