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Old January 6th, 2005, 01:46 PM
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Default postback issue with drop downlists with javascript

I have a problem with which I am struggling for many days.
I have a page which has six drop down list (which are webform elements and not html elements). Auto postback property is enabled for all the elements. The data in the dropdown lists are related in a hierarical fashion. Now to give you the general idea of the working of the page, suppose, When the client changes the selection in any of lists in the page (say list number 2), it updates the items of the subsequent lists (that is lists 3, 4, 5, 6). The process is database intensive, so it takes quite a while before any results comes up.
What I want is to prevent the client from changing the selection before their previous request is serviced, by disabling the dropdown lists in the page.
I am trying to use Javascript to disable the lists by adding a "OnChange" attribute to the dropdown list, in the Page_Load event of the page.
            ddllist1.Attributes.Add("OnChange", "disable();")
            ddllist2.Attributes.Add("OnChange", "disable();")
            ddllist6.Attributes.Add("OnChange", "disable();")
The disable function is defined on the <Head> of the aspx page. Now the trouble is, this "OnChange" event is suppressing the "OnSelectedIndexChanged" event of the dropdown lists!! So though the lists are getting disabled, when the client is changing the selection, the code in the "OnSelectedIndexChanged" is not executing and the lists are not getting updated.
Please suggest.

Old January 7th, 2005, 04:45 AM
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Do you mean prevent that after making a selection disable the current listboxes before the postback occurs or prevent them changing the fresh page before it has loaded. If the latter then add code to disable the listboxes until body.onload fires. If the former then post the source HTML of the listboxes, NOT the asp.net source.

These sort of problems have become quite common now that asp.net has abstracted the client side scripting by making all events submit back to the server. In the next version of asp.net you can aviod this and simply refresh the listboxes contents without a full postback.


Joe (Microsoft MVP - XML)
Old January 7th, 2005, 01:31 PM
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hello joefawcett,

Thanks for replying me back. It helped.


Old January 24th, 2005, 06:54 AM
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Will you please explain it in detail. I'm also facing the same problem

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