validating dropdown list in asp.net

Question

I have a web-form in which there are three drop downs as shown below in the image:

The form in the above image has 3 drop-down (Physical persons responsible for operations, Resident, Staff) and my task is that if nothing is selected it should display a warning message Please Select an Instrument Type

The .aspx code which I have used in order to achieve that is:

<asp:DropDownList ID="ddlInstrumentType2" runat="server" AutoPostBack="true">
</asp:DropDownList>
<asp:Label ID="InstrumentTypeSelected" runat="server" Visible="true"></asp:Label>
<asp:Image class="helpicon" ID="imgSelInst" runat="server" ImageUrl="~/images/help2.png" ToolTip="imgSelInst"/>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" InitialValue="---------   Select Instrument Type   ---------" ControlToValidate="ddlInstrumentType2"
   ErrorMessage="Please select an Instrument Type" ValidationGroup="vgrp1">*
</asp:RequiredFieldValidator>

The above code doesn't seems to validate as it doesn't display any warning message if I don't select anything from the dropdown. I am wondering what mistake I am doing and what changes I need to do in the above code so that it successfully displays warning if I don't select any dropdown.

Tetsuya Yamamoto · Accepted Answer · 2018-02-23 04:29:43Z

1

I expect your DropDownList doesn't have ListItem item value defined in InitialValue attribute, hence you need to use other value to trigger validation:

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" InitialValue="0" ControlToValidate="ddlInstrumentType2"
   ErrorMessage="Please select an Instrument Type" ...>*
</asp:RequiredFieldValidator>

Note: Make sure the validation group name defined in RequiredFieldValidator exists.

Or in your DropDownList (which supposed to be bound for data source) use a ListItem with initial value as first item:

<asp:DropDownList ID="ddlInstrumentType2" runat="server" AutoPostBack="true">
    <asp:ListItem Text="---------   Select Instrument Type   ---------" Value="---------   Select Instrument Type   ---------"></asp:ListItem> 
</asp:DropDownList>

Since RequiredFieldValidator control only works if ListItem is blank, the first approach should be enough.

answered Feb 23, 2018 at 4:29

Tetsuya Yamamoto

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1 Comment

john Over a year ago

I tried using 1st code

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" InitialValue="0" ControlToValidate="ddlInstrumentType2"    ErrorMessage="Please select an Instrument Type" ValidationGroup="vgrp1">* </asp:RequiredFieldValidator>

but it didn't work for some reasons.

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