RadMultiSelect doesn't seem to work with RequiredFieldValidator

[Rob]

I just get the following stacktrace:

An unknown error has occurred.Control '[ControlNamePlaceholder]' referenced by the ControlToValidate property of 'reqControlNamePlaceholder' cannot be validated

 

Is this by design, or is this control different than all the rest that do work with a requiredfieldvalidator?

[Rob]

Here is an example of the code in question
<asp:RequiredFieldValidator ID="reqControlNamePlaceholder" ControlToValidate="Test" EnableClientScript="true" ValidationGroup="Tests" ForeColor="Red" ErrorMessage="Required" runat="server"></asp:RequiredFieldValidator>


<telerik:RadMultiSelect runat="server" DataValueField="text" Placeholder="Select Test Value..." AutoClose="false" TagMode="Single" DataTextField="text" Width="100%" ID="ControlNamePlaceholder" ></telerik:RadMultiSelect>

[Rob]

Here is an example of the code in question
<asp:RequiredFieldValidator ID="reqControlNamePlaceholder" ControlToValidate="Test" EnableClientScript="true" ValidationGroup="Tests" ForeColor="Red" ErrorMessage="Required" runat="server"></asp:RequiredFieldValidator>

<telerik:RadMultiSelect runat="server" DataValueField="text" Placeholder="Select Test Value..." AutoClose="false" TagMode="Single" DataTextField="text" Width="100%" ID="ControlNamePlaceholder" ></telerik:RadMultiSelect>

[Peter Milchev]

Hello Rob,

I have logged the integration of the MultiSelect with the required field validator as a feature request in our Feedback portal where you can subscribe and get notified when there is any progress on it:

• https://feedback.telerik.com/aspnet-ajax/1468714-radmultiselect-integration-with-requiredfieldvalidator-and-controltovalidate-property

Meanwhile, you can use a custom validator as demonstrated below:

<telerik:RadMultiSelect ID="RadMultiSelect1" runat="server" DataTextField="text" DataValueField="value">
    <Items>
        <telerik:MultiSelectItem Text="Item 1" Value="1"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Item 2" Value="2"></telerik:MultiSelectItem>
        <telerik:MultiSelectItem Text="Item 3" Value="3"></telerik:MultiSelectItem>
    </Items>
</telerik:RadMultiSelect>

<telerik:RadButton runat="server" ID="RadButton1" Text="Postback" AutoPostBack="true" />

<asp:CustomValidator ErrorMessage="Please select an item" ClientValidationFunction="ClientValidationFunction" runat="server" />
<script>
    function ClientValidationFunction(sender, args) {
        var multiselect = $find("<%= RadMultiSelect1.ClientID %>");

        if (multiselect.get_value().length == 0) {
            args.IsValid = false;
        }
    }
</script>

As a small token of gratitude for bringing this to our attention, I have updated your Telerik points.

Regards,
Peter Milchev
Progress Telerik

[Rob]

Thanks Peter. I'll try this workaround. 

[Rob]

Yes, this workaround worked for me. Thanks!

[Hugo Augusto]

This solution is fine for just one control, but if you have multiple RadMultiSelect controls, you will need a more generic approach:

Here's my easy solution to be able to access the control to validate on client side.
Add the regular Custom Validator control with the options you might need.

   

<asp:CustomValidator ID="cvalShippingRegionCountries" ErrorMessage="Choose a country" ClientValidationFunction="ClientValMultiSelectCountries" runat="server" Display="Dynamic" SetFocusOnError="true" />

Then, in code behind, just add a custom attribute to store the clientID of the MultiSelect control to validate.

   

cvalShippingRegionCountries.Attributes.Add("ControlToValidateClientID", multiselectShippingRegionCountries.ClientID);

Now, in the function that deals with the validation you can access the value like this:

   

function ClientValMultiSelectCountries(sender, args) {

            var multiselect = $find(sender.attributes.controltovalidateclientid.nodeValue);

            if (multiselect.get_value().length == 0) {
                args.IsValid = false;
            }
        }

You will get the clientID inside your generic function ;)