使用 Runtime 消息转发，实现 AppDelegate 中的代码模块化。

AppDelegate.h

//
//  AppDelegate.h
//  TestMethod
//
//  Created by 柯磊 on 2019/1/2.
//  Copyright © 2019 AMonster. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;


@end

AppDelegate.m

//
//  AppDelegate.m
//  TestMethod
//
//  Created by 柯磊 on 2019/1/2.
//  Copyright © 2019 AMonster. All rights reserved.
//

#import "AppDelegate.h"
@import ObjectiveC;

@interface AppDelegate1 : NSObject <UIApplicationDelegate>
@end
@implementation AppDelegate1
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSLog(@"AppDelegate1 - didFinishLaunchingWithOptions");
    return YES;
}
- (void)applicationWillResignActive:(UIApplication *)application {
    NSLog(@"AppDelegate1 - applicationWillResignActive");
}
@end

@interface AppDelegate2 : NSObject <UIApplicationDelegate>
@end
@implementation AppDelegate2
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSLog(@"AppDelegate2 - didFinishLaunchingWithOptions");
    return YES;
}
- (void)applicationDidBecomeActive:(UIApplication *)application {
    NSLog(@"AppDelegate2 - applicationDidBecomeActive");
}
@end


@interface AppDelegate ()
@property (nonatomic, strong) NSArray<id<UIApplicationDelegate>> *delegates;
@end

@implementation AppDelegate

- (NSArray<id<UIApplicationDelegate>> *)delegates {
    if (!_delegates) {
        _delegates = @[[AppDelegate1 new], [AppDelegate2 new]];
    }
    return _delegates;
}

- (BOOL)respondsToSelector:(SEL)aSelector {
    BOOL ret = [super respondsToSelector:aSelector];
    if (ret) {
        return ret;
    }
    
    for (id<UIApplicationDelegate> delegate in self.delegates) {
        if ([delegate respondsToSelector:aSelector]) {
            return YES;
        }
    }
    return NO;
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    for (NSObject *delegate in self.delegates) {
        if ([delegate respondsToSelector:aSelector]) {
            return [delegate methodSignatureForSelector:aSelector];
        }
    }
    return [super methodSignatureForSelector:aSelector];
}

- (void)forwardInvocation:(NSInvocation *)anInvocation {
    SEL sel = anInvocation.selector;
    
    BOOL isExec = NO;
    for (NSObject *delegate in self.delegates) {
        if ([delegate respondsToSelector:sel]) {
            [anInvocation invokeWithTarget:delegate];
            isExec = YES;
        }
    }
    if (!isExec) {
        [self doesNotRecognizeSelector:sel];
    }
}

@end