检查Swift类是否符合协议并实现可选功能？

Question

我正在Swift中编写一个辅助函数,用于SpriteKit游戏,它将检查是否已正确设置了冲突拘留.

我想检查我的GameScene是否实现了协议SKPhysicsContactDeletegate并且还包含该didBeginContact功能.

我有以下代码,在Xcode的自动完成的帮助下编写:

    if GameScene(conformsToProtocol(SKPhysicsContactDelegate)) {
        if GameScene(respondsToSelector(didBeginContact(SKPhysicsContact))) {
            print("Self implements SKPhysicsContactDelegate and didBeginContact appears to be present")
        }
    }

然后Xcode抱怨我的conformsToProtocol抱怨

'参数标签'(_ :)'与任何可用的重载都不匹配'

没有任何建议如何解决.它也反对respondsToSelector,说明这一点

'无法将类型的值'(SKPhysicsContact).Type'(又名'SKPhysicsContact.Type')转换为预期的参数类型'SKPhysicsContact'

如何检查我的GameScene是否符合此协议并实现此功能？

编辑:这是我的代码基于答案:

if GameScene.self is SKPhysicsContactDelegate {
    print("Yes it's a delegate")
}

输出: Yes it's a delegate

let yy = (GameScene.self as? SKPhysicsContactDelegate)?.didBeginContact
print("yy is \(yy)")

输出: yy is nil

if (GameScene.self as? SKPhysicsContactDelegate)?.didBeginContact != nil {
    print("Yes it's a delegate and the function is there")
}

没有输出.

Answer 1

你还在思考Objective-C,拥抱Swift!

假设您的协议如下所示:

@objc protocol SKPhysicsContactDelegate {
    optional func didBeginContact()
}

试试这个:

if let delegate = gameScene as? SKPhysicsContactDelegate {
    delegate.didBeginContact?()
}

或者一个班轮:

(gameScene as? SKPhysicsContactDelegate)?.didBeginContact?()

请注意?调用中的方法名称之后？这是因为该方法是可选的,如果对象没有实现该方法,则不会调用它.而if let如果对象不符合分支不再执行SKPhysicsContactDeletegate协议.

没有通话检查方法存在

要在调用之前检查方法本身是否存在,只需省略方法调用以获取对该方法的引用,并像任何其他变量一样检查它:

if let method = (gameScene as? SKPhysicsContactDelegate)?.didBeginContact {
    print("gameScene conforms to SKPhysicsContactDelegate and implements didBeginContact")
    // Call it later whenever you want
    method()
}

如果您以后不需要再打电话,请检查nil:

if (gameScene as? SKPhysicsContactDelegate)?.didBeginContact != nil {
    print("gameScene conforms to SKPhysicsContactDelegate and implements didBeginContact")
}

检查静态方法

检查optional static方法使用相同的方法,但需要类对象而不是类的实例:

if (GameScene.self as? OptionalProtocol.Type)?.staticMethod != nil {
    print("gameScene conforms to OptionalProtocol and implements staticMethod")
}

请注意GameScene.self获取对象类型并<protocol>.Type转换为协议类而不是协议实例.

完整样本

随附Playgrounds,Swift脚本或任何在线Swift编译器的完整示例:

import Foundation

@objc protocol OptionalProtocol {
    optional func instanceMethod()
    optional static func staticMethod()
}

class Nothing {}
class Something: OptionalProtocol {}
class Bar: NSObject, OptionalProtocol {
    func instanceMethod() {
        print("Instance method")
    }
}
class Foo: NSObject, OptionalProtocol {
    static func staticMethod() {
        print("Static method")
    }
}

// Cast instances to 'Any' and classes to 'AnyClass'
let nothing: Any = Nothing()
let nothingClass: AnyClass = Nothing.self
let something: Any = Something()
let somethingClass: AnyClass = Something.self
let bar: Any = Bar()
let barClass: AnyClass = Bar.self
let foo: Any = Foo()
let fooClass: AnyClass = Foo.self

nothing is OptionalProtocol // false
(nothing as? OptionalProtocol)?.instanceMethod != nil // false
(nothing as? OptionalProtocol)?.instanceMethod?() // Does nothing
(nothingClass as? OptionalProtocol.Type)?.staticMethod != nil // false
(nothingClass as? OptionalProtocol.Type)?.staticMethod?() != nil // Does nothing

something is OptionalProtocol // true
(something as? OptionalProtocol)?.instanceMethod != nil // false
(something as? OptionalProtocol)?.instanceMethod?() // Does nothing
(somethingClass as? OptionalProtocol.Type)?.staticMethod != nil // false
(somethingClass as? OptionalProtocol.Type)?.staticMethod?() != nil // Does nothing

bar is OptionalProtocol // true
(bar as? OptionalProtocol)?.instanceMethod != nil // true
(bar as? OptionalProtocol)?.instanceMethod?() // Prints 'Instance method'
(barClass as? OptionalProtocol.Type)?.staticMethod != nil // false
(barClass as? OptionalProtocol.Type)?.staticMethod?() != nil // Does nothing

foo is OptionalProtocol // true
(foo as? OptionalProtocol)?.instanceMethod != nil // false
(foo as? OptionalProtocol)?.instanceMethod?() // Does nothing
(fooClass as? OptionalProtocol.Type)?.staticMethod != nil // true
(fooClass as? OptionalProtocol.Type)?.staticMethod?() != nil // Prints 'Static method'