研读CTMediator 源码

iOS Runtime 模块化设计：降低组件耦合

最新推荐文章于 2024-04-19 11:21:51 发布

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本文介绍了如何通过Runtime在iOS中实现模块间的低耦合调用。主要涉及两个核心方法：1) 本地组件调用入口，用于生成Target并执行Action；2) 安全的消息转发实现，确保Target-Action方法的安全执行。通过动态生成Target和Action字符串，以及判断Target是否响应Action，实现了模块间的解耦通信。在无响应时，提供了备用处理机制。

原理基于Runtime 实现模块Targe_模块-Action_方法实现可以让不同模块之间耦合度降低

两个核心方法

1。本地组件调用入口 - (id _Nullable )performTarget:(NSString * _Nullable)targetName action:(NSString * _Nullable)actionName params:(NSDictionary * _Nullable)params

- (id)performTarget:(NSString *)targetName action:(NSString *)actionName params:(NSDictionary *)params shouldCacheTarget:(BOOL)shouldCacheTarget
{
    if (targetName == nil || actionName == nil) {
        return nil;
    }
    
    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];
    }
    NSObject *target = [self safeFetchCachedTarget:targetClassString];
    if (target == nil) {
        Class targetClass = NSClassFromString(targetClassString);
        target = [[targetClass alloc] init];
    }

    // generate action
    NSString *actionString = [NSString stringWithFormat:@"Action_%@:", actionName];
    SEL action = NSSelectorFromString(actionString);
    
    if (target == nil) {
        // 这里是处理无响应请求的地方之一，这个demo做得比较简单，如果没有可以响应的target，就直接return了。实际开发过程中是可以事先给一个固定的target专门用于在这个时候顶上，然后处理这种请求的
        [self NoTargetActionResponseWithTargetString:targetClassString selectorString:actionString originParams:params];
        return nil;
    }
    
    if (shouldCacheTarget) {
        [self safeSetCachedTarget:target key:targetClassString];
    }

    if ([target respondsToSelector:action]) {
        return [self safePerformAction:action target:target params:params];
    } else {
        // 这里是处理无响应请求的地方，如果无响应，则尝试调用对应target的notFound方法统一处理
        SEL action = NSSelectorFromString(@"notFound:");
        if ([target respondsToSelector:action]) {
            return [self safePerformAction:action target:target params:params];
        } else {
            // 这里也是处理无响应请求的地方，在notFound都没有的时候，这个demo是直接return了。实际开发过程中，可以用前面提到的固定的target顶上的。
            [self NoTargetActionResponseWithTargetString:targetClassString selectorString:actionString originParams:params];
            @synchronized (self) {
                [self.cachedTarget removeObjectForKey:targetClassString];
            }
            return nil;
        }
    }
}

分成三步：

001 生成Target

        Class targetClass = NSClassFromString(targetClassString);
        target = [[targetClass alloc] init];

002 根据规则生成Action

    NSString *actionString = [NSString stringWithFormat:@"Action_%@:", actionName];
    SEL action = NSSelectorFromString(actionString);

003 判断target是否可以响应 action那么Target 去执行Action

  if ([target respondsToSelector:action]) {
        return [self safePerformAction:action target:target params:params];
    }

2。安全实现 Targe_模块-Action_方法消息转发

- (id)safePerformAction:(SEL)action target:(NSObject *)target params:(NSDictionary *)params
{
    NSMethodSignature* methodSig = [target methodSignatureForSelector:action];
    if(methodSig == nil) {
        return nil;
    }
    const char* retType = [methodSig methodReturnType];

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

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    return [target performSelector:action withObject:params];
#pragma clang diagnostic pop
}

第一步判断方法签名

第二步判断方法返回类型根据返回类型进行手动组装方法调用

最后一步才开始动态执行target-action