AFNetworking 关于JSON text did not start with array or object and option to allow fragments not set 错误

1、AFNetworking 报错Request failed: unacceptable content-type: text/html"
  解决：
 AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
 manager.responseSerializer = [AFHTTPResponseSerializer serializer];
 //注意不是json
manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"application/json"];
  manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/html"];

2、AFNetworking 报错：JSON text did not start with array or object and option to allow fragments not set 
解决：
在AFNetworking中 上述代码将会 输出

Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (JSON text did not start with array or object and option to allow fragments not set.) UserInfo=0x8ea19a0 {NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}
这是因为 AFNetworking默认把响应结果当成json来处理,(默认manager.responseSerializer = [AFJSONResponseSerializer serializer]) ,很显然,我们请求的百度首页 返回的并不是一个json文本,而是一个html网页,但是AFNetworking并不知道,它坚信请求的结果就是一个json文本!然后固执地以json的形式去解析,显然没办法把一个网页解析成一个字典或者数组,所以产生了上述错误.

然而,我们期望它能够正确地处理这个情形,而不是提示一个错误. 
这时候 你必须告诉AFNetworking:别把这个网页当json来处理! 
只需要在发送请求前加入:manager.responseSerializer = [AFHTTPResponseSerializer serializer]

代码变成:

    AFHTTPSessionManager *manager =[AFHTTPSessionManager manager];
    manager.responseSerializer = [AFHTTPResponseSerializer serializer];
    [manager GET:@"http://www.baidu.com" parameters:nil success:^(NSURLSessionDataTask *task, id responseObject) {
        NSString *result = [[NSString alloc]initWithData:responseObject encoding:NSUTF8StringEncoding];
        NSLog(@"%@",result);
    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"%@",error);
    }];