Telerik Validation Message for Blazor

The Telerik Validation Message for Blazor adds customization options on top of the standard .NET ValidationMessage, such as Template and Class parameters.

Using Validation Message with TelerikForm

To enable Telerik Validation Messages for a form field:

1. Add a <TelerikValidationMessage> tag near the respective <FormItem> tag, or inside a form item <Template>.
2. Provide a lambda expression in the For parameter that sets the associated property of the model, just like with the standard Blazor ValidationMessage component.
3. (optional) Disable the built-in validation messages of the Telerik Form to avoid repetition. Set ValidationMessageType="@FormValidationMessageType.None".

Use Telerik Validation Message in a TelerikForm

@using System.ComponentModel.DataAnnotations

<TelerikForm Model="@customer" Width="600px"
             ValidationMessageType="@FormValidationMessageType.None">
    <FormValidation>
        <DataAnnotationsValidator />
    </FormValidation>

    <FormItems>
        <FormItem Field="@nameof(Customer.CustomerName)" LabelText="Name" />
        <TelerikValidationMessage For="@(() => customer.CustomerName)" />

        <FormItem Field="@nameof(Customer.CustomerAge)" LabelText="Age" />
        <TelerikValidationMessage For="@(() => customer.CustomerAge)" />

        <FormItem Field="@nameof(Customer.EmailAddress)" LabelText="Email Address" />
        <TelerikValidationMessage For="@(() => customer.EmailAddress)" />
    </FormItems>
</TelerikForm>

@code {
    private Customer customer = new Customer();

    public class Customer
    {
        [Required(ErrorMessage = "Please enter your name")]
        [MaxLength(40, ErrorMessage = "The name must be up to 40 characters long")]
        public string CustomerName { get; set; }

        [Required(ErrorMessage = "Please enter your age")]
        [Range(18, 120, ErrorMessage = "You should be at least 18 years old to place an order")]
        public int CustomerAge { get; set; }

        [Required(ErrorMessage = "Please enter your email")]
        [EmailAddress(ErrorMessage = "Enter a valid email address")]
        public string EmailAddress { get; set; }
    }
}

Using Validation Message with EditForm

1. Replace the <ValidationMessage> tags with <TelerikValidationMessage> tags.
2. Provide a lambda expression in the For parameter that sets the associated property of the model, just like with the standard Blazor ValidationMessage component.

Use Telerik ValidationMessage in an EditForm

@using System.ComponentModel.DataAnnotations

<EditForm Model="@customer" width="600px">
    <DataAnnotationsValidator />

    <InputText @bind-Value="@customer.CustomerName"></InputText>
    <TelerikValidationMessage For="@(() => customer.CustomerName)" />
    <br />
    <InputNumber @bind-Value="@customer.CustomerAge"></InputNumber>
    <TelerikValidationMessage For="@(() => customer.CustomerAge)" />
    <br />
    <InputText @bind-Value="@customer.EmailAddress"></InputText>
    <TelerikValidationMessage For="@(() => customer.EmailAddress)" />
    <br />
    <input type="submit" value="Submit" />
</EditForm>

@code {
    private Customer customer = new Customer();

    public class Customer
    {
        [Required(ErrorMessage = "Please enter your name")]
        [MaxLength(40, ErrorMessage = "The name must be up to 40 characters long")]
        public string CustomerName { get; set; }

        [Required(ErrorMessage = "Please enter your age")]
        [Range(18, 120, ErrorMessage = "You should be at least 18 years old to place an order")]
        public int CustomerAge { get; set; }

        [Required(ErrorMessage = "Please enter your email")]
        [EmailAddress(ErrorMessage = "Enter a valid email address")]
        public string EmailAddress { get; set; }
    }
}

Template

The TelerikValidationMessage allows you to control its rendering via a nested <Template> tag. The context represents an IEnumerable<string> collection of all messages for this model property.

@using System.ComponentModel.DataAnnotations

<style>
    .custom-validation-message {
        color: blue;
        font-weight: bold;
    }
</style>

<TelerikForm Model="@customer" Width="600px"
             ValidationMessageType="@FormValidationMessageType.None">
    <FormValidation>
        <DataAnnotationsValidator />
    </FormValidation>

    <FormItems>
        <FormItem Field="@nameof(Customer.CustomerName)" LabelText="Name" />
        <TelerikValidationMessage For="@(() => customer.CustomerName)" />

        <FormItem Field="@nameof(Customer.CustomerAge)" LabelText="Age" />
        <TelerikValidationMessage For="@(() => customer.CustomerAge)">
            <Template>
                @{
                    IEnumerable<string> validationMessages = context;

                    @foreach (string message in validationMessages)
                    {
                        <div>
                            <TelerikFontIcon Icon="@FontIcon.XOutline"></TelerikIcon>
                            <span class="custom-validation-message">@message</span>
                        </div>
                    }
                }
            </Template>
        </TelerikValidationMessage>

        <FormItem Field="@nameof(Customer.EmailAddress)" LabelText="Email Address" />
        <TelerikValidationMessage For="@(() => customer.EmailAddress)" />
    </FormItems>
</TelerikForm>

@code {
    private Customer customer = new Customer();

    public class Customer
    {
        [Required(ErrorMessage = "Please enter your name")]
        [MaxLength(40, ErrorMessage = "The name must be up to 40 characters long")]
        public string CustomerName { get; set; }

        [Required(ErrorMessage = "Please enter your age")]
        [Range(18, 120, ErrorMessage = "You should be at least 18 years old to place an order")]
        public int CustomerAge { get; set; }

        [Required(ErrorMessage = "Please enter your email")]
        [EmailAddress(ErrorMessage = "Enter a valid email address")]
        public string EmailAddress { get; set; }
    }
}

Class

Use the Class parameter of the Validation Message to add a custom CSS class to the span.k-form-error. This element holds the validation message.

Using TelerikValidationMessage Class for EmailAddress.

@using System.ComponentModel.DataAnnotations

<style>
    .my-email-message {
        color: blue;
        font-weight: bold;
        text-decoration: underline;
    }
</style>

<TelerikForm Model="@customer" Width="600px"
             ValidationMessageType="@FormValidationMessageType.None">
    <FormValidation>
        <DataAnnotationsValidator />
    </FormValidation>

    <FormItems>
        <FormItem Field="@nameof(Customer.CustomerName)" LabelText="Name" />
        <TelerikValidationMessage For="@(() => customer.CustomerName)" />

        <FormItem Field="@nameof(Customer.CustomerAge)" LabelText="Age" />
        <TelerikValidationMessage For="@(() => customer.CustomerAge)" />

        <FormItem Field="@nameof(Customer.EmailAddress)" LabelText="Email Address" />
        <TelerikValidationMessage For="@(() => customer.EmailAddress)" Class="my-email-message" />
    </FormItems>
</TelerikForm>

@code {
    private Customer customer = new Customer();

    public class Customer
    {
        [Required(ErrorMessage = "Please enter your name")]
        [MaxLength(40, ErrorMessage = "The name must be up to 40 characters long")]
        public string CustomerName { get; set; }

        [Required(ErrorMessage = "Please enter your age")]
        [Range(18, 120, ErrorMessage = "You should be at least 18 years old to place an order")]
        public int CustomerAge { get; set; }

        [Required(ErrorMessage = "Please enter your email")]
        [EmailAddress(ErrorMessage = "Enter a valid email address")]
        public string EmailAddress { get; set; }
    }
}

Next Steps

• Explore TelerikValidationTooltip

See Also

• Live Demo: Validation
• TelerikValidationSummary
• TelerikValidationTooltip
• Form Component