AFNetworking是封装的NSURLSession的网络请求，由五个模块组成：分别由NSURLSession,Security,Reachability,Serialization,UIKit五部分组成
NSURLSession：网络通信模块（核心模块） 对应 AFNetworking中的 AFURLSessionManager和对HTTP协议进行特化处理的 AFHTTPSessionManager,AFHTTPSessionManager是继承于AFURLSessionmanager的
Security：网络通讯安全策略模块 对应 AFSecurityPolicy
Reachability：网络状态监听模块 对应AFNetworkReachabilityManager
Serialization：网络通信信息序列化、反序列化模块 对应 AFURLResponseSerialization
UIKit：对于iOS UIKit的扩展库
创建
AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
其内部方法最终调用
- (instancetype)initWithBaseURL:(NSURL *)url方法来初始化AFHTTPSessionManager
- (instancetype)initWithBaseURL:(NSURL *)url
sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
self = [super initWithSessionConfiguration:configuration];
if (!self) {
return nil;
}
// Ensure terminal slash for baseURL path, so that NSURL +URLWithString:relativeToURL: works as expected
if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
url = [url URLByAppendingPathComponent:@""];
}
self.baseURL = url;
//初始化
self.requestSerializer = [AFHTTPRequestSerializer serializer];
self.responseSerializer = [AFJSONResponseSerializer serializer];
return self;
}
该方法同时初始化了requestSerializer和responseSerializer
之后在进行网络请求时，会调用GET或POST方法，这里用POST举例
[manager POST:@"" parameters:nil progress:nil success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
NSLog(@"success");
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
NSLog(@"failure");
}];
内部实现方法为：
- (NSURLSessionDataTask *)POST:(NSString *)URLString
parameters:(id)parameters
progress:(void (^)(NSProgress * _Nonnull))uploadProgress
success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{
NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"POST" URLString:URLString parameters:parameters uploadProgress:uploadProgress downloadProgress:nil success:success failure:failure];
[dataTask resume];
return dataTask;
}
这里是使用的dataTaskWithHTTPMethod方法新建了一个NSURLSessionDataTask任务，然后执行它。
dataTaskWithHTTPMethod方法的内部原理:
- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
URLString:(NSString *)URLString
parameters:(id)parameters
uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
success:(void (^)(NSURLSessionDataTask *, id))success
failure:(void (^)(NSURLSessionDataTask *, NSError *))failure
{
//1.1新建一个NSMutableURLRequest
NSError *serializationError = nil;
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
//1.2判断是否新建成功
if (serializationError) {
if (failure) {
dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
failure(nil, serializationError);
});
}
return nil;
}
//2.1新建NSURLSessionDataTask
//这个dataTask需要回调给外部,所以需要__block修饰
__block NSURLSessionDataTask *dataTask = nil;
dataTask = [self dataTaskWithRequest:request
uploadProgress:uploadProgress
downloadProgress:downloadProgress
completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
//2.2设置回调
if (error) {
if (failure) {
failure(dataTask, error);
}
} else {
if (success) {
success(dataTask, responseObject);
}
}
}];
return dataTask;
}
这里可以分两部分看，第一部分是创建一个NSMutableURLRequest，创建成功进行下一步，创建失败则回调failure(nil, serializationError);方法，创建NSMutableURLRequest：
- (NSMutableURLRequest *)requestWithMethod:(NSString *)method
URLString:(NSString *)URLString
parameters:(id)parameters
error:(NSError *__autoreleasing *)error
{
//检验参数的完整性
NSParameterAssert(method);
NSParameterAssert(URLString);
NSURL *url = [NSURL URLWithString:URLString];
NSParameterAssert(url);
//新建一个NSMutableURLRequest，设置起请求类型
NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
mutableRequest.HTTPMethod = method;
//循环遍历给mutableRequest设置参数
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
[mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
}
}
//将传入的parameters进行编码，并添加到request中
//不同的请求格式内部调用方法不一样（AFHTTPRequestSerializer，AFJSONRequestSerializer，AFPropertyListRequestSerializer）
mutableRequest = [[self requestBySerializingRequest:mutableRequest withParameters:parameters error:error] mutableCopy];
return mutableRequest;
}
当NSMutableURLRequest创建成功时，进入第二步，新建一个NSURLSessionDataTask，设置failure和success的回调函数，然后返回新建的NSURLSessionDataTask，新建NSURLSessionDataTask的方法内部实现：
- (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;
}
使用了url_session_manager_create_task_safely(dispatch_block_t block)这个函数。这个函数主要的目的是为了解决iOS8之前的一个bug
新建一个NSURLSessionDataTask，在url_session_manager_create_task_safely中初始化，然后用addDelegateForDataTask方法添加代理，最后返回该dataTask，添加代理的具体内部实现：
- (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;
}
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