Persisting variable after AsyncFileUpload call to OnUploadedComplete

问题

This is a strange one. So I have an Ajax Toolkit file uploader called AsyncFileUpload located in an update panel. This AsyncFileUpload control, as soon as you put a file there, begins to upload it and calls the server. I then store this file as a BLOB and obtain the row ID from a database table using SELECT @@IDENTITY. So far so good, I now have a row ID and I wish to store it. I placed it inside a hidden field but when AsyncFileUpload calls OnClientUploadComplete, hidden field is blank! So I thought "okay, I'll just store it in a ViewState". Much to my surprise, same thing happened; the viewstate gets cleared. Finally I had success with using a Session variable. My question is, why does Session variable work and ViewState or HiddenField do not?

FRONT:

<script type="text/javascript">
    function UploadComplete(sender, args) {
        var fileSize = args.get_length();
        if (fileSize > 2000000) {
            alert("Logo size must be smaller than 2MB");
        }

        $("[id*=hfUploadSuccessful]").val("1");
        //Calls a postback and thus lvMembers_PreRender gets executed to get results
        __doPostBack('<%=UpdatePanel1.ClientID %>', null);
    }
</script>

                                    <div id="divClassFileUpload">
                                        <asp:AsyncFileUpload ID="AsyncFileUpload1" runat="server" Width="350" CssClass="FileUploadClass floatLeft"
                                            UploaderStyle="Modern"
                                            CompleteBackColor="Lime"
                                            ErrorBackColor="Red"
                                            ThrobberID="Throbber"
                                            UploadingBackColor="#66CCFF"
                                            OnClientUploadError="uploadError" 
                                            OnClientUploadStarted="StartUpload"
                                            OnClientUploadComplete="UploadComplete"
                                            OnUploadedComplete="AsyncFileUpload1_UploadedComplete" />
                                    </div>

BACK:

    protected void AsyncFileUpload1_UploadedComplete(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e)
    {

            //hfSelectedArticleId.Value = dt.Rows[0]["ArticleId"].ToString());
            //ViewState.Add("ArticleId", dt.Rows[0]["ArticleId"].ToString());
            Session.Add("ArticleId", dt.Rows[0]["ArticleId"].ToString());

        }

EDIT: Found a similar post that sort of explains it. Thank you everyone! Not getting value in Viewstate in asp.net using C#?

来源：https://stackoverflow.com/questions/17580602/persisting-variable-after-asyncfileupload-call-to-onuploadedcomplete

标签

session

viewstate

asyncfileupload