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when using javascript to assign text to an <asp:label> how do you then read that value in code behind vb.net

Posted on 2010-08-31
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Last Modified: 2012-05-10
I have spent hours figuring out how to set the text value of a label using javascript but now after that has been achieved I find that the VB code behind still sees the original default value even after it has been rendered on screen.

So is there anyway to send the output of a javascript back to the server? I thought I could do this using a server control but seems I can only change the rendering of that control, the server doesnt know the value changed.

What I am trying to do is retrieve the timezoneoffset value from the client and use that value to determine a selected item in a listbox.

Is this possible?

Any help is appreciated.
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Question by:JOHNFROG
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Expert Comment

by:silemone
ID: 33568219
are you using UpdatePanel?
If so, use PageRequestManager (which is javascript).  But with the Sys object, you have more interaction with your java and server controls...
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leakim971 earned 250 total points
ID: 33568243
You may sync the value with an hidden field
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Expert Comment

by:silemone
ID: 33568262
So since the client isn't refreshing, the server isn't seeing the new values...I would actually just surround the label with an Update Panel (if you only use these on that label, it will not slow down your website) and refresh on a server click, which will be asychronous and will cause only partial page refreshing...
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by:silemone
silemone earned 250 total points
ID: 33568270
The other way I was going to suggest would be a hidden field as leakim stated.
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Author Comment

by:JOHNFROG
ID: 33568279
yes I am using an update panel. I am starting to understand why thats causing a problem.

will look into PageRequestManager and using a hidden field. but will have to wait until tomorrow now. time has beaten me.
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Expert Comment

by:amit_g
ID: 33568293
asp:Label data is not posted back to server. Use hidden text field in addition to the label. On the client side set the value in the hidden field and then access it on the server.

<input runat="server" type="hidden" id="HiddenVar">
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Expert Comment

by:FredTang
ID: 33568434
please try this:

dim strLablevalue as string

strLablevalue=this.Lbl_id.value
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Author Closing Comment

by:JOHNFROG
ID: 33573295
Using the hiddenfield was the way to go. Although as I was using nested masterpages I had to extend the logic a bit.

To rtrieve the hiddenfield I used the following .vb  function
  Function getValueFromhiddenfield(ByVal curitem As String) As String
        Dim inpt As HtmlControls.HtmlInputHidden = TryCast(Me.Master.Master.FindControl(curitem), HtmlControls.HtmlInputHidden)
        Return inpt.Value
    End Function

And that did it for me.

Thanks for all your assistance
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Expert Comment

by:leakim971
ID: 33575865
You're welcome! Thanks for the points!
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