// 将字典或者数组转化为JSON串+ (NSData *)toJSONData:(id)theData{    NSError *error = nil;    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:theData options:NSJSONWritingPrettyPrinted error:nil];        if ([jsonData length]&&error== nil){        return jsonData;    }else{        return nil;    }}// 将JSON串转化为字典或者数组+ (id)toArrayOrNSDictionary:(NSData *)jsonData{        NSError *error = nil;    id jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData                                                    options:NSJSONReadingAllowFragments                                                      error:nil];        if (jsonObject != nil && error == nil){        return jsonObject;    }else{        // 解析错误        return nil;    }    }