声明：这个类是对AFNetworking的二次封装

1.创建RequestManager类继承自NSObject

> 枚举
>//请求数据成功之后进行回调 返回NSData
typedef void(^Finish)(NSData *data);
> //请求数据失败之后进行回调 返回NSError
typedef void(^Error)(NSError *error);
>// 请求方式的枚举
typedef NS_ENUM(NSInteger, RequestType) {
    RequestGET,
    RequestPOST
};

声明属性

@property (nonatomic, copy)Finish finish;
@property (nonatomic, copy)Error error;
> 给外界的接口，写成类方法，可以让外界直接调用
+ (void)requestWithUrlString:(NSString *)urlString requestType:(RequestType)requestType parDic:(NSDictionary *)parDic finish:(Finish)finish error:(Error)error;

2.RequestManager.m

>类方法
+ (void)requestWithUrlString:(NSString *)urlString requestType:(RequestType)requestType parDic:(NSDictionary *)parDic finish:(Finish)finish error:(Error)error;
{
    RequestManager *request = [[RequestManager alloc] init];
    [request requestWithUrlString:urlString requestType:requestType parDic:parDic finish:finish error:error];
}
>方法的实现
- (void)requestWithUrlString:(NSString *)urlString requestType:(RequestType)requestType parDic:(NSDictionary *)parDic finish:(Finish)finish error:(Error)error;
{
    // 对block属性进行赋值
    self.finish = finish;
    self.error = error;   
    NSURL *url = [NSURL URLWithString:urlString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    request.timeoutInterval = 10;
    // 如果是POST请求
    if (requestType == RequestPOST)
    {
        [request setHTTPMethod:@"POST"];
        if (parDic.count > 0) {
            [request setHTTPBody:[self parDicToPOSTData:parDic]];
        }
    }
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (error) {
            self.error(error);
        }
        else  {
            dispatch_async(dispatch_get_main_queue(), ^{
                self.finish(data);
            });
        }
    }];
    //调用此方法 才是去异步链接
    [task resume];    
}
//拼接网址
- (NSData *)parDicToPOSTData:(NSDictionary *)parDic
{
    NSMutableArray *array = [NSMutableArray array];
    for (NSString *key in parDic)
    {
        NSString *string = [NSString stringWithFormat:@"%@=%@", key, parDic[key]];
        [array addObject:string];
    }
    NSString *postString = [array componentsJoinedByString:@"&"];
    return [postString dataUsingEncoding:NSUTF8StringEncoding];
}