【场景】文件上传时限制个数，仅适用于文件上传控件，针对其他附件文件服务器，附件数据库等既定的由平台实现的逻辑不能干预
【案例】上传多个文件时，服务端能够判断个数给客户提示（最终还是需要客户手动删除多余文件）
[文件上传逻辑](https://wenku.my7c.com/article/119433960857351680?productLineId=1&isKnowledge=2)
增加判断上传个数
```csharp
using Kingdee.BOS.Core.DynamicForm.PlugIn;
using Kingdee.BOS.Core.DynamicForm.PlugIn.Args;
using Kingdee.BOS.JSON;
using Kingdee.BOS.Util;
using System;
using System.Collections.Generic;
namespace DynamicFormPlugIn.Attachment
{
[Kingdee.BOS.Util.HotUpdate]
public class LimitFileCountPlugIn : AbstractDynamicFormPlugIn
{
const string FileUploadServicesDir = "FileUploadServices/UploadFiles";
const string FieldKey = "F_BHR_FileUpdate";
public override void CustomEvents(CustomEventsArgs e)
{
base.CustomEvents(e);
if (!string.Equals(FieldKey, e.Key, StringComparison.OrdinalIgnoreCase))
return;
// 设置上传控件参数
this.View.GetControl(FieldKey).SetCustomPropertyValue("NeedCallback", true);
this.View.GetControl(FieldKey).SetCustomPropertyValue("IsRequesting", false);
if (!string.Equals("FileChanged", e.EventName, StringComparison.OrdinalIgnoreCase))
return;
// 文件上传完毕
var postData = KDObjectConverter.DeserializeObject<JSONObject>(e.EventArgs);
if (postData == null)
return;
var uploadInfo = new JSONArray(postData["NewValue"].ToString());
if (uploadInfo.Count > 0)
{
if (uploadInfo.Count > 3)
{
//实际上文件已经上传到应用服务器对应目录，但是只是不做后续处理，如跟单据关联之类
this.View.ShowErrMessage("上传文件大于3个，不支持处理后续逻辑");
}
// 取上传的文件名
var fileInfo = uploadInfo[0] as Dictionary<string, object>;
if (fileInfo != null)
{
var fileName = fileInfo["ServerFileName"].ToString();
var physicalPath = PathUtils.GetPhysicalPath(FileUploadServicesDir, fileName);
this.View.ShowMessage("文件上传成功，存放路径：" + physicalPath);
}
}
}
}
}
```
【效果】如果上传多个，可以给操作员警告，后续的业务逻辑就不执行即可；满足条件时才做后续的逻辑
【缺陷】最终是在服务端判断，文件已上传到服务端，占用了上传的流量，前端无法干预实现此功能
