ios - Protocol 只能用作泛型约束，因为它有 Self 或关联类型要求

Question

我有这个协议(protocol):

protocol ViewType {
    associatedtype T: ViewData.View
    var data:T! {get set}
}

ViewData.View是一个类

我有一个名为 TemplateLabel 的类，它继承了 UILabel 并符合 ViewType

class TemplateLabel:UILabel, ViewType {
    var data: ViewData.View.Label!
}

我从 Storyboard中获取此 TemplateLabel 作为 UIView 并尝试将 UIView 转换为 ViewType 以分配它的 data 属性

let view = SB.instantiateViewControllerWithIdentifier("view_label").view
if var v = view as? ViewType { // Error
    v.data = data // Error
}

但是我得到错误:

Protocol 'ViewType' can only be used as a generic constraint because it has Self or associated type requirements

Member 'data' cannot be used on value of protocol type 'ViewType'; use a generic constraint instead

Answer 1

我有一个答案给你，但那几乎是裸代码。我认为它真的在定义的上下文中很有用。

import UIKit

// Framework

/**
 * Intended usage:
 *
 *     enum AppStoryboard: BundledStoryboard {
 *
 *         case Login
 *         case Main
 *
 *         var storyboard: UIStoryboard {
 *             return UIStoryboard(name: "\(self)", bundle: nil)
 *         }
 *
 *     }
 */
protocol BundledStoryboard {

    var storyboard: UIStoryboard { get }

}

protocol StoryboardViewController {

    static var bundledStoryboard: BundledStoryboard { get }
    static var storyboardId: String { get }

    static func instantiateFromStoryboard() -> Self

}

extension StoryboardViewController {

    static var storyboardId: String { return "\(self)" }

    static func instantiateFromStoryboard() -> Self {
        return bundledStoryboard.storyboard.instantiateViewControllerWithIdentifier(storyboardId) as! Self
    }

}

// Application specific

enum AppStoryboard: BundledStoryboard {

    //case Login
    case Main

    var storyboard: UIStoryboard {
        return UIStoryboard(name: "\(self)", bundle: nil)
    }

}

extension StoryboardViewController {

    static var bundledStoryboard: BundledStoryboard { return AppStoryboard.Main }

}

// View-Model relation

protocol ViewType {

    associatedtype Model

    func loadModel(m: Model)

}

// ViewController

final class ViewController: UIViewController, StoryboardViewController, ViewType {

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

    func loadModel(m: UIColor?) {
        view.backgroundColor = m // Strange example, yeah.
    }

}

// Then somewhere...

let vc = ViewController.instantiateFromStoryboard()
vc.loadModel(.redColor())

我认为您在这里真的不需要任何动态解决方案。您必须知道您正在实例化什么以及它可以接收哪些数据。