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Validation

note

The built-in ASP.NET validation can be used to validate the RadComboBox control.

To validate the content of RadComboBox, you just need to specify its ID in the ControlToValidate property of the validator. Validation is performed against the current Text property of the RadComboBox (the Text property of the currently selected item or the custom text entered in the RadComboBox' input field).

note

RadComboBox is validated by the Text property set to the items as these items not always have Values.

Validating the RadComboBox

Using ASP.NET Compare Validator

Compares the RadComboBox's text with the specified text in the CompareValidator's definition, using relations like less than, equal, not equal, etc.

.validationClass
{
    color: Red;
}   

<telerik:RadComboBox RenderMode="Lightweight" ID="RadComboBox1" runat="server">
    <Items>
        <telerik:RadComboBoxItem Text=" - Select a City - " Value="SelectCity" />
        <telerik:RadComboBoxItem Text="Paris" Value="Paris" />
        <telerik:RadComboBoxItem Text="Rome" Value="Rome" />
        <telerik:RadComboBoxItem Text="London" Value="London" />
    </Items>
</telerik:RadComboBox>
<asp:CompareValidator runat="server" ID="Comparevalidator1" ValueToCompare=" - Select a City - "
    Operator="NotEqual" ControlToValidate="RadComboBox1" ErrorMessage="You must select a city!"
    CssClass="validationClass" />

When the combobox text is "- Select a City -", the validator detects an error and displays the message "You must select a city!":

ComboBox Validator Fired

When the combobox text is set to a city, the validator accepts the selection:

ComboBox Validation Success

Using ASP.NET Required Field Validator

Validates to make sure the user entered a value.


<telerik:RadComboBox RenderMode="Lightweight" runat="server" ID="RadComboBox1">
    <Items>
        <telerik:RadComboBoxItem Text="" Value="EmptyItem" />
        <telerik:RadComboBoxItem Text="Paris" Value="Paris" />
        <telerik:RadComboBoxItem Text="Rome" Value="Rome" />
        <telerik:RadComboBoxItem Text="London" Value="London" />
    </Items>
</telerik:RadComboBox>
<asp:Button Text="Validate" runat="server" />
<asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator3" ControlToValidate="RadComboBox1"
    Display="Dynamic" ErrorMessage="You must select a city!" CssClass="validationClass"/>

Using ASP.NET Custom Validator

Validates the RadComboBox's text against custom validation logic that you, the developer, provide.



function validationFunction(source, args)
{
    if (args.Value == " - Select a City - ")
    {
        args.IsValid = false;
    } else
    {
        args.IsValid = true;
    }
}

<telerik:RadComboBox RenderMode="Lightweight" runat="server" ID="RadComboBox1" >
    <Items>
        <telerik:RadComboBoxItem Text=" - Select a City - " Value="SelectCity" />           
        <telerik:RadComboBoxItem Text="Paris" Value="Paris" />
        <telerik:RadComboBoxItem Text="Rome" Value="Rome" />
        <telerik:RadComboBoxItem Text="London" Value="London" />
    </Items>
</telerik:RadComboBox>
<asp:Button Text="Validate" runat="server" />
<asp:CustomValidator ErrorMessage='You must select a city!' ControlToValidate="RadComboBox1"
    ValidateEmptyText="true" runat="server" ClientValidationFunction="validationFunction"
    CssClass="validationClass" />

Causing Validation

The RadComboBox can trigger validation of other controls on the form when it performs a post-back to the server. To achieve this behavior, you need to set the CausesValidation property to True.

By default, all validators on the web page must be successful before a postback can occur. You can limit the controls that must be validated when the RadComboBox performs a post-back, while still allowing other controls on the web page to be validated, by using Validation Groups. The validator controls including RadComboBox, have a ValidationGroup property. The RadComboBox validation is activated only by those validators whose ValidationGroup property matches the ValidationGroup property of the RadComboBox.

When no ValidationGroup is specified, all validators will execute when a post-back to the server is made. The reason of this beahvior is that both the validators and the RadComboBox have an empty string set as a default value of the ValidationGroup property.


<div>
    <asp:Label runat="server" Text="Enter your name:" AssociatedControlID="textBox1" />
    <asp:TextBox runat="server" ID="textBox1"></asp:TextBox>
    <asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator1" ControlToValidate="textBox1"
        CssClass="customValidatorClass" Display="Dynamic" ErrorMessage="You must enter you name!"
        ValidationGroup="TextBoxValidationGroup" />
</div>
<div>
    <asp:Label runat="server" Text="Enter your destination:" AssociatedControlID="RadComboBox1" />
    <telerik:RadComboBox RenderMode="Lightweight" ID="RadComboBox1" runat="server" Skin="Default" CausesValidation="True"
        ValidationGroup="ComboBoxValidationGroup">
        <Items>
            <telerik:RadComboBoxItem Text="" Value="" />
            <telerik:RadComboBoxItem Text="Paris" Value="Paris" />
            <telerik:RadComboBoxItem Text="Rome" Value="Rome" />
            <telerik:RadComboBoxItem Text="London" Value="London" />
        </Items>
    </telerik:RadComboBox>
    <asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator2" ControlToValidate="RadComboBox1"
        CssClass="validationClass" Display="Dynamic" ErrorMessage="You must select a city!"
        ValidationGroup="ComboBoxValidationGroup" />
    <div>
        <!--When Search button is clicked, only validation controls that are a part of the 
specified ValidationGroup are validated.-->
        <asp:Button ID="Button1" runat="server" Text="Validate" ValidationGroup="TextBoxValidationGroup" />
    </div>
</div>

For a live example, see Validation Groups.