.h文件

//
//  RuntimeTest.h
//  charReverse
//
//  Created by huant on 2019/3/22.
//  Copyright © 2019 huant. All rights reserved.
//

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface RuntimeTest : NSObject

- (void)test:(NSString*)str;

@end

NS_ASSUME_NONNULL_END

.m文件（resolveInstanceMethod方法里，动态添加方法实现）

//
//  RuntimeTest.m
//  charReverse
//
//  Created by huant on 2019/3/22.
//  Copyright © 2019 huant. All rights reserved.
//

#import "RuntimeTest.h"
#import <objc/runtime.h>

@implementation RuntimeTest


void eat(id selfName, SEL _cmdName, NSString *param){
    NSLog(@"调用eat 参数：1%@ 参数2：%@ 参数3：%@",selfName,NSStringFromSelector(_cmdName),param);
    NSLog(@"%s", __func__);

}

+ (BOOL)resolveInstanceMethod:(SEL)sel{
    
    if (sel == @selector(test:)) {
        NSLog(@"%s", __func__);
        
        BOOL isSuccess = class_addMethod(self, sel, (IMP)eat, "v@::");

        NSLog(@" 是否添加成功：%d", isSuccess);
        return isSuccess;
    }else{
        return [super resolveInstanceMethod:sel];
    }
}


- (id)forwardingTargetForSelector:(SEL)aSelector{
    NSLog(@"%s", __func__);

    return nil;
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector{
    
    if (aSelector == @selector(test:)) {
        NSLog(@"%s", __func__);

        return [NSMethodSignature signatureWithObjCTypes:"v@::"];
    }else{
        return [super methodSignatureForSelector:aSelector];
    }
}

- (void)forwardInvocation:(NSInvocation *)anInvocation{
    NSLog(@"%s", __func__);

}
@end

调用

- (void)viewDidLoad {
    [super viewDidLoad];
    
    RuntimeTest * test = [RuntimeTest new];
    [test test:@"小猫"];
}