I try to use RadzenRequiredValidator but i get some trouble.
I have a dropdown and it doesn't work I
have an email RadzenTextBox, the warning message is shown but when i click on the submit button, the Radzen Card is closed.
Can you give somme support ?
Is it the radzen Card the trouble ?

RadzenCard isn't the trouble - our online demo uses it. Compare it with your code. Also check the documentation.

Last question : so, if requierd fields aren't filled, the dialog card page is not closes ?

I don't understand this. RequiredValidators do only two things:

  1. Prevent the Submit event of RadzenTemplateForm (InvalidSubmit is fired instead).
  2. Display the validation message specified via the Text attribute.

It's my trouble : the events doesn't fire.

I am afraid I can't help with so little information provided.

I think i made a mistake.
In fact, my Raszen card have data and in this case, i think i have to use an EditForm, isn't it ?

The documentation and demo that I linked before show how to use RadzenRequiredValidator.