How to get EditContext.Validate() to work when binding EditForm to an array

First off, I'd suggest you do something like this

<EditForm EditContext="editContext" OnSubmit="Submit">

Instead of

<EditForm @ref="Form" Model="vms" OnSubmit="Submit">

Which requires you to define EditContext like this: EditContext editContext;

And instantiate the EditContext object in the OnInitialized method like this:

protected override void OnInitialized()
    {
        vms = new List<MyClass>() { new MyClass() { Code = "1111" },
                                    new MyClass() { Code = "2222" }
                                  };

        editContext = new EditContext(vms);
    }

Incidentally, why do you use OnSubmit instead of OnValidSubmit and OnInvalidSubmit ? Are you looking for challenges ?

EditContext.Validate() returns incorrect results

That is not true...

The issue is that you try to bind to an array of MyClass...But you should bind to a single object. Binding to an array is possible, but I can't extend on it as it merits a new question. Suffice it to say that the array of objects you can bind to must be itself a field (property) of an a single bounded object, as for instance, a Student object that contains a list of Languages he speaks.

In order to verify the above, change List<MyClass> vms;

into MyClass model = new MyClass();

and editContext = new EditContext(vms);

into editContext = new EditContext(model);

and instead of

 @foreach (var vm in vms)
  {
            <tr>
                <td>
                    <InputText @bind-Value="vm.Code"></InputText>
                    <ValidationMessage For="@(() => vm.Code)"> 
       </ValidationMessage>
                </td>
            </tr>
  }

code this:

<tr>
     <td>
        <InputText @bind-Value="model.Code"></InputText>
        <ValidationMessage For="@(() => model.Code)"></ValidationMessage>
     </td>
 </tr>

Now, run your code, and verify whether the defamation of the EditContext.Validate() was justified.

Update

The following code sample describes how to bind to a collection in an EditForm, and how to validate this collection as well as other fields in a model of which this collection is a field member.

Note: You should execute Install-Package Microsoft.AspNetCore.Components.DataAnnotations.Validation -Version 3.2.0-rc1.20223.4 in your Package ManagerConsole, to access objects necessary to make the sample work...

@page "/"
@using Microsoft.AspNetCore.Components.Forms
@using System.ComponentModel.DataAnnotations;

<EditForm EditContext="EditContext" OnSubmit="@OnSubmitHandler">
    @*<DataAnnotationsValidator />*@
    <ObjectGraphDataAnnotationsValidator/>
    <p>
        <label for="name">Enter name: </label>
        <InputText id="name" @bind-Value="customer.Name" /><br />
        <ValidationMessage For="@(() => customer.Name)" />
    </p>
    @foreach (var phone in customer.phones)
    {
<p>
    <label>Enter phone: </label>
    <InputText @bind-Value="phone.PhoneNumber" />
    <ValidationMessage For="@(() => phone.PhoneNumber)" />
</p>
    }

    <p>
        <button type="submit">submit</button>
    </p>

</EditForm>

<div>
    <p>Edit  customer</p>

    <p>@customer.Name</p>
    @foreach (var phone in customer.phones)
    {
        <p>@phone.PhoneNumber</p>

    }

</div>
<div>
     <p>Is model validated: @validated.ToString()</p>
 </div>
@code {
    EditContext EditContext;
    Customer customer;
    bool validated;

    protected override void OnInitialized()
    {
        customer = new Customer();
        EditContext = new EditContext(customer);

    }
    private void OnSubmitHandler()
    {            
        validated = EditContext.Validate();
    }

    public class Customer
    {
        [Required]
        public string Name { get; set; }  
        [ValidateComplexType]
        public List<Phone> phones { get; set; } = new List<Phone>() { new Phone { }, new Phone { }, new Phone { }};
         
    }

    public class Phone
    {
        [Required]
        public string PhoneNumber { get; set; }
    }

}