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三、AFNetworking使用的代码分析
3.3 AFHTTPSessionManager GET: parameters: headers: progress: success: failure: 方法
AFHTTPSessionManager GET: parameters: headers: progress: success: failure: 方法调用栈
3.3.1 NSURLSessionTask
这里引入了一个新的类：NSURLSessionDataTask。NSURLSessionDataTask继承了NSURLSessionTask。** NSURLSessionTask**的官方说明：
The NSURLSessionTask class is the base class for tasks in a URL session. Tasks are always part of a session; you create a task by calling one of the task creation methods on an NSURLSession object. The method you call determines the type of task.
URL sessions provide three types of tasks: data tasks, upload tasks, and download tasks. These tasks are instances of the NSURLSessionDataTask, NSURLSessionUploadTask, NSURLSessionDownloadTask, NSURLSessionStreamTask subclasses of NSURLSessionTask, respectively.
简单罗列以下两点：
1.NSURLSessionTask是官方提供的几种网络任务类的基类； 2.官方提供了三种任务处理的子类：简单数据处理任务类、上传任务类和下载任务类。
3.3.2 AFHTTPSessionManager dataTaskWithHTTPMethod:...方法实现与分析
- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
URLString:(NSString *)URLString
parameters:(id)parameters
headers:(NSDictionary<NSString *,NSString *> *)headers
uploadProgress:(void (^)(NSProgress * _Nonnull))uploadProgress
downloadProgress:(void (^)(NSProgress * _Nonnull))downloadProgress
success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure {
NSError *serializationError = nil;
// 1.通过全局配置的requestSerializer初始化一个请求的实例
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
for (NSString *headerField in headers.keyEnumerator) {
[request setValue:headers[headerField] forKey:headerField];
}
if (serializationError) {
if (failure) {
dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
failure(nil, serializationError);
});
}
return nil;
}
// 2.根据请求的实例再初始化一个task的实例
__block NSURLSessionDataTask *dataTask = nil;
dataTask = [self dataTaskWithRequest:request
uploadProgress:uploadProgress
downloadProgress:downloadProgress
completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
if (error) {
if (failure) {
failure(dataTask, error);
}
} else {
if (success) {
success(dataTask, responseObject);
}
}
}];
return dataTask;
}
3.3.3 [AFURLSessionManager addDelegateForDataTask:...]方法，用于task与delegate的绑定
// 1. 根据请求信息初始化一个task实例
- (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 {
NSURLSessionDataTask *dataTask = [self.session dataTaskWithRequest:request];
[self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
return dataTask;
}
- (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
{
// 2.初始化一个任务的代理
AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] initWithTask:dataTask];
delegate.manager = self;
// 此处赋值了请求完成的回调，后续会用到
delegate.completionHandler = completionHandler;
// 3.利用全局的字典存储绑定信息，key为taskID，value为代理的实例。
dataTask.taskDescription = self.taskDescriptionForSessionTasks;
[self setDelegate:delegate forTask:dataTask];
delegate.uploadProgressBlock = uploadProgressBlock;
delegate.downloadProgressBlock = downloadProgressBlock;
}
- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
forTask:(NSURLSessionTask *)task
{
NSParameterAssert(task);
NSParameterAssert(delegate);
[self.lock lock];
// 1.绑定taskID与代理self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
// 2.使用KVO对一些方法监听，返回上传或下载的进度
self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
[self addNotificationObserverForTask:task];
[self.lock unlock];
}
3.3.4 NSURLSessionTaskDelegate协议中的URLSession:task:didCompleteWithError:方法
NSURLSessionTaskDelegate协议包含NSURLSessionDelegate协议
当请求收到了响应后，会触发**- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask )task didCompleteWithError:(nullable NSError )error; 回调（AFURLSessionManager的session属性懒加载时，设置了delegate为self，会触发该代理的方法），以下是方法中的具体处理。
// AFURLSessionManager.m中NSURLSessionTaskDelegate方法的实现，该方法由系统自动触发
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
// 1.根据task获取绑定的代理实例
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];
// delegate may be nil when completing a task in the background
if (delegate) {
// 2.统一处理，调用AFURLSessionManagerTaskDelegate的同名方法。
[delegate URLSession:session task:task didCompleteWithError:error];
[self removeDelegateForTask:task];
}
if (self.taskDidComplete) {
self.taskDidComplete(session, task, error);
}
}
// AFURLSessionManagerTaskDelegate.m中NSURLSessionTaskDelegate方法的实现，该方法在AFURLSessionManager中通过delegate调用。
- (void)URLSession:(__unused NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
error = objc_getAssociatedObject(task, AuthenticationChallengeErrorKey) ?: error;
__strong AFURLSessionManager *manager = self.manager;
__block id responseObject = nil;
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 AF_CAN_USE_AT_AVAILABLE && AF_CAN_INCLUDE_SESSION_TASK_METRICS
if (@available(iOS 10, macOS 10.12, watchOS 3, tvOS 10, *)) {
if (self.sessionTaskMetrics) {
userInfo[AFNetworkingTaskDidCompleteSessionTaskMetrics] = self.sessionTaskMetrics;
}
}
#endif
if (self.downloadFileURL) {
userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;
} else if (data) {
userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;
}
if (error) {
// 1.iOS网络框架返回的错误信息处理
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 {
// 2.请求成功后需要用响应的数据解析类的responseSerializer实例处理返回的数据
// 数据通过NSURLSessionDataDelegate协议的- (void)URLSession:(__unused NSURLSession *)session dataTask:(__unused NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data方法返回
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(), ^{
// 3.绑定task与处理的数据代理时，传入代理的完成的回调
if (self.completionHandler) {
self.completionHandler(task.response, responseObject, serializationError);
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
});
}
}
参考来源：
