前兩篇文章主要是對(duì)這篇文章的內(nèi)容進(jìn)行了一個(gè)鋪墊翠储，這里就一起來(lái)看下 CTMediator 的實(shí)現(xiàn)原理

CTMediator 中最關(guān)鍵的一個(gè)方法：

- (id)performTarget:(NSString *)targetName action:(NSString *)actionNameparams:(NSDictionary *)params shouldCacheTarget:(BOOL)shouldCacheTarget;

看一下里面的具體實(shí)現(xiàn)：

    // 從 params   字典中 獲取 swiftModuleName
    NSString *swiftModuleName = params[kCTMediatorParamsKeySwiftTargetModuleName];
    
    // generate target
    NSString *targetClassString = nil;
    if (swiftModuleName.length > 0) {
        targetClassString = [NSString stringWithFormat:@"%@.Target_%@", swiftModuleName, targetName];
    } else {
        targetClassString = [NSString stringWithFormat:@"Target_%@", targetName];
    }
    // 根據(jù) targetClassString 從 cachedTarget （緩存的Target）獲取 target 
    NSObject *target = self.cachedTarget[targetClassString];
    if (target == nil) {
        // 未獲取到 則生成一個(gè)target
        Class targetClass = NSClassFromString(targetClassString);
        target = [[targetClass alloc] init];
    }

    // generate action
    NSString *actionString = [NSString stringWithFormat:@"Action_%@:", actionName];
    SEL action = NSSelectorFromString(actionString);
    
    if (target == nil) {
        // 這里是處理無(wú)響應(yīng)請(qǐng)求的地方之一，這個(gè)demo做得比較簡(jiǎn)單合搅，如果沒(méi)有可以響應(yīng)的target，就直接return了。實(shí)際開(kāi)發(fā)過(guò)程中是可以事先給一個(gè)固定的target專門(mén)用于在這個(gè)時(shí)候頂上，然后處理這種請(qǐng)求的
        [self NoTargetActionResponseWithTargetString:targetClassString selectorString:actionString originParams:params];
        return nil;
    }
    // 是否需要對(duì) Target 進(jìn)行緩存
    if (shouldCacheTarget) {
        // 將 Target 進(jìn)行緩存
        self.cachedTarget[targetClassString] = target;
    }

    // 判斷 Target 是否有 action 相應(yīng)暂题，避免crash
    if ([target respondsToSelector:action]) {
        // 這里是處理有響應(yīng)請(qǐng)求的地方
        return [self safePerformAction:action target:target params:params];
    } else {
        // 這里是處理無(wú)響應(yīng)請(qǐng)求的地方，如果無(wú)響應(yīng)究珊，則嘗試調(diào)用對(duì)應(yīng)target的notFound方法統(tǒng)一處理
        SEL action = NSSelectorFromString(@"notFound:");
        if ([target respondsToSelector:action]) {
            return [self safePerformAction:action target:target params:params];
        } else {
            // 這里也是處理無(wú)響應(yīng)請(qǐng)求的地方薪者，在notFound都沒(méi)有的時(shí)候，這個(gè)demo是直接return了剿涮。實(shí)際開(kāi)發(fā)過(guò)程中言津，可以用前面提到的固定的target頂上的。
            [self NoTargetActionResponseWithTargetString:targetClassString selectorString:actionString originParams:params];
            // 刪除緩存的無(wú)用 Target
            [self.cachedTarget removeObjectForKey:targetClassString];
            return nil;
        }
    }

處理有響應(yīng)請(qǐng)求的地方會(huì)調(diào)用 - (id)safePerformAction:(SEL)action target:(NSObject *)target params:(NSDictionary *)params 方法

    // NSMethodSignature 該類為對(duì)方法的參數(shù)取试、返回類型進(jìn)行封裝
    NSMethodSignature* methodSig = [target methodSignatureForSelector:action];
    if(methodSig == nil) {
        return nil;
    }
    // 獲取返回類型
    const char* retType = [methodSig methodReturnType];
    // 判斷返回值 類型 
    if (strcmp(retType, @encode(void)) == 0) {
        // 用來(lái)包裝方法和對(duì)應(yīng)的對(duì)象悬槽，它可以存儲(chǔ)方法的名稱，對(duì)應(yīng)的對(duì)象瞬浓，對(duì)應(yīng)的參數(shù)
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
        [invocation setArgument:&params atIndex:2];
        [invocation setSelector:action];
        [invocation setTarget:target];
        // 執(zhí)行NSInvocation對(duì)象中指定對(duì)象的指定方法初婆，并且傳遞指定的參數(shù)
        [invocation invoke];
        return nil;
    }

    if (strcmp(retType, @encode(NSInteger)) == 0) {
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
        [invocation setArgument:&params atIndex:2];
        [invocation setSelector:action];
        [invocation setTarget:target];
        [invocation invoke];
        NSInteger result = 0;
        // 將返回?cái)?shù)據(jù)拷貝到提供的緩存區(qū)（retLoc）內(nèi)
        [invocation getReturnValue:&result];
        return @(result);
    }

    if (strcmp(retType, @encode(BOOL)) == 0) {
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
        [invocation setArgument:&params atIndex:2];
        [invocation setSelector:action];
        [invocation setTarget:target];
        [invocation invoke];
        BOOL result = 0;
        [invocation getReturnValue:&result];
        return @(result);
    }

    if (strcmp(retType, @encode(CGFloat)) == 0) {
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
        [invocation setArgument:&params atIndex:2];
        [invocation setSelector:action];
        [invocation setTarget:target];
        [invocation invoke];
        CGFloat result = 0;
        [invocation getReturnValue:&result];
        return @(result);
    }

    if (strcmp(retType, @encode(NSUInteger)) == 0) {
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSig];
        [invocation setArgument:&params atIndex:2];
        [invocation setSelector:action];
        [invocation setTarget:target];
        [invocation invoke];
        NSUInteger result = 0;
        [invocation getReturnValue:&result];
        return @(result);
    }
    // 利用RunTime 向target對(duì)象傳遞消息，執(zhí)行 target 中 action 的方法猿棉，傳遞參數(shù) params
    return [target performSelector:action withObject:params];

總結(jié)：
CTMediator 的實(shí)現(xiàn)得益于RunTime的存在磅叛，正因?yàn)槿绱宋覀兛梢越怦罡鱾€(gè)模塊，實(shí)現(xiàn)App之間的模塊化萨赁，這應(yīng)該也是很多iOS開(kāi)發(fā)不愿意完全舍棄OC的原因吧弊琴。