ios - 如何创建面向协议(protocol)的通用服务？

Question

我正在尝试创建一个将为 View Controller 提供数据的协议(protocol)。我正在尝试采用协议(protocol)方法并使事情变得灵活，因此 View Controller 可以使用任何类型的数据。

但是，我收到错误:Protocol 'Serviceable' can only be used as a generic contraint because it has Self or associated type requirements

这就是我想要做的:

protocol Serviceable {
    associatedtype DataType
    func get(handler: ([DataType] -> Void)?)
}

struct PostService: Serviceable {
    func get(handler: ([Postable] -> Void)? = nil) {
        print("Do something...")
    }
}

struct AuthorService: Serviceable {
    func get(handler: ([Authorable] -> Void)? = nil) {
        print("Do something...")
    }
}

protocol Postable {
    var title: String { get set }
    var content: String { get set }
}

protocol ServiceControllable: class {
    var service: Serviceable { get } // Error: Protocol 'Serviceable' can only be used as a generic contraint because it has Self or associated type requirements
}

extension ServiceControllable {
    func setupDataSource() {
        service.get { items in
            // Do something
        }
    }
}

class MyViewController: ServiceControllable {
    let service: Serviceable = PostService() // Error: Same as above

    override func viewDidLoad() {
        super.viewDidLoad()
        setupDataSource()
    }
}

如何设置它以便我的 View Controller 可以实现 ServiceControllable 并可以访问填充表、集合等的通用 setupDataSource？

Answer 1

你想要这样的东西。

import UIKit

protocol Serviceable {
    associatedtype DataType
    func get(handler: ([DataType] -> Void)?)
}

struct PostService: Serviceable {
    func get(handler: ([Postable] -> Void)? = nil) {
        print("Do something...")
    }
}

protocol Authorable {}

struct AuthorService: Serviceable {
    func get(handler: ([Authorable] -> Void)? = nil) {
        print("Do something...")
    }
}

protocol Postable {
    var title: String { get set }
    var content: String { get set }
}

protocol ServiceControllable: class {

    // THIS is the way to use generic-constraint-protocols in protocols.
    associatedtype _Serviceable: Serviceable

    var service: _Serviceable { get }

}

extension ServiceControllable {
    func setupDataSource() {
        service.get { items in
            // Do something
        }
    }
}

class MyViewController: UIViewController, ServiceControllable {

    let service = PostService()

    override func viewDidLoad() {
        super.viewDidLoad()
        setupDataSource()
    }
}

相关文档部分:Protocol Associated Type Declaratio .