How do you display form validation error messages adjacent to the form fields in Blazor? How do you display a validation message specific to a field in a Blazor form?

You have to use the <ValidationMessage> tag with the “For” attribute lambda expression pointing to the form field.

[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 />

  <label for="firstname">First Name: </label>
  <InputText Id="firstname" @bind-Value="@person.FirstName"></InputText>
  <ValidationMessage For="@(() => person.FirstName)" />

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

  <label for="age">Age: </label>
  <InputNumber Id="age" @bind-Value="@person.Age"></InputNumber>
  <ValidationMessage For="@(() => person.Age)" />

  <button type="submit">Submit</button>
</EditForm>

@code {
    private Person person = new Person();
    private void HandleValidSubmit()
    {
        Console.WriteLine("OnValidSubmit");
    }
}