AppDelegateHandler

//
//  AppDelegateHandler.swift
//  Pods
//
//  Created by Andrey Zarembo on 10.02.16.
//
//

import Foundation

public class AppDelegateHandler: NSObject, UIApplicationDelegate {
    
}

AppDelegateProxy

//
//  AppDelegateProxy.swift
//  Pods
//
//  Created by Andrey Zarembo on 10.02.16.
//
//

import Foundation
import UIKit

public class AppDelegateProxy: NSObject, UIApplicationDelegate {
    
    public var handlers:[AppDelegateHandler] = []
    
    public override func respondsToSelector(aSelector: Selector) -> Bool {
        
        if self.shouldForwardSelector(aSelector) {
            for handler in self.handlers {
                if handler.respondsToSelector(aSelector) {
                    return true
                }
            }
        }
        return NSObject.instancesRespondToSelector(aSelector)
    }
    
    public override func forwardingTargetForSelector(aSelector: Selector) -> AnyObject? {
        for handler in self.handlers {
            if handler.respondsToSelector(aSelector) {
                return handler
            }
        }
        return nil
    }
    
    private func shouldForwardSelector(aSelector: Selector) -> Bool {
        return isSelector(aSelector, fromProtocol: UIApplicationDelegate.self) &&
            !isSelector(aSelector, fromProtocol: NSObjectProtocol.self)
    }
    
    private func isSelector(aSelector: Selector, fromProtocol aProtocol:Protocol) -> Bool {
        
        let requiredMethod = [false,false,true,true]
        let instanceMethod = [false,true,false,true]

        for callVariant in 0..<4 {
            let methodDescription = protocol_getMethodDescription(aProtocol,
                aSelector,
                requiredMethod[callVariant],
                instanceMethod[callVariant])
            if methodDescription.types != nil && methodDescription.name != nil {
                return true
            }
        }
        
        return false;
    }
}

swift 4.2 version:

//
//  AppDelegateProxy.swift
//  Pods
//
//  Created by Andrey Zarembo on 10.02.16.
//
//

import UIKit

public class AppDelegateProxy: NSObject, UIApplicationDelegate {
	public var handlers: [AppDelegateHandler] = []

	public override func responds(to aSelector: Selector!) -> Bool {
		if shouldForwardSelector(aSelector: aSelector) {
			for handler in handlers {
				if handler.responds(to: aSelector) {
					return true
				}
			}
		}
		return NSObject.instancesRespond(to: aSelector)
	}

	public override func forwardingTarget(for aSelector: Selector!) -> Any? {
		for handler in handlers {
			if handler.responds(to: aSelector) {
				return handler
			}
		}
		return nil
	}

	private func shouldForwardSelector(aSelector: Selector) -> Bool {
		return
			isSelector(aSelector: aSelector, fromProtocol: UIApplicationDelegate.self) &&
			!isSelector(aSelector: aSelector, fromProtocol: NSObjectProtocol.self)
	}

	private func isSelector(aSelector: Selector, fromProtocol aProtocol: Protocol) -> Bool {
		let requiredMethod = [false, false, true, true]
		let instanceMethod = [false, true, false, true]

		for callVariant in 0 ..< 4 {
			let methodDescription = protocol_getMethodDescription(aProtocol,
			                                                      aSelector,
			                                                      requiredMethod[callVariant],
			                                                      instanceMethod[callVariant])
			if methodDescription.types != nil, methodDescription.name != nil {
				return true
			}
		}

		return false
	}
}