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@CoDancer 2018-04-30T12:56:24.000000Z 字数 7154 阅读 899

AFNetworking 底部代码的阅读笔记

网络 数据请求

先从AFNetworking框架从上往下看，可以看到它的对外接口主要有：

  1. - (NSURLSessionDataTask *)GET:(NSString *)URLString
  2.                    parameters:(id)parameters
  3.                      progress:(void (^)(NSProgress * _Nonnull))downloadProgress
  4.                       success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
  5.                       failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
当然这是通过AFHTTPSessionManager的对象去调用，返回的是NSURLSessionDataTask，在这个方法中，我们需要关心的有两个地方，一个是block事件的数据返回，一个是return返回的NSURLSessionDataTask的对象。

再往下面看一层是：

  1. - (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
  2.                                        URLString:(NSString *)URLString
  3.                                       parameters:(id)parameters
  4.                                   uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
  5.                                 downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
  6.                                          success:(void (^)(NSURLSessionDataTask *, id))success
  7.                                          failure:(void (^)(NSURLSessionDataTask *, NSError *))failure

在这个方法中有：

  1. NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];

创建可改变的网络请求，在这个请求中设置

  1. NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
  2.     mutableRequest.HTTPMethod = method;

并且设置请求对象中头部字段HTTPHeaderField

  1. [self setValue:[acceptLanguagesComponents componentsJoinedByString:@", "] forHTTPHeaderField:@"Accept-Language"];
  3.     NSString *userAgent = nil;
  4. #if TARGET_OS_IOS
  5.     // User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
  6.     userAgent = [NSString stringWithFormat:@"%@/%@ (%@; iOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[UIDevice currentDevice] model], [[UIDevice currentDevice] systemVersion], [[UIScreen mainScreen] scale]];
  1. >_mutableHTTPRequestHeaders:
  2. {
  3.     "Accept-Language" = "en;q=1";
  4.     "User-Agent" = "iOS Example/1.0 (iPhone; iOS 11.2; Scale/2.00)";
  5. }

初始化好网络请求对象后，然后把它当作参数传到方法中。

  1. - (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
  2.                                uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
  3.                              downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
  4.                             completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler {
  6.     __block NSURLSessionDataTask *dataTask = nil;
  7.     url_session_manager_create_task_safely(^{
  8.         dataTask = [self.session dataTaskWithRequest:request];
  9.     });
  11.     [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
  13.     return dataTask;
  14. }

当然这个方法中返回的还是NSURLSessionDataTask的对象，但我们需要看的是block中的处理。
在这个方法中主要有两个通知

  1. - (void)addNotificationObserverForTask:(NSURLSessionTask *)task {
  2.     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskDidResume:) name:AFNSURLSessionTaskDidResumeNotification object:task];
  3.     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskDidSuspend:) name:AFNSURLSessionTaskDidSuspendNotification object:task];
  4. }

监听恢复网络连接和暂停的事件。
而在创建AFHTTPSessionManager对象是的方法中有：

  1. - (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration

这里面主要有

  1. self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];
  3. [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
  4.         for (NSURLSessionDataTask *task in dataTasks) {
  5.             [self addDelegateForDataTask:task uploadProgress:nil downloadProgress:nil completionHandler:nil];
  6.         }
  8.         for (NSURLSessionUploadTask *uploadTask in uploadTasks) {
  9.             [self addDelegateForUploadTask:uploadTask progress:nil completionHandler:nil];
  10.         }
  12.         for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
  13.             [self addDelegateForDownloadTask:downloadTask progress:nil destination:nil completionHandler:nil];
  14.         }
  15.     }];

当然我们终于快看到了数据交接的底部了，就是AFURLSessionManager对象实现了 协议中的方法，而在实现这些方法中（举一个例子说明）

  1. - (void)URLSession:(NSURLSession *)session
  2.               task:(NSURLSessionTask *)task
  3. didCompleteWithError:(NSError *)error
  4. {
  5.     AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];
  7.     // delegate may be nil when completing a task in the background
  8.     if (delegate) {
  9.         [delegate URLSession:session task:task didCompleteWithError:error];
  11.         [self removeDelegateForTask:task];
  12.     }
  14.     if (self.taskDidComplete) {
  15.         self.taskDidComplete(session, task, error);
  16.     }
  17. }

这个时候创建了一个AFURLSessionManagerTaskDelegate的对象，当然这个对象也实现了那些代理，而在这个类中，与原生IOS交接的方法中

  1. - (void)URLSession:(__unused NSURLSession *)session
  2.               task:(NSURLSessionTask *)task
  3. didCompleteWithError:(NSError *)error
  5. dispatch_async(url_session_manager_processing_queue(), ^{
  6.             NSError *serializationError = nil;
  7.             responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:data error:&serializationError];
  9.             if (self.downloadFileURL) {
  10.                 responseObject = self.downloadFileURL;
  11.             }
  13.             if (responseObject) {
  14.                 userInfo[AFNetworkingTaskDidCompleteSerializedResponseKey] = responseObject;
  15.             }
  17.             if (serializationError) {
  18.                 userInfo[AFNetworkingTaskDidCompleteErrorKey] = serializationError;
  19.             }
  21.             dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
  22.                 if (self.completionHandler) {
  23.                     self.completionHandler(task.response, responseObject, serializationError);
  24.                 }
  26.                 dispatch_async(dispatch_get_main_queue(), ^{
  27.                     [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
  28.                 });
  29.             });
  30.         });

这里我们看到dispatch_group_async

而它的作用是：可以实现监听一组任务是否完成，完成后得到通知执行其他的操作。

void dispatch_group_async(dispatch_group_t group,
                      dispatch_queue_t queue,
                      dispatch_block_t block);

group： 对应的任务组
queue： block任务执行的线程队列

在AFURLSessionManager对象中完成了队列后，就会获取主线程并把需要的数据通过回调传出去，当然也会通知这个任务完成的通知。

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkRequestDidFinish:) name:AFNetworkingTaskDidCompleteNotification object:nil];

  1. - (void)networkRequestDidFinish:(NSNotification *)notification {
  2.     if ([AFNetworkRequestFromNotification(notification) URL]) {
  3.         [self decrementActivityCount];
  4.     }
  5. }

这样就完成了数据的获取和回调。

NSURLSessionDataTaskAFHTTPSessionManagerAFURLSessionManagerAFURLSessionManagerTaskDelegatecompletionHandlerAFHTTPSessionManager
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