jQuery and ASP.NET controls visibility in code behind

Question

In my codebehind, I set the display property of an asp.net control to none as follows;

fuDoc.Attributes("style") = "display:none;" 'fuDoc is a FileUpload control.

On my page, if the user wants to upload a document, they click on a link, which by using jQuery, I set the display property to 'block' by using .show() as follows;

$('#fuDoc').show();

I also tried;

$('#fuDoc').attr('style', 'display:block;');

now, on form submit, I need to check if the fuDoc is visible and if so, do the standard file upload process e.g. check .HasFile etc..

However, although the fuDoc control is set to display:block in HTML with no problem, the following asp.net code always produces True

If fuDoc.Attributes("style") = "display:none;" Then 'always results to true

What is the reason for this? Any help would be appreciated.

Note: the FileUpload control is NOT created dynamically.

Codrin Eugeniu · Accepted Answer · 2012-03-26 09:29:08Z

2

The problem is that style attributes changes on the client are not persisted during a postback.

One possible fix would be use a hiddenfield to store the state of the fuDoc control.

answered Mar 26, 2012 at 9:29

Codrin Eugeniu

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1 Comment

Subliminal Hash Over a year ago

thank you codrin, voted up for being first, but had to accept the other since it includes example and might be helpful for others having similar problems.

Curtis · Accepted Answer · 2012-03-26 09:37:03Z

Rather than relying on detecting whether or not the FileUpload is visible on the page, you could include a TextBox or HiddenField such as:

<asp:TextBox id="txtIsFileUploadShown" runat="server" cssclass="txtisfileuploadshown" Text="0" style="display:none;" />

This control will be hidden on your page, storing the value of 0 by default.

Whenever you hide/show the file upload, change your code to also change this value:

$('#fuDoc').show();
$(".txtisfileuploadshown").val('1');

When hiding:

$('#fuDoc').hide();
$(".txtisfileuploadshown").val('0');

Then in your code-behind on post back, simply check:

If IsNumeric(txtisfileuploadshown.text) AndAlso Cint(txtisfileuploadshown.text)=1 Then
   'Do HasFile validation here.
End

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