OC中是不支持多繼承的，但是某些情況下想實(shí)現(xiàn)類似多繼承的效果怎么辦呢？簡(jiǎn)單的總結(jié)了幾種實(shí)現(xiàn)偽多繼承的方法。不對(duì)之處歡迎大家指正！

第一種：組合

比如魚類會(huì)游泳，鳥類會(huì)飛，現(xiàn)在有個(gè)怪物類，要求既會(huì)飛又會(huì)游泳該怎么辦？就是在怪物類里各持有一個(gè)魚類和鳥類的實(shí)例，外界調(diào)用怪物的飛行方法實(shí)際是其持有的鳥類實(shí)例調(diào)用鳥類飛行的方法，游泳方法亦是如此。直接上代碼吧！

//Fish.h的代碼
#import <Foundation/Foundation.h>

@interface Fish : NSObject
//游泳
- (void)swim;
@end

#import "Fish.h"
//Fish.m的代碼
@implementation Fish

- (void)swim {
    NSLog(@"開始游泳.");
}
@end

//Bird.h的代碼
#import <Foundation/Foundation.h>

@interface Bird : NSObject
//飛行
- (void)fly;
@end

//Bird.m的代碼
#import "Bird.h"

@implementation Bird

- (void)fly {
    NSLog(@"開始起飛.");
}
@end

//Monster.h的代碼
#import <Foundation/Foundation.h>

@interface Monster : NSObject
//游泳
- (void)swim;
//飛行
- (void)fly;
@end

//Monster.m的代碼
#import "Monster.h"
#import "Fish.h"
#import "Bird.h"

@interface Monster ()
@property (nonatomic, strong) Fish *fish;
@property (nonatomic, strong) Bird *bird;
@end

@implementation Monster

- (instancetype)init {
    if (self = [super init]) {
        self.fish = [Fish new];
        self.bird = [Bird new];
    }
    return self;
}

- (void)swim {
    [_fish swim];
}

- (void)fly {
    [_bird fly];
}

這樣創(chuàng)建Monster實(shí)例對(duì)象就既可以調(diào)用游泳方法又可以調(diào)用飛行方法了。

    //組合
    Monster *m = [Monster new];
    [m swim];
    [m fly];

第二種：Protocol

使用Protocol來實(shí)現(xiàn)多繼承，因?yàn)镻rotocol只能提供接口，而沒有提供實(shí)現(xiàn)方式，所以這種方法只能實(shí)現(xiàn)接口多繼承。如果只是想多繼承基類的接口，那么遵守多協(xié)議無疑是最好的方法，而既需要多繼承接口，又要多繼承其實(shí)現(xiàn)，那么協(xié)議是無能為力了。
直接上代碼。

//Add.h的代碼
#ifndef Add_h
#define Add_h

@protocol Add <NSObject>

- (int)addA:(int)a b:(int)b;

@end

#endif /* Add_h */

//Sub.h的代碼
#ifndef Sub_h
#define Sub_h

@protocol Sub <NSObject>

- (int)subA:(int)a b:(int)b;

@end
#endif /* Sub_h */

//Mul.h的代碼
#ifndef Mul_h
#define Mul_h

@protocol Mul <NSObject>

- (int)mulA:(int)a b:(int)b;

@end
#endif /* Mul_h */

//Calculator.h的代碼
#import <Foundation/Foundation.h>
#import "Add.h"
#import "Sub.h"
#import "Mul.h"

NS_ASSUME_NONNULL_BEGIN

@interface Calculator : NSObject<Add,Sub,Mul>

@end

NS_ASSUME_NONNULL_END

//Calculator.m的代碼
#import "Calculator.h"

@implementation Calculator

#pragma mark - Add
- (int)addA:(int)a b:(int)b {
    return a+b;
}

#pragma mark - Sub
- (int)subA:(int)a b:(int)b {
    return a-b;
}

#pragma mark - Mul
- (int)mulA:(int)a b:(int)b {
    return a*b;
}
@end

這樣創(chuàng)建Calculator實(shí)例對(duì)象就可以調(diào)用Add、Sub和Mul協(xié)議里面方法了。從而實(shí)現(xiàn)接口多繼承。但是只遵循協(xié)議相當(dāng)于聲明了協(xié)議里的方法，不實(shí)現(xiàn)的話運(yùn)行時(shí)調(diào)用會(huì)報(bào)錯(cuò)unrecognized selector sent to instance xxxxxx.

    //protocol
    int a=8,b=4;
    Calculator *c = [Calculator new];
    NSLog(@"%d+%d=%d",a,b,[c addA:a b:b]);
    NSLog(@"%d-%d=%d",a,b,[c subA:a b:b]);
    NSLog(@"%dx%d=%d",a,b,[c mulA:a b:b]);

第三種：組合+Protocol

下面模擬一個(gè)賣書的，一個(gè)賣衣服的，還有一個(gè)既賣書又賣衣服的經(jīng)銷商。這種方法實(shí)際是使用runtime和Protocol對(duì)第一種方法的延伸和擴(kuò)展。直接上代碼。

//BookProvider.h的代碼
#import <Foundation/Foundation.h>

@protocol BookProviderDelegate <NSObject>

- (void)sellBookWithTitle:(NSString *)title;

@end

//在本類里下面三種方式都可以，效果也不盡相同（可以自己進(jìn)行嘗試）：
//第一種：不遵循BookProviderDelegate，也不是對(duì)相關(guān)方法進(jìn)行聲明。這種情況自己本身實(shí)例不能進(jìn)行相關(guān)方法調(diào)用
//第二種：遵循BookProviderDelegate，這種情況自己本身實(shí)例也可以進(jìn)行相關(guān)方法調(diào)用
//第三種：相關(guān)方法進(jìn)行聲明，這種情況自己本身實(shí)例也可以進(jìn)行相關(guān)方法調(diào)用
@interface BookProvider : NSObject<BookProviderDelegate>//遵循代理

//- (void)sellBookWithTitle:(NSString *)title;

//聲明不實(shí)現(xiàn)不會(huì)在methodlist中找到，所以調(diào)用會(huì)報(bào)錯(cuò) unrecognized selector sent to instance
//methodlist中都是.m中有實(shí)現(xiàn)的方法
- (void)publicMethod;
@end

//BookProvider.m的代碼
#import "BookProvider.h"

@implementation BookProvider

#pragma mark - BookProviderDelegate
- (void)sellBookWithTitle:(NSString *)title {
     NSLog(@"You've bought \"%@\".",title);
}

#pragma mark - 私有方法
- (void)packageBook {
    
}
@end

//ClothProvider.h的代碼
#import <Foundation/Foundation.h>

typedef enum : NSUInteger {
    ClothesSizeSmall = 0,
    ClothesSizeMedium,
    ClothesSizeLarge,
} ClothSize;

@protocol ClothProviderDelegate <NSObject>

- (void)sellClothWithSize:(ClothSize)size;

@end

@interface ClothProvider : NSObject<ClothProviderDelegate>

//- (void)sellClothWithSize:(ClothSize)size;
@end

//ClothProvider.m的代碼
#import "ClothProvider.h"

@implementation ClothProvider

#pragma mark - ClothProviderDelegate
- (void)sellClothWithSize:(ClothSize)size {
    NSString *sizeStr;
    switch (size) {
        case ClothesSizeLarge:
            sizeStr = @"large size";
            break;
        case ClothesSizeMedium:
            sizeStr = @"medium size";
            break;
        case ClothesSizeSmall:
            sizeStr = @"small size";
            break;
        default:
            break;
    }
    NSLog(@"You've bought some clothes of %@.",sizeStr);
}
@end

//DealerProxy.h的代碼
#import <Foundation/Foundation.h>
#import "BookProvider.h"
#import "ClothProvider.h"

@interface DealerProxy : NSProxy<BookProviderDelegate,ClothProviderDelegate>

+ (instancetype )dealerProxy;
@end

//DealerProxy.h的代碼
#import "DealerProxy.h"
#import <objc/runtime.h>

@interface DealerProxy (){
    BookProvider *_bookProvider;
    ClothProvider *_clothProvider;
    //方法map
    NSMutableDictionary *_methodsMap;
}

@end

@implementation DealerProxy

+ (instancetype)dealerProxy {
    return [[DealerProxy alloc] init];
}

- (instancetype)init {
    _bookProvider = [BookProvider new];
    _clothProvider = [ClothProvider new];
    _methodsMap = [NSMutableDictionary dictionary];
    //獲取method并存入_methodsMap中
    [self _registerMethodsWithTarget:_bookProvider];
    [self _registerMethodsWithTarget:_clothProvider];
    return self;
}

#pragma mark - private method
- (void)_registerMethodsWithTarget:(id)target {
    unsigned int numberOfMethods = 0;
    //這里處理的只是針對(duì)對(duì)象方法，類方法沒有處理.注意：這里的方法列表只包含.m中實(shí)現(xiàn)的方法，只聲明的方法不包括在內(nèi)。
    Method *method_list = class_copyMethodList([target class], &numberOfMethods);
    
    for (int i = 0; i < numberOfMethods; i++) {
        Method method = method_list[i];
        SEL sel = method_getName(method);
        NSString *selName = NSStringFromSelector(sel);
        [_methodsMap setObject:target forKey:selName];
    }
    NSLog(@"-->%@",_methodsMap);
    free(method_list);
}

#pragma mark - NSProxy override methods
//消息轉(zhuǎn)發(fā)流程
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    NSString *selName = NSStringFromSelector(sel);
    
    id target = _methodsMap[selName];
    if (target && [target respondsToSelector:sel]) {
        return [target methodSignatureForSelector:sel];
    }else{
        return [super methodSignatureForSelector:sel];
    }
}

//消息轉(zhuǎn)發(fā)流程
- (void)forwardInvocation:(NSInvocation *)invocation {
    SEL sel = invocation.selector;
    NSString *selName = NSStringFromSelector(sel);
    id target = _methodsMap[selName];
    if (target && [target respondsToSelector:sel]) {
        [invocation invokeWithTarget:target];
    }else{
        [super forwardInvocation:invocation];
    }
}
@end

這樣DealerProxy實(shí)例既可以賣書又可以賣衣服了。其中涉及到NSProxy、消息轉(zhuǎn)發(fā)以及runtime相關(guān)知識(shí)大家請(qǐng)自行百度。

    //組合+Protocol
    BookProvider *b = [BookProvider new];
    [b sellBookWithTitle:@"<<從刪庫(kù)到跑路>>"];
    ClothProvider *c = [ClothProvider new];
    [c sellClothWithSize:ClothesSizeLarge];
    DealerProxy *p = [DealerProxy dealerProxy];
    [p sellBookWithTitle:@"Object C"];
    [p sellClothWithSize:ClothesSizeMedium];