AjaxControlToolkit.AsyncFileUpload.OnPreRender C# (CSharp) Method

        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);

            string sendingControlID = this.Page.Request.QueryString[Constants.FileUploadIDKey];

            if(sendingControlID == null || sendingControlID == this.ClientID) {
                ReceivedFile(this.ClientID);
                if(sendingControlID != null && sendingControlID.StartsWith(this.ClientID)) {
                    string result;
                    if(_lastError == String.Empty) {
                        var bytes = this.FileBytes;
                        if(bytes != null)
                            result = bytes.Length.ToString() + "------" + ContentType;
                        else
                            result = String.Empty;
                    } else {
                        result = "error------" + _lastError;
                    }

                    TextWriter output = Page.Response.Output;
                    output.Write("<div id='" + ClientID + "'>");
                    output.Write(result);
                    output.Write("</div>");
                }
            }
        }