AFNetworking相关(一)

AFURLSessionManager/AFHTTPSessionManager解析

AFN结构

• AFNetworking
• 核心
  • AFURLSessionManager
  • AFHTTPSessionManager
• 序列化
  • AFURLRequestSerialization
  • AFHTTPSerializer
  • AFJSONRequestSerializer
  • AFPropertyRequestSerializer
  • AFURLResponseSerialization
  • AFHTTPResponseSerializer
  • AFJSONResponseSerializer
  • AFXMLParserResponseSerializer
  • AFXMLDocumentResponseSerializer(macOS)
  • AFPropertyListResponseSrializer
  • AFImageResponseSerializer
  • AFCompoundResponseSerializer
• 辅助类
  • AFSecurityPolicy
  • AFNetworkReachabilityManager
  • UI类
  • ...

AFHTTPSessionManager的初始化

注意此方法是工厂方法，而不是单例，只看外层写法容易误解
AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];

AFHTTPSessionManager初始化的内部流程

• 1.层层调用至父类(AFURLSessionManager)的初始化方法 - (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration;
• 获取或创建默认configuration并持有

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

• 初始化串行队列(serial queue，苹果文档要求，为了确保回调顺序正确)，用于生成session

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

• 初始化session并持有,session会产生不止一个task

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

• 设置解析(默认JSON)，证书(默认无条件信任https)，网络状态监听

self.responseSerializer = [AFJSONResponseSerializer serializer];
self.securityPolicy = [AFSecurityPolicy defaultPolicy];
self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];

• 初始化一个NSMutableDictionary,用于存储绑定task和delegate(@{key:delegate]})

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

• 初始化线程锁

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

• 异步获取当前session所有未完成task(如从后台回来后初始化session，可能会有之前的任务)

[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];
    }
}];

• 2.处理url，给url拼接"/"

if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
    url = [url URLByAppendingPathComponent:@""];
}

• 3.持有baseURL

self.baseURL = url;

• 4.设置序列化默认值

self.requestSerializer = [AFHTTPRequestSerializer serializer];
self.responseSerializer = [AFJSONResponseSerializer serializer];

发起请求,生成NSURLSessionDataTask

• 生成request

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

• 生成NSMutableURLRequest并设置请求方式

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

• 遍历mutableObservedChangedKeyPaths，给mutableRequest进行KVC赋值
  • 在requestSerializer初始化时，会对mutableObservedChangedKeyPaths进行KVO操作

for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
    if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
        [mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
    }
}

• 将参数进行编码并传递给mutableRequest

mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];

• 执行拷贝

NSMutableURLRequest *mutableRequest = [request mutableCopy];

• 设置请求头

[self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
    if (![request valueForHTTPHeaderField:field]) {
        [mutableRequest setValue:value forHTTPHeaderField:field];
    }
}];

• 将参数字典转为字符串，支持自定义解析方式

1.先通过递归NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value)获得AFQueryStringPair参数数组
2.然后遍历参数数组对AFQueryStringPair进行URLEncodedStringValue百分号编码操作
3.最后对AFQueryStringPair参数数组进行componentsJoinedByString:@"&"元素分割 获得AFQueryStringFromParameters参数字符串

NSString * AFQueryStringFromParameters(NSDictionary *parameters) {
    NSMutableArray *mutablePairs = [NSMutableArray array];
    for (AFQueryStringPair *pair in AFQueryStringPairsFromDictionary(parameters)) {
        [mutablePairs addObject:[pair URLEncodedStringValue]];
    }
    return [mutablePairs componentsJoinedByString:@"&"];
}

NSArray * AFQueryStringPairsFromDictionary(NSDictionary *dictionary) {
    return AFQueryStringPairsFromKeyAndValue(nil, dictionary);
}

NSArray * AFQueryStringPairsFromKeyAndValue(NSString *key, id value) {
    NSMutableArray *mutableQueryStringComponents = [NSMutableArray array];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"description" ascending:YES selector:@selector(compare:)];
    if ([value isKindOfClass:[NSDictionary class]]) {
        NSDictionary *dictionary = value;
        for (id nestedKey in [dictionary.allKeys sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
            id nestedValue = dictionary[nestedKey];
            if (nestedValue) {
                [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue((key ? [NSString stringWithFormat:@"%@[%@]", key, nestedKey] : nestedKey), nestedValue)];
            }
        }
    } else if ([value isKindOfClass:[NSArray class]]) {
        NSArray *array = value;
        for (id nestedValue in array) {
            [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue([NSString stringWithFormat:@"%@[]", key], nestedValue)];
        }
    } else if ([value isKindOfClass:[NSSet class]]) {
        NSSet *set = value;
        for (id obj in [set sortedArrayUsingDescriptors:@[ sortDescriptor ]]) {
            [mutableQueryStringComponents addObjectsFromArray:AFQueryStringPairsFromKeyAndValue(key, obj)];
        }
    } else {
        [mutableQueryStringComponents addObject:[[AFQueryStringPair alloc] initWithField:key value:value]];
    }
    return mutableQueryStringComponents;
}

• 若是GET,HEAD,DELETE请求，将参数拼接到url后面，若是PUT,POST请求，先判断是否有设置Content-Type，未设置则设置为默认值application/x-www-form-urlencoded,然后将参数拼接到http body中

if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
    if (query && query.length > 0) {
        mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
    }
} else {
    if (!query) {
        query = @"";
    }
    if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
        [mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
    }
    [mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
}

• 通过request生成task
• 1.使用串行队列创建dtaTask，解决iOS8以下的一个bug，详情见issue 2093

__block NSURLSessionDataTask *dataTask = nil;
url_session_manager_create_task_safely(^{
dataTask = [self.session dataTaskWithRequest:request];

});

• 给task添加代理

[self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];

• 以taskId为key将delegate存入mutableTaskDelegatesKeyedByTaskIdentifier，每个task都有自己的delegate
  • manager > session > task <> delegate > manager(weak，防止循环引用)
  • manager持有task，task和delegate是绑定的，相当于manager是持有delegate的
  • 用KVO监听AFURLSessionManagerTaskDelegate的downloadProgress和uploadProgress
  • 用KVO监听Task的progress，将监听到的completedUnitCount和totalUnitCount赋给downloadProgress和uploadProgress
  • 监听到downloadProgress和uploadProgress的变化，调用AFURLSessionManagerTaskDelegate的downloadProgressBlock和uploadProgressBlock回调
• resume()
  • task的resume()被替换为af_resume()

- (void)af_resume {
    NSAssert([self respondsToSelector:@selector(state)], @"Does not respond to state");
    NSURLSessionTaskState state = [self state];
    [self af_resume];
    if (state != NSURLSessionTaskStateRunning) {
        [[NSNotificationCenter defaultCenter] postNotificationName:AFNSURLSessionTaskDidResumeNotification object:self];
    }
}

• 当task状态发生改变时，通知到manager

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

• manager发布task状态改变的广播

- (void)taskDidResume:(NSNotification *)notification {
    NSURLSessionTask *task = notification.object;
    if ([task respondsToSelector:@selector(taskDescription)]) {
        if ([task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]) {
            dispatch_async(dispatch_get_main_queue(), ^{
                [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidResumeNotification object:task];
            });
        }
    }
}