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Editorial Team
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Asked: 2026-05-11T19:26:24+00:00

When I change ddl.Visible=true(it gets changed on partial postback/updatepanel from another form element event)the

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When I change ddl.Visible=true(it gets changed on partial postback/updatepanel from another form element event)the RequiredFieldValidator will not fire?

NOTE: This is not a question on how to use the RequiredFieldValidator in a normal circumstance. My form has cascading dropdowns that are all dynamically built with their visibility toggled on and off.

<asp:DropDownList ID="ddl" Visible="false" AutoPostBack="True" runat="server">                                                               
</asp:DropDownList>
<asp:RequiredFieldValidator ControlToValidate="ddl" 
ID="RequiredFieldValidator1" 
runat="server" ErrorMessage="Required"></asp:RequiredFieldValidator>
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1 Answer

  1. Editorial Team

    You need to set the InitialValue property on your RequiredFieldValidator so that it knows when the value of the DropDownList has changed. For example, on a dropdown with these values:

    • Please Select
    • Dog
    • Cat
    • Bird

    You would add this attribute 

    InitialValue="Please Select"

    to your RequiredFieldValidator.

    Without knowing if the value has changed it is impossible for the validator to know whether or not the user has satisfied its requirement.

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