Choosing a populated control using JavaScript results in an empty value

Within my ASP.NET applications, I incorporate a server-side HTML select control.

<select id="CompanyDropDown" runat="server" style="width:330px">
</select>

To populate and pre-select items in this control, I use a JavaScript function triggered by a link on the page. This implementation successfully displays all items with the correct one selected.

However, during a postback event such as clicking a button,

<asp:Button runat="server" ID="btnSaveCompany" Text="Save" 
    onclick="btnSaveCompany_Click" />

The CompanyDropDown.Value becomes empty and loses its list of items. Any recommendations for retaining the selected value after postback?

(Please note that attempting to utilize an ASP.NET DropDown control resulted in postback validation issues when adding items dynamically after rendering the page.)

javascriptasp.netselectpostback

Answer №1

When items are added to a list using JavaScript, they are not included in the viewstate and cannot be retrieved server-side. One way to address this is by using a server-side hidden field on your page and updating its value with JavaScript whenever the dropdown selection changes:

Here's a jQuery script example:

$('#CompanyDropDown').change(function() {
    $('#inpSelectValue').val($(this).val());
});

Include a hidden field in your markup:

<input runat="server" id="inpSelectValue" clientidmode="static" type="hidden" />

The value of the hidden field will be sent to the server during postback, allowing you to retrieve the selected item's value. Make sure to set clientidmode="static" for your dropdown as well to maintain consistent control IDs between server-side and client-side references (e.g., use CompanyDropDown instead of parentContainer_CompanyDropDown):

<select id="CompanyDropDown" runat="server" style="width:330px"
    clientidmode="static" />

Alternatively, if you need to track dynamically generated list items or changes in selection, consider using AJAX to communicate these updates to the server.

Answer №2

When working with JS, the manipulated values cannot be accessed on the server-side nor preserved during postback. A possible workaround is to store the SelectedValue in a hidden field. During page postback, you will need to reassign the SelectedValue from the hidden field.

Answer №3

To retrieve the selected option from CompanyDropDown, you can utilize Request.Form[CompanyDropDown.UniqueID] instead of using a hidden field for this purpose.

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