ios 解决AFN的post请求错误：Error Domain=

字典或者数组类型的参数应转成Json字符串的格式传给后台

[self dicToJsonStr:"rate_data" : [
                                                       {
                                                         "rate_id" : "43",
                                                         "good_id" : "6"
                                                       },
                                                       {
                                                         "rate_id" : "37",
                                                         "good_id" : "5"
                                                       },
                                                       {
                                                         "rate_id" : "33",
                                                         "good_id" : "4"
                                                       }
                                                     ],
]
- (NSString *)dicToJsonStr:(NSArray *)dic
{
    NSError *parseError = nil;
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:&parseError];
    return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
}