ios - 如何使用索引(:) with [SomeProtocol]?

Question

我有一堆 UIView 类。有些符合特定的协议(protocol)。我有一个包含这些特定数组的数组，但我无法在此数组上调用 index(of:)(此代码可以粘贴到 Playground 中):

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)

错误是:

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

无法调用该函数，因为协议(protocol) ViewWithColor 不符合 Equatable。我真的必须实现 equatable 吗？或者有更好的方法吗？

Answer 1

正如@vadian 所说，您可以使用带有闭包的index 版本。在这种情况下，您要查找特定实例，因此请使用 index(where: { $0 === blueView })。

=== 运算符:

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

此外，您需要使协议(protocol) ViewWithColor 成为 class 协议(protocol)，因为 === 仅适用于类实例。

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