RadzenCustomValidator Class

A validator component that executes custom validation logic via a user-provided function. RadzenCustomValidator enables complex validation rules that cannot be achieved with built-in validators, such as database checks, cross-field validation, or business rule enforcement. Must be placed inside a RadzenTemplateForm<T>. Provides complete flexibility for validation logic by executing a Func<bool> that you define. The validator is valid when the function returns true, invalid when it returns false. Common use cases include uniqueness checks (validating email/username against existing database records), business rules (enforcing domain-specific validation logic), cross-field validation (validating relationships between multiple fields), API validation (checking values against external services), and any complex logic requiring custom code. The Validator function should return true for valid values and false for invalid values. The function is called during form validation, so keep it fast or use async patterns for slow operations.

Inheritance

Implements

Inherited Members

Syntax

public class RadzenCustomValidator : ValidatorBase, IComponent, IHandleEvent, IHandleAfterRender, IRadzenFormValidator

Examples

Uniqueness validation:

<RadzenTemplateForm TItem="Model" Data=@model>
    <RadzenTextBox Name="Email" @bind-Value=@model.Email />
    <RadzenCustomValidator Component="Email" Text="Email already exists" 
                           Validator=@(() => !existingEmails.Contains(model.Email)) 
                           Style="position: absolute" />
</RadzenTemplateForm>
@code {
    class Model { public string Email { get; set; } }
    Model model = new Model();
    string[] existingEmails = new[] { "user@example.com", "admin@example.com" };
}

Date range validation:

<RadzenDatePicker Name="StartDate" @bind-Value=@model.StartDate />
<RadzenDatePicker Name="EndDate" @bind-Value=@model.EndDate />
<RadzenCustomValidator Component="EndDate" Validator=@(() => model.EndDate > model.StartDate) 
                       Text="End date must be after start date" />

Constructors

public RadzenCustomValidator()

Properties

public string Text { get; set; }

public Func<bool> Validator { get; set; }

Methods

protected override bool Validate(IRadzenFormComponent component)