Class RadzenCustomValidator
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<TItem>. 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.
Inherited Members
Namespace: Radzen.Blazor
Assembly: Radzen.Blazor.dll
Syntax
public class RadzenCustomValidator : ValidatorBase, IComponent, IHandleEvent, IHandleAfterRender, IDisposable, IRadzenFormValidatorExamples
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
RadzenCustomValidator()
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<TItem>. 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.
Declaration
public RadzenCustomValidator()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" />Properties
Text
Gets or sets the error message displayed when the validation function returns false. Provide clear, actionable text explaining why the value is invalid and how to fix it.
Declaration
[Parameter]
public override string Text { get; set; }Property Value
| Type | Description |
|---|---|
| string | The validation error message. Default is "Value should match". |
Overrides
Validator
Gets or sets the validation function that determines whether the component value is valid. The function should return true if the value is valid, false if invalid. This function is called during form validation, so keep it fast or handle async operations appropriately.
Declaration
[Parameter]
public Func<bool> Validator { get; set; }Property Value
| Type | Description |
|---|---|
| Func<bool> | The validation function. Default returns true (always valid). |
Methods
Validate(IRadzenFormComponent)
Runs validation against the specified component.
Declaration
protected override bool Validate(IRadzenFormComponent component)Parameters
| Type | Name | Description |
|---|---|---|
| IRadzenFormComponent | component | The component to validate. |
Returns
| Type | Description |
|---|---|
| bool |
|