AFNetworking 2.x 阅读笔记（一）

AFHTTPRequestOperationManager 接口文件，以及调用流程

AFNetworking 源码根据文件夹划分成5个部分：NSURLConnetion, NSURLSession, Security, Reachability, Serialization。乳沟

首先关注下整个文件的接口类AFHTTPRequestOperationManager类，从调用方法入手

1 POST/GET 方法使用流程

一般会直接使用AFHTTPRequestOperationManager, 直接贴官方的调用流程如下：

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:@"http://example.com/resources.json" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"JSON: %@", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
}];

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
NSDictionary *parameters = @{@"foo": @"bar"};
[manager POST:@"http://example.com/resources.json" parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"JSON: %@", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"Error: %@", error);
}];

...

2 manager主要完成的工作

manager 在指定 init方法中，主要完成了以下初始化，这些属性主要反应了manager主要做的工作

self.baseURL = url; //设定baseURL
self.requestSerializer = [AFHTTPRequestSerializer serializer]; //初始化RequestSerializer
self.responseSerializer = [AFJSONResponseSerializer serializer];//初始化responseSerializer，默认位JSON解析器
self.securityPolicy = [AFSecurityPolicy defaultPolicy];//设置安全策略
self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
self.operationQueue = [[NSOperationQueue alloc] init];//初始化一个OperationQueue
self.shouldUseCredentialStorage = YES;

生成manager 以后，就可以调用 GET/POST 方法：

- (AFHTTPRequestOperation *)GET:(NSString *)URLString
                     parameters:(id)parameters
                        success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                        failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
    AFHTTPRequestOperation *operation = [self HTTPRequestOperationWithHTTPMethod:@"GET" URLString:URLString parameters:parameters success:success failure:failure];

    [self.operationQueue addOperation:operation];

    return operation;
}

- (AFHTTPRequestOperation *)POST:(NSString *)URLString
                      parameters:(id)parameters
                         success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                         failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
    AFHTTPRequestOperation *operation = [self HTTPRequestOperationWithHTTPMethod:@"POST" URLString:URLString parameters:parameters success:success failure:failure];

    [self.operationQueue addOperation:operation];

    return operation;
}

POST/GET两者在请求过程中方法都一样，都是生成一个AFHTTPRequestOperation对象，然后添加到前面创建的operationQueue中。创建过程都使用了以下的AFHTTPRequestOperationManager的类方法：

- (AFHTTPRequestOperation *)HTTPRequestOperationWithHTTPMethod:(NSString *)method
                                                     URLString:(NSString *)URLString
                                                    parameters:(id)parameters
                                                       success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                                                       failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
    NSError *serializationError = nil;
//直接通过manager的requestSerializer生成request
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
//如果在序列化过程中失败，则直接会在自定义的completionQueue或者mainQueue中调用failure block
    if (serializationError) {
        if (failure) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
#pragma clang diagnostic pop
        }
        return nil;
    }
    return [self HTTPRequestOperationWithRequest:request success:success failure:failure];
}

//创建opertaion，然后给这个request传入前面设置的responseSerializer
- (AFHTTPRequestOperation *)HTTPRequestOperationWithRequest:(NSURLRequest *)request
                                                    success:(void (^)(AFHTTPRequestOperation *operation, id responseObject))success
                                                    failure:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failure
{
//最终创建的AFHTTPRequestOperation
    AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
    operation.responseSerializer = self.responseSerializer;//给operation传入 response 解析器
//给operation传入其他的参数，主要是securityPolicy
    operation.shouldUseCredentialStorage = self.shouldUseCredentialStorage;
    operation.credential = self.credential;
    operation.securityPolicy = self.securityPolicy;

//给operation设置success&failure block，在operation执行完以后调用，
    [operation setCompletionBlockWithSuccess:success failure:failure];
//operation中引用对应的CompletionQueue和completionGroup，这个两个属性是在setCompletionBlockWithSuccess:failure:方法中设置的
    operation.completionQueue = self.completionQueue;
    operation.completionGroup = self.completionGroup;
    return operation;//返回生成好的的operation对象，直接在方法外部被加入到manager的queue中直接执行
}

3 AFHTTPRequestOperationManager调用方法总结

通过上面一般性的调用流程可以归纳如下：

• 首先通过[AFHTTPRequestOperationManager manager]方法对请求进行设置：主要包括请求序列化requestSerializer，responseSerializer，安全策略等等
• 创建 AFHTTPRequestOperation 对象 （*）
• 将operation对象加入到manager 的 operationQueue 中执行

在第二步创建operation对象又可以细分：

• 用manager.responseSerializer 创建 request 请求对象，称为请求序列化（*）
  • 如果请求序列化失败，在completionQueue中执行 failure block
• 直接alloc init 出 operation对象，设置responseSerializer属性，credential认证，securityPolicy安全策略等 （*）
• opertation设置completionBlock，operation setCompletionBlockWithSuccess:failure:（*）
• 设置operation 的 completionQueue, completionGroup 属性

还有一处值得学习：

- (NSError *)error {
//获取error的方法，因为在上层HTTP 层进行请求的 response 序列化,如果出错就返回这个错误，否则就返回URL 层的error
    if (_responseSerializationError) {
        return _responseSerializationError;
    } else {
        return [super error];
    }
}

requestSerilizer请求序列化 & responseSerilizer响应序列化会在后面讲解

参考：
http://blog.cnbang.net/tech/2320/
https://github.com/AFNetworking/AFNetworking/tree/2.x

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