将数组指针传递给另一个类，并为将来的Swift保留一个引用

Question

我已经成功地通过引用传递了数组。但是，我想保留引用，以便我可以在另一个类中管理数组。

子类化解析和使用NSManaged如下:

class User: PFUser {
    // MARK: Managed Properties
    @NSManaged private var pets: [Pet]
    // MARK: Properties
    private(set) lazy var petList: PetList = PetList(user: self, pets: &self.pets)
    // non-essentials are omitted
}

和PetList类:

class PetList {
    private         var owner: User
    private(set)    var pets: [Pet]
    init(user: User, inout pets: [Pet]) {
        self.owner = user
        self.pets = pets
    }
    func appendPet(pet: Pet) {
        pet.owner = self.owner
        self.pets.append(pet)
    }
}

在init函数中，我试图获得对数组的引用。从那里，我想修改数组在PetList类(如在appendPet .

如何在PetList类中设置变量，使其指向User类中的数组

Answer 1

最简单的方法是创建一个计算属性(如果它应该对所有者的宠物进行操作):

class PetList {
    private         var owner: User
    private(set)    var pets: [Pet] {
        get{ return owner.pets }
        set{ owner.pets = newValue }
    }
    init(user: User) {
        self.owner = user
    }
    func appendPet(pet: Pet) {
        pet.owner = self.owner
        self.pets.append(pet)
    }
}

但是对于许多宠物来说，这可能很慢，因为每次更改数组时都要设置主人的宠物。

另一种方法是将数组包装在类中:

class ArrayWrapper<T> {
    var array: [T]
    init(_ array: [T]) {
        self.array = array
    }
}

然后只使用包装器而不是数组:

class User: PFUser {
    // MARK: Managed Properties
    @NSManaged private var pets: ArrayWrapper<Pet>
    // MARK: Properties
    private(set) lazy var petList: PetList = PetList(user: self, pets: self.pets)
    // non-essentials are omitted
}
class PetList {
    private         var owner: User
    private(set)    var pets: ArrayWrapper<Pet>
    init(user: User, pets: ArrayWrapper<Pet>) {
        self.owner = user
        self.pets = pets
    }
    func appendPet(pet: Pet) {
        pet.owner = self.owner
        // operate only though the wrapper with .array
        self.pets.array.append(pet)
    }
}

旁注:为了避免引用循环，您可能应该使变量owner weak或unowned。

Answer 2

在swift中解决问题的合适方法是使用类的扩展来将所有Pet相关的函数添加到User类中