AFNetworking源码解析

AFNetworking 网络请求使用

天气网络请求

    AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc]initWithBaseURL:[NSURL URLWithString:@"http://www.sojson.com"]];
    [manager GET:@"/open/api/weather/json.shtml" parameters:@{@"city":@"北京"} progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
        NSLog(@"%@", responseObject);
    } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
        NSLog(@"%@", error);
    }];

从初始化AFHTTPSessionManager方法得到以下调用栈

- [AFHTTPSessionManager initWithBaseURL:]
    - [AFHTTPSessionManager initWithBaseURL:sessionConfiguration:]
        - [AFURLSessionManager initWithSessionConfiguration:]
            - [NSURLSession sessionWithConfiguration:delegate:delegateQueue:]
            - [AFJSONResponseSerializer serializer] // 负责序列化响应
            - [AFSecurityPolicy defaultPolicy] // 负责身份认证
            - [AFNetworkReachabilityManager sharedManager] // 查看网络连接情况
        - [AFHTTPRequestSerializer serializer] // 负责序列化请求
        - [AFJSONResponseSerializer serializer] // 负责序列化响应

可以看出AFHTTPSessionManager继承AFURLSessionManager
针对于HTTP快速创建请求GET、POST等

AFNetworking 整体框架

af2.png

查看 -GET:parameter:process:success:failure:调用栈

- [AFHTTPSessionManager GET:parameters:process:success:failure:]
    - [AFHTTPSessionManager dataTaskWithHTTPMethod:parameters:uploadProgress:downloadProgress:success:failure:] // 返回 NSURLSessionDataTask #1
        - [AFHTTPRequestSerializer requestWithMethod:URLString:parameters:error:] // 返回 NSMutableURLRequest
        - [AFURLSessionManager dataTaskWithRequest:uploadProgress:downloadProgress:completionHandler:] // 返回 NSURLSessionDataTask #2
            - [NSURLSession dataTaskWithRequest:] // 返回 NSURLSessionDataTask #3
            - [AFURLSessionManager addDelegateForDataTask:uploadProgress:downloadProgress:completionHandler:]
                - [AFURLSessionManagerTaskDelegate init]
                - [AFURLSessionManager setDelegate:forTask:]
    - [NSURLSessionDataTask resume]

AFURLSessionManager 介绍

 `AFURLSessionManager` creates and manages an `NSURLSession` object based on a specified `NSURLSessionConfiguration` object, which conforms to ``, ``, ``, and ``.

1.负责创建和管理NSURLSession
2.管理NSURLSessionTask
3.实现NSURLSession中各种代理协议
4.引入AFSecurityPolicy保证请求的安全
5.引入AFNetworkingReachabilityManager监控网络状态

AFURLSessionManager 初始化方法
- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
    self = [super init];
    if (!self) {
        return nil;
    }

    if (!configuration) {
        configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    }

    self.sessionConfiguration = configuration;

    self.operationQueue = [[NSOperationQueue alloc] init];
    self.operationQueue.maxConcurrentOperationCount = 1;

    self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];

    self.responseSerializer = [AFJSONResponseSerializer serializer];

    self.securityPolicy = [AFSecurityPolicy defaultPolicy];

#if !TARGET_OS_WATCH
    self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
#endif

    self.mutableTaskDelegatesKeyedByTaskIdentifier = [[NSMutableDictionary alloc] init];

    self.lock = [[NSLock alloc] init];
    self.lock.name = AFURLSessionManagerLockName;

    [self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
        for (NSURLSessionDataTask *task in dataTasks) {
            [self addDelegateForDataTask:task uploadProgress:nil downloadProgress:nil completionHandler:nil];
        }

        for (NSURLSessionUploadTask *uploadTask in uploadTasks) {
            [self addDelegateForUploadTask:uploadTask progress:nil completionHandler:nil];
        }

        for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
            [self addDelegateForDownloadTask:downloadTask progress:nil destination:nil completionHandler:nil];
        }
    }];

    return self;
}

AFURLSessionManager实例化后，创建NSURLSessionData实例，方法包括

/**
 Creates an `NSURLSessionDataTask` with the specified request.

 @param request The HTTP request for the request.
 @param completionHandler A block object to be executed when the task finishes. This block has no return value and takes three arguments: the server response, the response object created by that serializer, and the error that occurred, if any.
 */
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                            completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler;

/**
 Creates an `NSURLSessionDataTask` with the specified request.

 @param request The HTTP request for the request.
 @param uploadProgressBlock A block object to be executed when the upload progress is updated. Note this block is called on the session queue, not the main queue.
 @param downloadProgressBlock A block object to be executed when the download progress is updated. Note this block is called on the session queue, not the main queue.
 @param completionHandler A block object to be executed when the task finishes. This block has no return value and takes three arguments: the server response, the response object created by that serializer, and the error that occurred, if any.
 */
- (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;

具体的调用如下

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                            completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
    return [self dataTaskWithRequest:request uploadProgress:nil downloadProgress:nil completionHandler:completionHandler];
}

- (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;
}

该方法中，AFURLSessionManager调用
[AFURLSessionManager addDelegateForDataTask:uploadProgress:downloadProgress:completionHandler:] 该方法，将completionHandler uploadProgressBlock和downloadProgressBlock传入创建的AFURLSessionManagerTaskDelegate对象中并在相应事件发生时进行回调。
该方法具体实现，处于AFURLSessionManager.M文件中

- (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] init];
    delegate.manager = self;
    delegate.completionHandler = completionHandler;

    dataTask.taskDescription = self.taskDescriptionForSessionTasks;
    [self setDelegate:delegate forTask:dataTask];

    delegate.uploadProgressBlock = uploadProgressBlock;
    delegate.downloadProgressBlock = downloadProgressBlock;
}

通过调用 - [AFURLSessionManager setDelegate:forTask:]来设置代理：

- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
            forTask:(NSURLSessionTask *)task
{
    NSParameterAssert(task);
    NSParameterAssert(delegate);

    [self.lock lock];
    self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
    [delegate setupProgressForTask:task];
    [self addNotificationObserverForTask:task];
    [self.lock unlock];
}

可以看出，AFURLSessionManager通过字典mutableTaskDelegatesKeyedByTaskIdentifier 来存储和管理每个NSURLSessionTask，以taskIdentifier为key值。

查看AFURLSessionManager中实现的各种代理包括：

NSURLSessionDelegate
NSURLSessionTaskDelegate
NSURLSessionDataDelegate
NSURLSessionDownDelegate

将NSURLSession的代理指向AFURLSessionManager的代码

self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];

NSURLSessionDelegate 对应的方法

/*
 * Messages related to the URL session as a whole
 */
@protocol NSURLSessionDelegate 
@optional

/* The last message a session receives.  A session will only become
 * invalid because of a systemic error or when it has been
 * explicitly invalidated, in which case the error parameter will be nil.
 */
- (void)URLSession:(NSURLSession *)session didBecomeInvalidWithError:(nullable NSError *)error;

/* If implemented, when a connection level authentication challenge
 * has occurred, this delegate will be given the opportunity to
 * provide authentication credentials to the underlying
 * connection. Some types of authentication will apply to more than
 * one request on a given connection to a server (SSL Server Trust
 * challenges).  If this delegate message is not implemented, the 
 * behavior will be to use the default handling, which may involve user
 * interaction. 
 */
- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
                                             completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler;

/* If an application has received an
 * -application:handleEventsForBackgroundURLSession:completionHandler:
 * message, the session delegate will receive this message to indicate
 * that all messages previously enqueued for this session have been
 * delivered.  At this time it is safe to invoke the previously stored
 * completion handler, or to begin any internal updates that will
 * result in invoking the completion handler.
 */
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session API_AVAILABLE(ios(7.0), watchos(2.0), tvos(9.0)) API_UNAVAILABLE(macos);

通过实现该代理，再执行AFURLSessionManager实现的Block。

例如AFURLSessionManager 暴露的方法

/**
 Sets a block to be executed when the managed session becomes invalid, as handled by the `NSURLSessionDelegate` method `URLSession:didBecomeInvalidWithError:`.

 @param block A block object to be executed when the managed session becomes invalid. The block has no return value, and takes two arguments: the session, and the error related to the cause of invalidation.
 */
- (void)setSessionDidBecomeInvalidBlock:(nullable void (^)(NSURLSession *session, NSError *error))block;

/**
 Sets a block to be executed when a connection level authentication challenge has occurred, as handled by the `NSURLSessionDelegate` method `URLSession:didReceiveChallenge:completionHandler:`.

 @param block A block object to be executed when a connection level authentication challenge has occurred. The block returns the disposition of the authentication challenge, and takes three arguments: the session, the authentication challenge, and a pointer to the credential that should be used to resolve the challenge.
 */
- (void)setSessionDidReceiveAuthenticationChallengeBlock:(nullable NSURLSessionAuthChallengeDisposition (^)(NSURLSession *session, NSURLAuthenticationChallenge *challenge, NSURLCredential * _Nullable __autoreleasing * _Nullable credential))block;

AFURLSession中NSURLSessionDelegate的实现

#pragma mark - NSURLSessionDelegate

- (void)URLSession:(NSURLSession *)session
didBecomeInvalidWithError:(NSError *)error
{
    if (self.sessionDidBecomeInvalid) {
        self.sessionDidBecomeInvalid(session, error);
    }

    [[NSNotificationCenter defaultCenter] postNotificationName:AFURLSessionDidInvalidateNotification object:session];
}

AFURLSessionManager 中AFURLSessionManagerTaskDelegate代理管理task进度并在结束时进行回调。

主要方法

- (void)setupProgressForTask:(NSURLSessionTask *)task

该方法的主要作用
1.设置uploadProgress，downloadProgress回调代码
2.添加KVO 对task中NSProgress中属性进行键值观测

AFURLSessionManagerTaskDelegate 中实现的 NSURLSessionTaskDelegate代理方法

- (void)URLSession:(__unused NSURLSession *)session
              task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error

具体实现可参照该框架

- (void)URLSession:(__unused NSURLSession *)session
              task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error  
{
    #1：获取数据, 存储 `responseSerializer` 和 `downloadFileURL`
    if (error) {
        #2：在存在错误时调用 `completionHandler`
    } else {
        #3：调用 `completionHandler`
    }
}

AFNetWorking 总结

AFURLSessionManager是对NSURLSession的封装
它通过- [AFURLSessionManager dataTaskWithRequest:completionHandler:]等接口创建NSURLSessionDataTask的实例
持有一个字典mutableTaskDelegatesKeyedByTaskIdentifier管理这些data task 实例
引入AFURLSessionManagerTaskDelegate来对传入的uploadProgressBlock downloadProgressBlock completionHandler 在合适的时间进行调用
实现了全部的代理方法来提供block接口
通过方法调用在data task 状态改变时，发出通知