AFNetworking - AFURLResponseSerialization源码解析

AFURLResponseSerialization 的作用是对请求返回的数据进行序列化

它有一个序列化的基类AFHTTPResponseSerializer，有六个不同的序列化的类继承于它

AFJSONResponseSerializer JSON格式数据响应
AFXMLParserResponseSerializer iOS端XML数据解析响应
AFXMLDocumentResponseSerializerMAC OS端XML数据解析响应
AFPropertyListResponseSerializerplist格式数据解析响应
AFImageResponseSerializer图片数据解析响应
AFCompoundResponseSerializer复合式数据解析响应

在序列化之前，有一个必要的工作，那就是校验响应是否有效，在基类AFHTTPResponseSerializer里面提供了一个核心方法，主要是是校验响应内容的类型和状态码

- (BOOL)validateResponse:(NSHTTPURLResponse *)response
                    data:(NSData *)data
                   error:(NSError * __autoreleasing *)error
{
    BOOL responseIsValid = YES;
    NSError *validationError = nil;

    if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {
        //如果返回的内容类型是不支持的类型，抛出错误
        if (self.acceptableContentTypes && ![self.acceptableContentTypes containsObject:[response MIMEType]] &&
            !([response MIMEType] == nil && [data length] == 0)) {

            if ([data length] > 0 && [response URL]) {
                NSMutableDictionary *mutableUserInfo = [@{
                                                          NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: unacceptable content-type: %@", @"AFNetworking", nil), [response MIMEType]],
                                                          NSURLErrorFailingURLErrorKey:[response URL],
                                                          AFNetworkingOperationFailingURLResponseErrorKey: response,
                                                        } mutableCopy];
                if (data) {
                    mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
                }

                validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorCannotDecodeContentData userInfo:mutableUserInfo], validationError);
            }

            responseIsValid = NO;
        }
        //如果返回的状态码不是200~299，抛出错误
        if (self.acceptableStatusCodes && ![self.acceptableStatusCodes containsIndex:(NSUInteger)response.statusCode] && [response URL]) {
            NSMutableDictionary *mutableUserInfo = [@{
                                               NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: %@ (%ld)", @"AFNetworking", nil), [NSHTTPURLResponse localizedStringForStatusCode:response.statusCode], (long)response.statusCode],
                                               NSURLErrorFailingURLErrorKey:[response URL],
                                               AFNetworkingOperationFailingURLResponseErrorKey: response,
                                       } mutableCopy];

            if (data) {
                mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
            }

            validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorBadServerResponse userInfo:mutableUserInfo], validationError);

            responseIsValid = NO;
        }
    }

    if (error && !responseIsValid) {
        *error = validationError;
    }

    return responseIsValid;
}

其他都是序列化操作，还有初始化方法，实现NSSecureCoding和NSCopying协议，这些都是大同小异，值得一提的是一个图片加载的分类，主要作用是对图片的解压，这里可以仔细看下bang's blog，里面做了比较详细解释