Swinner中的枚举是枚举吗？ [英] Arrays of enums are enums in Swift?

问题描述

我正在关注 Apple's Swift / iOS教程，它具有以下代码行：

  button.setImage （filledStarImage，forState：[UIControlState.Highlighted，UIControlState.Selected]）
  

c $ c> UIButton.setImage 的签名是：

  public func setImage（image：UIImage ？，forState state：UIControlState）
  

没有重载 setImage 接受 [UIControlState]（）数组。

显然有些voodoo正在进行，可以任何人解释？

解决方案

在Swift中， UIControlState 本身不是枚举，但实际上是一个结构。从 UIControl 的语言参考：

控制状态

控制的状态;一个控件在
时间可以有多个状态。各国根据控制情况有所不同。对于
示例，可以配置一个UIButton实例（使用
setImage：forState：方法），以便在处于
正常状态时显示一个图像，

 <$> c $ c> struct UIControlState：OptionSetType {
 init（rawValue rawValue：UInt）
 static var正常：UIControlState {get} 
 static var Highlighted：UIControlState {get} 
 static var禁用：UIControlState {get} 
 static var选择：UIControlState {get} 
 static var Focused：UIControlState {get} 
 static var应用程序：UIControlState {get} 
 static var保留： UIControlState {get} 
} 
  

OptionSetType 协议（ UIControlState 符合），这允许我们对结构属性，因为它们具有 RawValue ，即 BitwiseOperationsType 。例如：

  struct MyStruct：OptionSetType {
 private var value：UInt 
 var rawValue：UInt {return self.value} 
 init（rawValue value：UInt）{self.value = value} 
 
 static var正常：MyStruct {return self.init（rawValue：1& } 
 static var Highlighted：MyStruct {return self.init（rawValue：1 << 1）} 
 static var Disable：MyStruct {return self.init（rawValue：1& } 
 // ... 
} 
 
 let MyOptionsA：MyStruct = [MyStruct.Normal，MyStruct.Disable] 
 let MyOptionsB：MyStruct = [.Normal， .Disable] 
 
 MyOptionsB.contains（.Highlighted）// false 
 MyOptionsB.contains（.Normal）// true 
  

查看符合 OptionsSetType 的实例方法（请参阅下面的链接到语言ref）。此外，成员管理（例如 .contains（...）如上所述;还有 .remove（...）， .insert（..）），整齐的操作如 union（...） c $ c> intersect（...）也可用。

所以总结一下;你是对的， UIButton.setImage 签名要求 forState状态：UIControlState ，但是，由于 OptionSetType 协议，数组查找 [UIControlState.Highlighted，UIControlState.Selected] 实际上是调用结构类型的有效参数参数 UIControlState 。

请注意，根据上面的示例，结构名称可以省略，因此发送 [。Highlighted，.Selected] code> as forState 参数会一样好。

---

参考&好的阅读：

• OptionSetType协议语言参考


• 如何在Swift 2中枚举OptionSetType？


• http://www.informit.com/articles/article.aspx?p=2420231

ul>


I'm following Apple's Swift/iOS tutorial and it features this line of code:

button.setImage( filledStarImage, forState: [UIControlState.Highlighted, UIControlState.Selected] )

But the definition of UIButton.setImage's signature is:

public func setImage(image: UIImage?, forState state: UIControlState)

There is no overload of setImage that accepts an [UIControlState]() array.

Obviously some voodoo is going on, can anyone explain?

解决方案

In Swift, the UIControlState is not, per se, an enum, but actually a structure. From the language reference for UIControl:

Control State

The state of a control; a control can have more than one state at a time. States are recognized differently depending on the control. For example, a UIButton instance may be configured (using the setImage:forState: method) to display one image when it is in its normal state and a different image when it is highlighted.

Declaration

struct UIControlState : OptionSetType {
    init(rawValue rawValue: UInt)
    static var Normal: UIControlState { get }
    static var Highlighted: UIControlState { get }
    static var Disabled: UIControlState { get }
    static var Selected: UIControlState { get }
    static var Focused: UIControlState { get }
    static var Application: UIControlState { get }
    static var Reserved: UIControlState { get }
}

The key here is the OptionSetType protocol (to which UIControlState conforms), which allows us to do "enum-like" access to the static structures properties, given that these have a RawValue that is a BitwiseOperationsType. E.g.:

struct MyStruct : OptionSetType {
    private var value: UInt
    var rawValue: UInt { return self.value }
    init(rawValue value: UInt) { self.value = value }

    static var Normal: MyStruct { return self.init(rawValue: 1 << 0) }
    static var Highlighted: MyStruct { return self.init(rawValue: 1 << 1) }
    static var Disable: MyStruct { return self.init(rawValue: 1 << 2) }
        // ...
}

let MyOptionsA : MyStruct = [MyStruct.Normal, MyStruct.Disable]
let MyOptionsB : MyStruct = [.Normal, .Disable]

MyOptionsB.contains(.Highlighted) // false
MyOptionsB.contains(.Normal) // true

Have a look at the instance methods (see link to language ref below) made available by conforming to the OptionsSetType. In addition membership management (e.g. .contains(...) as above; also, .remove(...), .insert(..)), neat set operations such as union(...) and intersect(...) are also available.

So to summarize; you are right that the UIButton.setImage signature asks for forState state: UIControlState, but, due to the OptionSetType protocol, the array-looking [UIControlState.Highlighted, UIControlState.Selected] is in fact a valid argument for call to structure type parameter UIControlState.

Note also, as per my example above, that the structure name can be left out, so sending [.Highlighted, .Selected] as forState argument would be just as fine.

---

Reference & good reads:

• OptionSetType Protocol Language Reference
• How do you enumerate OptionSetType in Swift 2?
• http://www.informit.com/articles/article.aspx?p=2420231

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