Blazor: How can I display validation messages when a form is displayed

Question

I'm using .NET 5 with Blazor Server Side

I want any validation error messages to be displayed when the form is first displayed (without having to submit the form or modify the fields). From what I read, it seemed that calling context.Validate() would do the trick but, alas, no.

Here's a paired-down page to illustrate the issue.

@page "/studentedit"
@using System.ComponentModel.DataAnnotations

<EditForm EditContext="@context">
    <DataAnnotationsValidator />

    <InputText @bind-Value="@student.FirstName"></InputText>
    <ValidationMessage For="@(() => student.FirstName)" />

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

@code {
    private Student student = new Student();
    private EditContext context;

    protected override async Task OnInitializedAsync()
    {
        context = new EditContext(student);
        context.Validate(); // <--- I thought this would work
        await base.OnInitializedAsync();
    }

    public class Student
    {
        [Required(ErrorMessage = "First Name is required")]
        public string FirstName { get; set; }
    }
}

Answer 1

On OnInitialized the ValidationMessage component is not instantiated yet and thus can not display any validation errors.

Calling EditContext.Validate in OnAfterRender works.

@page "/studentedit"
@using System.ComponentModel.DataAnnotations

<EditForm EditContext="@context">
    <DataAnnotationsValidator />

    <InputText @bind-Value="@student.FirstName"></InputText>
    <ValidationMessage For="@(() => student.FirstName)" />

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

@code {
    private Student student = new Student();
    private EditContext context;

    protected override void OnInitialized()
    {
        context = new EditContext(student);
        base.OnInitializedAsync();
    }

    protected override void OnAfterRender(bool firstRender)
    {
        if (firstRender)
            context.Validate();
    }

    public class Student
    {
        [Required(ErrorMessage = "First Name is required")]
        public string FirstName { get; set; }
    }
}