符合协议和类的Swift属性 [英] Swift Property that conforms to a Protocol and Class

问题描述

  @property（strong，nonatomic）UIViewController< UITableViewDelegate> *事情; 
  

我想在Swift中实现一个像Objective-C代码中的属性。所以这里是我试过的：

  class AClass< T：UIViewController where T：UITableViewDelegate> ;: UIViewController {
 var thing：T！ 
} 
  

编译。我从故事板中添加属性时出现问题。 @IBOutlet 标记会产生编译器错误。

  class AClass< T ：UIViewController where T：UITableViewDelegate>：UIViewController {
 @IBOutlet weak var anotherThing：UILabel！ //错误
 var thing：T！ 
 
 $ / code> 

错误：

< pre $











$ b $我是否正在执行这项权利？我可以做些什么来解决或解决这个错误？

编辑：

Swift 4终于有了解决这个问题的办法。

解决方案

Swift 4的更新

Swift 4增加了对将类型表示为符合协议的类的支持。语法是 Class&协议。下面是一些使用Swift新特性的概念示例代码（WWDC 2017会话402）：

$ p $协议Shakeable {
func shake（）
}
扩展UIButton：Shakeable {/ * ... * /}
扩展UISlider：Shakeable {/ * ... * /}

//通用示例函数来一般地控制某些控件元素
func shakeEm（控件：[UIControl& Shakeable]）{
用于控件的控件，其中control.isEnabled {
控件.shake（）
}
}


从Swift 3开始，这种方法会导致问题，因为您无法传入正确的类型。如果你尝试传入 [UIControl] ，它没有 shake 方法。如果您尝试传入 [UIButton] ，那么代码将会编译，但不能传入任何 UISlider 秒。如果你传入 [Shakeable] ，那么你不能检查 control.state ，因为 Shakeable 没有那个。 Swift 4终于解决了这个问题。

旧答案

这个问题暂时用下面的代码：

  //这个类用来替换UIViewController< UITableViewDelegate> 
 // Objective-C 
中的声明ConformingClass：UIViewController，UITableViewDelegate {} 
 $ b class AClass：UIViewController {
 @IBOutlet weak var anotherThing：UILabel！ 
 var thing：ConformingClass！ 
} 
  

这对我来说似乎很ha ha。如果需要任何委托方法，那么我将不得不在 ConformingClass （我不想这样做）中实现这些方法，并在子类中重写它们。 p>

我发布了这个答案，以防其他人遇到此问题并且我的解决方案可以帮助他们，但我对解决方案不满意。如果有人发布了更好的解决方案，我会接受他们的回答。

@property (strong, nonatomic) UIViewController<UITableViewDelegate> *thing;

I want to implement a property like in this Objective-C code in Swift. So here is what I've tried:

class AClass<T: UIViewController where T: UITableViewDelegate>: UIViewController {
    var thing: T!
}

This compiles. My problem comes when I add properties from the storyboard. The @IBOutlet tag generates an compiler error.

class AClass<T: UIViewController where T: UITableViewDelegate>: UIViewController {
    @IBOutlet weak var anotherThing: UILabel!  // error
    var thing: T!
}

The error:

Variable in a generic class cannot be represented in Objective-C

Am I implementing this right? What can I do to fix or get around this error?

EDIT:

Swift 4 finally has a solution for this problem. See my updated answer.

解决方案

Update for Swift 4

Swift 4 has added support for representing a type as a class that conforms to a protocol. The syntax is Class & Protocol. Here is some example code using this concept from "What's New in Swift" (session 402 from WWDC 2017):

protocol Shakeable {
    func shake()
}
extension UIButton: Shakeable { /* ... */ }
extension UISlider: Shakeable { /* ... */ }

// Example function to generically shake some control elements
func shakeEm(controls: [UIControl & Shakeable]) {
    for control in controls where control.isEnabled {
        control.shake()
    }
}

As of Swift 3, this method causes problems because you can't pass in the correct types. If you try to pass in [UIControl], it doesn't have the shake method. If you try to pass in [UIButton], then the code compiles, but you can't pass in any UISliders. If you pass in [Shakeable], then you can't check control.state, because Shakeable doesn't have that. Swift 4 finally addressed the topic.

Old Answer

I am getting around this problem for the time being with the following code:

// This class is used to replace the UIViewController<UITableViewDelegate> 
// declaration in Objective-C
class ConformingClass: UIViewController, UITableViewDelegate {}

class AClass: UIViewController {
    @IBOutlet weak var anotherThing: UILabel!
    var thing: ConformingClass!
}

This seems hackish to me. If any of the delegate methods were required, then I would have to implement those methods in ConformingClass (which I do NOT want to do) and override them in a subclass.

I have posted this answer in case anyone else comes across this problem and my solution helps them, but I am not happy with the solution. If anyone posts a better solution, I will accept their answer.

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