泛型IBDesginables UIView扩展 [英] Generic IBDesginables UIView extension

问题描述

我想为类创建泛型扩展，以便为任何UIView子类添加一些可设计的功能，从而避免为所有子类添加功能。所以，为符合协议的强大的UIView添加扩展会很好，因为它只是一个标记我希望添加功能的类的标记。然后，只需在任何UIView子类中添加该协议，并在其中实现此功能即可：

  protocol SomeProtocol {
 //空
} 
 
类BCBorderedView：UIView，SomeProtocol 
 {
 //空
} 
 
类BCBorderedSearch ：UISearchBar，SomeProtocol 
 {
 //空
} 
  

我的下面的实现接收错误消息

Trailing'where'子句用于扩展非泛型类型'UIView'

  @IBDesignable 
扩展名UIView其中Self：SomeProtocol //错误：尾随'where'子句for扩展非泛型类型'UIView'
 {
 
 @IBInspectable 
 public var cornerRadius：CGFloat 
 {
 set（radius）{
 self.layer.cornerRadius =半径
 self.layer.masksToBounds =半径> 0 
} 
 
获得{
返回self.layer.cornerRadius 
} 
} 
 
 @IBInspectable 
 public var borderWidth：CGFloat 
 {
 set（borderWidth）{
 self.layer.borderWidth = borderWidth 
} 
 
 get {
 return self.layer.borderWidth 
} 
} 
 
 @IBInspectable 
 public var borderColor：UIColor？ 
 {
 set（color）{
 self.layer.borderColor = color？.cgColor 
} 
 
 get {
 if let color = self.layer.borderColor 
 {
 return UIColor（cgColor：color）
} else {
 return nil 
} 
} 
} 
} 
  

删除其中子句编译和工作，但它为所有UIViews及其子类（基本上所有UI元素）添加了功能，这些功能使IB代理不时在故事板中崩溃。

任何想法如何将此计划更新为work？

解决方案

extension Foo其中 ...只能使用如果 Foo 是

• 泛型类或结构
  
• 包含一些关联类型的协议
  
• 一个协议，我们用一个默认实现扩展的时间为
  Self是特定的（对象/参考e）类型，或者符合一些
  类型的约束。
  
  lock
  

  尾随'where'子句对于非泛型类型'UIView'的扩展

  
  

  上面的错误意味着 UIView 是一个非泛型的类类型，所以其中子句不能在这里应用。

  
  
  

  比尝试扩展 UIView ，您必须扩展 SomeProtocol ，其中 Self ：UIView

  
  
  

  您的扩展应该扩展到符合 SomeProtocol 的所有类型的功能，是 UIView

  
  
  

  简而言之，您应该在扩展子句中切换顺序。所以，
  
  

   扩展UIView其中Self：SomeProtocol 
    

  应该是
  
  

   扩展SomeProtocol其中Self：UIView 
    

  
  

  I would like to create generic extension for class to add some designables functionality to any UIView subclass and by this avoid adding functionality to all subclasses. So, would be nice to add extension for UIView which conforms to protocol SomeProtocol (It's empty because it is just a tag to mark classes which I want functionality to be added). Then just add that protocol in any UIView subclass where I want that functionality to be implemented like this:

  protocol SomeProtocol {
    //empty
  }
  
  class BCBorderedView : UIView, SomeProtocol
  {
    //empty
  }
  
  class BCBorderedSearch: UISearchBar, SomeProtocol
  {
    //empty
  }
  

  My implementation below receives error with message

  "Trailing 'where' clause for extension of non-generic type 'UIView'"

  @IBDesignable
  extension UIView where Self:SomeProtocol //Error: Trailing 'where' clause for extension of non-generic type 'UIView'
  {
  
    @IBInspectable
    public var cornerRadius: CGFloat
    {
        set (radius) {
            self.layer.cornerRadius = radius
            self.layer.masksToBounds = radius > 0
        }
  
        get {
            return self.layer.cornerRadius
        }
    }
  
    @IBInspectable
    public var borderWidth: CGFloat
    {
        set (borderWidth) {
            self.layer.borderWidth = borderWidth
        }
  
        get {
            return self.layer.borderWidth
        }
    }
  
    @IBInspectable
    public var borderColor:UIColor?
    {
      set (color) {
          self.layer.borderColor = color?.cgColor
      }
  
      get {
          if let color = self.layer.borderColor
          {
              return UIColor(cgColor: color)
          } else {
              return nil
          }
      }
    }
  }
  

  Removing where clause compiles and works, but it adds functionality to all UIViews and it's subclasses (basically all UI elements) which make IB agent crash from time to time in storyboard.

  Any ideas how this plan can be updated to work?

  解决方案

  extension Foo where ... can only be used if Foo is

  • a generic class or structure
  • a protocol containing some associated types
  • a protocol where we extend with a default implementation for when Self is of a specific (object/reference) type, or conforms to some type constraint.

  Trailing 'where' clause for extension of non-generic type 'UIView'

  The above error implies that UIView is a non-generic class type, and so where clause cannot be applied here.

  So, rather than attempting to extend UIView, you must extend SomeProtocol with a default implementation for cases where Self: UIView

  Your extension should extend functionality to all types that conform to SomeProtocol and are of type UIView

  In a nutshell, you should switch the order in the extension clause. So,

  extension UIView where Self : SomeProtocol
  

  should be

  extension SomeProtocol where Self: UIView
  

  这篇关于泛型IBDesginables UIView扩展的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！