后台要的格式
参数.png
我先保存为字典 然后转化成json
NSDictionary *dataDic = [NSDictionary dictionaryWithObject:picIdStr forKey:@"attach_ids"];
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dataDic options:NSJSONWritingPrettyPrinted error:&error];
NSString *extraStr = [[NSString alloc]initWithData:jsonData encoding:NSUTF8StringEncoding];
picIdStr是我之前存“1，2，3”的字符串
