论Web控件开发 - 完美上传下载控件

最近开发了一个文件上传下载控件，其支持的功能如下：

一、支持可设置不同权限级别的文件上传、下载、删除功能
二、支持验证器控件
三、支持扩展类型客户端和服务器端验证
四、支持FileSize属性

其界面如下：

测试站点为：http://www.keyss.cn:8888 （并不一直开放）

这个自定义控件主要由五个子控件组成一个htmlfileinput两个imagebutton(上传和删除)和一个Hyperlink（用来下载）另外一个为inputhidden用来保存文件名和支持客户端验证。

其主最要的代码如下：

        protected override void Render(HtmlTextWriter writer)
        {

            writer.AddAttribute(HtmlTextWriterAttribute.Cellpadding, "0");
            writer.AddAttribute(HtmlTextWriterAttribute.Cellspacing, "0");
            if(this.Width!=Unit.Empty)
                writer.AddAttribute(HtmlTextWriterAttribute.Width, Width.ToString());
            writer.AddAttribute(HtmlTextWriterAttribute.Border, "0");
            //table
            writer.RenderBeginTag(HtmlTextWriterTag.Table);
            writer.RenderBeginTag(HtmlTextWriterTag.Tr);
            //cell1
            writer.AddAttribute(HtmlTextWriterAttribute.Width, "98%");
            writer.RenderBeginTag(HtmlTextWriterTag.Td);
            this.FileUpload.Attributes.Add("id",this.ClientID+"__file");
            this.FileUpload.RenderControl(writer);
            writer.RenderEndTag();
            //cell2
            writer.AddAttribute(HtmlTextWriterAttribute.Nowrap,"Yes");
            writer.RenderBeginTag(HtmlTextWriterTag.Td);
            //hiden input file
            this.TxtFileName.Attributes.Add("id",this.ClientID);
            this.TxtFileName.RenderControl(writer);
            //upload btn
            WriteSpace(writer);
            string onClick = this.BtnUpLoad.Attributes["onclick"]==null?string.Empty:this.BtnUpLoad.Attributes["onclick"];
            this.BtnUpLoad.Attributes["onclick"] = string.Format("if(!({0}_obj.CheckUpload())) return false;",this.ClientID) + onClick;
            this.BtnUpLoad.RenderControl(writer);

            //delete btn
            if(this.AllowDelete) WriteSpace(writer); 
            onClick = (this.BtnDelete.Attributes["onclick"]==null)?string.Empty:this.BtnDelete.Attributes["onclick"];
            this.BtnDelete.Attributes["onclick"] = string.Format("if(!({0}_obj.CheckDelete())) return false;",this.ClientID)+ onClick;
            this.BtnDelete.RenderControl(writer);


            //download btn
            WriteSpace(writer);
            this.BtnDownload.Attributes["onclick"]=string.Format("if(!({0}_obj.CheckDownload(this))) return false;",this.ClientID);
            this.BtnDownload.RenderControl(writer);
            writer.RenderEndTag();
            
            writer.RenderEndTag();
            writer.RenderEndTag();
        }
        
        protected override void CreateChildControls()
        {
            this.Controls.Clear();
            //button hidden ctl0
            this._txtFileName = new System.Web.UI.HtmlControls.HtmlInputHidden();
            this.Controls.Add(this._txtFileName);

            //file upload ctl1
            this._fileUpload = new System.Web.UI.HtmlControls.HtmlInputFile();
            this._fileUpload.Style.Add("WIDTH","100%");
            if(this.CSS!=string.Empty)
                this._fileUpload.Attributes.Add("class",this.CSS);
            this.Controls.Add(this._fileUpload);

            //button upload
            this._btnUpLoad = new ImageButton();
            this._btnUpLoad.ImageUrl = this.UploadImg;
            if(this.UploadFileNameType != FileNameType.AutoGenerate)
                this._btnUpLoad.EnableWarning = true;
            else
                this._btnUpLoad.EnableWarning = false;
            this._btnUpLoad.AlternateText = this.UploadAlt;
            this._btnUpLoad.WarningMessage = "如果文件已经存在将被覆盖，确定吗？";
            this._btnUpLoad.CausesValidation = false;
            this._btnUpLoad.Click += new ImageClickEventHandler(Upload_Clicked);
            this.Controls.Add(this._btnUpLoad);

            //button delete
            this._btnDelete = new ImageButton();
            this._btnDelete.ImageUrl = this.DeleteImg;
            this._btnDelete.EnableWarning = true;
            this._btnDelete.AlternateText = this.DeleteAlt;
            this._btnDelete.WarningMessage = "确定要删除吗？";
            this._btnDelete.CausesValidation = false;
            this._btnDelete.Click +=new ImageClickEventHandler(Delete_Clicked);
            if(!this.AllowDelete)
                this._btnDelete.Visible = false;
            this.Controls.Add(this._btnDelete);

            //button download
            this._btnDownload = new HyperLink();
            this._btnDownload.Style.Add("cusor","hand");
            this._btnDownload.ImageUrl = this.DownloadImg;
            this._btnDownload.ToolTip = this.DownloadAlt;
            this._btnDownload.NavigateUrl = this.FullFileName;
            this._btnDownload.Target = "_blank";
            this._btnDownload.Text = "download";

            this.Controls.Add(this._btnDownload);

            ChildControlsCreated = true;
        }

重载了createchildcontrols 和render并且当上传或删除成功时触发afteroperation事件。在输出inputhidden时将clientID作为其id属性输出支持客户端验证。