如何使用[SomeProtocol]的索引（of :)？

Question

我有一堆是UIViews的類。有些符合特定的協議。我有這些特定的人的數組，但我不能叫:)指數（這個陣列上（該代碼可以被粘貼到一個遊樂場）：

import UIKit 

protocol ViewWithColor {} 

class BlackView: UIView {} 
class WhiteView: UIView {} 
class BlueView: UIView, ViewWithColor {} 
class GreenView: UIView, ViewWithColor {} 
class YellowView: UIView, ViewWithColor {} 

let blackView = BlackView() 
let whiteView = WhiteView() 
let blueView = BlueView() 
let greenView = GreenView() 
let yellowView = YellowView() 

let allViews = [blackView, whiteView, blueView, greenView, yellowView] 
let viewsWithColorArray: [ViewWithColor] = [blueView, greenView, yellowView] 

let index1 = allViews.index(of: blueView) 
let index2 = viewsWithColorArray.index(of: blueView) 

的錯誤是：

cannot invoke 'index' with an argument list of type '(of: BlueView)' 

該函數無法調用，因爲協議ViewWithColor不符合Equatable。我真的需要實現equatable嗎？或者，還有更好的方法？

Answer 1

正如@vadian說，你可以使用index的版本，需要關閉。在這種情況下，您正在查找特定實例，因此請使用index(where: { $0 === blueView })。

的===操作：

Returns a Boolean value indicating whether two references point to the same object instance.

另外，你需要讓你的協議ViewWithColor一個class協議，因爲===只與類實例的作品。

protocol ViewWithColor: class {} 

class BlackView: UIView {} 
class WhiteView: UIView {} 
class BlueView: UIView, ViewWithColor {} 
class GreenView: UIView, ViewWithColor {} 
class YellowView: UIView, ViewWithColor {} 

let blackView = BlackView() 
let whiteView = WhiteView() 
let blueView = BlueView() 
let greenView = GreenView() 
let yellowView = YellowView() 

let allViews = [blackView, whiteView, blueView, greenView, yellowView] 
let viewsWithColorArray: [ViewWithColor] = [blueView, greenView, yellowView] 

let index1 = allViews.index(where: { $0 === blueView }) 
print(index1 ?? -1) 

2 

let index2 = viewsWithColorArray.index(where: { $0 === blueView }) 
print(index2 ?? -1) 

0 

Answer 2

您可以使用封閉語法並檢查類型：

let index1 = allViews.index(where: {$0 is BlueView}) 
let index2 = viewsWithColorArray.index(where: {$0 is BlueView})