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闲扯AFNetworking源码解耦性

闲扯AFNetworking源码解耦性

作者: 大尾巴熊Johnny | 来源:发表于2017-04-01 11:39 被阅读139次

    最近看了下AFNetworking3.0的代码,发现大师写的代码有很多亮点,其中我觉得最可以借鉴的是模块的解耦性。

    解耦性

    应用方使用AF一般只会用到AFHTTPSessionManger类,而这个类只不过是封装了AFURLSessionManger类的方法,所以主要功能的实现都在AFURLSessionManger类。
    AFURLSessionManger类里面是如何解耦的呢?其中最主要的是,定义了一个字典

    @property (readwrite, nonatomic, strong) NSMutableDictionary *mutableTaskDelegatesKeyedByTaskIdentifier;
    

    该mutableTaskDelegatesKeyedByTaskIdentifier的key值为NSURLSessionTask.taskIdentifier(一个NSURLSessionTask任务的id标识),value值为AFURLSessionManagerTaskDelegate。

    而AFURLSessionManager需要实现的NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate代理,主要都是通过mutableTaskDelegatesKeyedByTaskIdentifier字典抛回给AFURLSessionManagerTaskDelegate里去实现,实现完成的值又通过block回调给AFURLSessionManager里面的block。

    具体流程:

    1、 AFURLSessionManager新建一个Task时,把Task与AFURLSessionManagerTaskDelegate通过字典mutableTaskDelegatesKeyedByTaskIdentifier联系起来

    - (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                                   uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
                                 downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                                completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler {
    
        __block NSURLSessionDataTask *dataTask = nil;
        url_session_manager_create_task_safely(^{
            dataTask = [self.session dataTaskWithRequest:request];
        });
    
        [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
    
        return dataTask;
    }
    

    其中关键代码:

    [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
    
    - (void)addDelegateForDataTask:(NSURLSessionDataTask *)dataTask
                    uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
                  downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
                 completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
    {
        AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] initWithTask:dataTask];
        delegate.manager = self;
        delegate.completionHandler = completionHandler;
    
        dataTask.taskDescription = self.taskDescriptionForSessionTasks;
        [self setDelegate:delegate forTask:dataTask];
    
        delegate.uploadProgressBlock = uploadProgressBlock;
        delegate.downloadProgressBlock = downloadProgressBlock;
    }
    

    2、在回调函数中,把需要实现的委托,抛回给AFURLSessionManagerTaskDelegate去实现,抛回后从字典中移除该Task

    - (void)URLSession:(NSURLSession *)session
                  task:(NSURLSessionTask *)task
    didCompleteWithError:(NSError *)error
    {
        AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];
    
        // delegate may be nil when completing a task in the background
        if (delegate) {
            [delegate URLSession:session task:task didCompleteWithError:error];
    
            [self removeDelegateForTask:task];
        }
    
        if (self.taskDidComplete) {
            self.taskDidComplete(session, task, error);
        }
    }
    

    其中关键代码为:

    [delegate URLSession:session task:task didCompleteWithError:error];
    [self removeDelegateForTask:task];
    

    3、AFURLSessionManagerTaskDelegate去实现该委托,实现完成后把结果给self.completionHandler 的block值,从而就把该值传递给了应用层的completionHandler

    - (void)URLSession:(__unused NSURLSession *)session
                  task:(NSURLSessionTask *)task
    didCompleteWithError:(NSError *)error
    {
        __strong AFURLSessionManager *manager = self.manager;
    
        __block id responseObject = nil;
    
        __block NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
        userInfo[AFNetworkingTaskDidCompleteResponseSerializerKey] = manager.responseSerializer;
    
        //Performance Improvement from #2672
        NSData *data = nil;
        if (self.mutableData) {
            data = [self.mutableData copy];
            //We no longer need the reference, so nil it out to gain back some memory.
            self.mutableData = nil;
        }
    
        if (self.downloadFileURL) {
            userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;
        } else if (data) {
            userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;
        }
    
        if (error) {
            userInfo[AFNetworkingTaskDidCompleteErrorKey] = error;
    
            dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
                if (self.completionHandler) {
                    self.completionHandler(task.response, responseObject, error);
                }
    
                dispatch_async(dispatch_get_main_queue(), ^{
                    [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
                });
            });
        } else {
            dispatch_async(url_session_manager_processing_queue(), ^{
                NSError *serializationError = nil;
                responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:data error:&serializationError];
    
                if (self.downloadFileURL) {
                    responseObject = self.downloadFileURL;
                }
    
                if (responseObject) {
                    userInfo[AFNetworkingTaskDidCompleteSerializedResponseKey] = responseObject;
                }
    
                if (serializationError) {
                    userInfo[AFNetworkingTaskDidCompleteErrorKey] = serializationError;
                }
    
                dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
                    if (self.completionHandler) {
                        self.completionHandler(task.response, responseObject, serializationError);
                    }
    
                    dispatch_async(dispatch_get_main_queue(), ^{
                        [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
                    });
                });
            });
        }
    }
    

    其中关键代码为

    if (self.completionHandler) {
         self.completionHandler(task.response, responseObject, error);
    }
    

    总结

    其实就是把需要实现的Delegate值交给一个类去实现,好处是避免了随着业务不断发展出现回调函数里代码过长,而且直观性比较强,可以在我们工作中借鉴这种写法。最后,如果想看关于AF较为详细的源码分析,可以推荐看看这篇文章:
    《AFNetworking到底做了什么》

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