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How do you validate forms in Blazor?

Platform: Blazor| Category: Forms and validation

The form validation in Blazor is achieved using data annotations. The following two tags are used for validations and display the validation error message:

  • <DataAnnotationsValidator />
  • <ValidationSummary />

Refer to the following code example for simple form validation in Blazor.

[Person.cs]

using System.ComponentModel.DataAnnotations;
public class Person
    {
        [Required]
        [StringLength(15, ErrorMessage = "{0} length must be between {2} and {1}.", MinimumLength = 6)]
        public string FirstName { get; set; }

        [Required]
        [DataType(DataType.Password)]
        [StringLength(15, ErrorMessage = "{0} length must be between {2} and {1}.", MinimumLength = 6)]
        public string LastName { get; set; }

        [Required]
        [Range(1, 100, ErrorMessage = "Age should a number between (1-100).")]
        public int Age { get; set; }
    }

[FormValidation.razor]

<EditForm Model="@person" OnValidSubmit="@HandleValidSubmit">
   <DataAnnotationsValidator />
   <ValidationSummary />
    <label for="firstname">First Name: </label>
    <InputText Id="firstname" @bind-Value="@person.FirstName"></InputText>

    <label for="lastname">Last Name: </label>
    <InputText Id="lastname" @bind-Value="@person.LastName"></InputText>

    <label for="age">Age: </label><br />
    <InputNumber Id="age" @bind-Value="@person.Age"></InputNumber>

    <button type="submit">Submit</button>
</EditForm>
@code {
    private Person person = new Person();
    private void HandleValidSubmit()
    {
        Console.WriteLine("OnValidSubmit");
    }
}

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